Related Applications

This application claims the benefit of U.S. Provisional Application No.

62/461 ,346, filed February 21 , 2017, which is hereby incorporated herein by reference.

Field of Invention

The present invention relates to a cylinder, such as a pneumatic cylinder, for use in a contaminated environment such as in an agricultural field.

Background

Contamination in a pneumatic cylinder can cause premature wear on the cylinder and ultimately failure. In some applications the cylinder can be exposed to a very dirty environment in which dirt, debris and other contaminants can work their way into the cylinder and cause premature failure.

An example of such an environment is when pneumatic cylinders are used on tractor-pulled planters used for sowing seeds in an agricultural field. Planters include a row unit for distributing seeds in a trench. The trench is closed by a closer wheel, which is typically downwardly biased by a down force or pressure to ensure that the sides of the trench collapse over the seeds. The down force can be provided by an industrial air cylinder. Because the planter is towed behind a tractor, the cylinder is exposed to dirt, stones, fertilizer, debris and/or other contaminants present during the planting operation.

Existing pneumatic cylinders have various shortcomings, drawbacks, and disadvantages relative to agricultural and other dirty environment type applications. Conventional approaches to solving the problem of contamination in the cylinder relate to modifications intended to prevent contaminants from getting into the cylinder in the first place. For example, some solutions relate to the addition of more aggressive scrapers to keep dirt out of the cylinder, shielding from dust by using bellows around the piston rod, or using air bags in the place of an air cylinder. Single acting cylinders in other environments or applications may suffer from similar contamination effect.

A compounding problem with contaminants is that if the cylinder is double acting, then contaminants also can enter the cylinder through the second port. This problem can be addressed by running an air line from the second port to an area remote from the cylinder where contamination levels may be lower, such as from the tractor cab is not directly exposed to the contamination near the planter.

Accordingly, there remains a need for further contributions in this area of technology.

Summary of Invention

The cylinder disclosed herein includes a cylinder body having a cylinder chamber. The cylinder chamber is split into two compartments by a piston. The first compartment is sealed from the surrounding environment and is provided with pressurized gas to force the piston in one direction. The second compartment is open to the surrounding environment. In this manner, particulates in the

surrounding environment are allowed to freely pass into and out of the second compartment. Thus, rather than preventing contaminants from entering the cylinder, the cylinder disclosed herein is designed to allow contaminants to pass into and out of the cylinder, while preventing them from breaching the seal between the piston and the cylinder wall.

According to one aspect of the invention, a pneumatic cylinder includes a cylinder body having a chamber that includes an open end of the cylinder body; and, a piston slidably moveable within the chamber along an axis of the cylinder, the piston having a head portion that separates the chamber into a first

compartment and a second compartment, wherein the second compartment includes the open end of the cylinder body. The open end defines a passageway that couples the second compartment to a surrounding environment. Embodiments of the invention may include one or more of the following additional features separately or in combination.

The pneumatic cylinder may further include a guide element, and the piston may be slidably guided by the guide element.

The passageway may extend axially through the guide element from the second compartment side to an open end side of the guide element.

The passageway may extend substantially in the same direction as the movement axis of the piston.

The head portion of the piston may be at an axially opposite end of the second compartment from the guide element.

An annular portion of a second compartment side of the head portion may at least partially axially and radially align with an annular portion of a second compartment side of the guide element, and the annular portion of the second compartment side of the guide element may have the passageway extending axially therethrough.

The open end may define an annular shape lip, and the passageway may be defined by a space between the annular shape lip and a rod portion of the piston.

The passageway may extend axially through an opening in an end wall at the open end of the cylinder from a second compartment side to a surrounding environment side of the end wall.

The passageway may extend substantially in the same direction as the movement axis of the piston.

The head portion of the piston may be at an axially opposite end of the second compartment from the end wall.

An annular portion of a second compartment side of the head portion may at least partially axially and radially align with an annular portion of the second compartment side of the end wall, and the annular portion of the second

compartment side of the end wall may provide the passageway extending axially therethrough. According to another aspect of the invention, a pneumatic cylinder includes a cylinder body having a chamber that includes an open end of the cylinder body; a piston slidably moveable in the chamber, the piston having a head portion that separates the chamber into a first compartment and a second compartment, wherein the second compartment includes the open end of the cylinder body; and, a guide element at the open end of the cylinder body between the cylinder body and the piston, the guide element having a passageway that couples the second compartment to a surrounding environment.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The guide element may be annular and have a central hole through which the piston is moveable.

The guide element may have an inner perimeter surrounding the central hole that is at least partially in contact with the piston and an outer perimeter that is at least partially in contact with the cylinder body.

The guide element may include a closed inner diameter and a closed outer diameter.

The guide element may include a closed inner diameter and an open outer diameter.

The passageway may include a plurality of passages extending axially through the guide element and radially inward from the open outer diameter.

The passageway may include a plurality of radially spaced passages through the guide element.

The passages may be in a central portion of the guide element between an inner wall through which the piston is moveable and an outer wall that is at least partially in contact with the cylinder body.

The guide element may include an open inner diameter and a closed outer diameter.

The passageway may include a plurality of passages extending axially through the guide element and radially outward from the open inner diameter. A portion of the guide element surrounding the central hole may include a lead edge.

The lead edge may project toward the open end side of the cylinder and may be configured to scrape contaminants from the piston as the piston retracts back into the cylinder.

The lead edge may project toward the first compartment side of the cylinder and may be configured to scrape contaminants from the piston as the piston extends from the cylinder.

The guide element may be fixed relative to the cylinder housing and the piston may be slidably moveable relative to the guide element.

A scraper seal may be provided on a second compartment side of the head portion.

The guide element may be made of a porous material and the passageway may include pores or voids of the porous material.

The passageway may extend through a side wall of the cylinder body from a second compartment side to a surrounding environment side of the side wall.

According to another aspect of the invention, a pneumatic cylinder includes a cylinder body having a chamber that includes an open end of the cylinder body; a guide element; and, a piston slidably moveable in the chamber relative to and on the guide element, the piston having a head portion that separates the chamber into a first compartment and a second compartment, wherein the second compartment includes the open end of the cylinder body.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The guide element may include a rod that is coupled to the cylinder body, and the piston may include a bore, wherein the rod and the bore are in cooperative engagement with one another.

The rod may include a bore, and the port and the bore in the piston may be in fluid communication via the bore in the rod. The rod may include a crossbore that intersects the bore in the rod, and the first chamber may be in fluid communication with the port via the bore in the rod and the crossbore.

A scraper seal may be provided on a second compartment side of the piston head.

The following description and the annexed drawings set forth certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features according to aspects of the invention will become apparent from the following detailed

description when considered in conjunction with the drawings.

Brief Description of the Drawings

The annexed drawings, which are not necessarily to scale, show various aspects of the invention.

Fig. 1 is a cross-sectional view of an exemplary embodiment of a cylinder having a bearing;

Fig. 2A is a side view of an exemplary bearing;

Fig. 2B is a cross-sectional view of the bearing of Fig. 2A taken in the direction of 2B-2B in Fig. 2A;

Fig. 2C is a partial view based on the Fig. 2B view except that the Fig. 2C bearing is tapered and has a tapered bore.

Fig. 3A is a side view of an exemplary bearing;

Fig. 3B is a cross-sectional view of the bearing of Fig. 3A taken in the direction of 3B-3B in Fig. 3A;

Fig. 3C is an enlarged partial view of Fig. 3B, showing a relief and projection in greater detail;

Fig. 3D is a view based on the Fig. 3C view but showing the relief closed by the projection.

Fig. 4A is a side view of an exemplary bearing; Fig. 4B is a cross-sectional view of the bearing of Fig. 4A taken in the direction of 4B-4B in Fig. 4A;

Fig. 5A is a side view of an exemplary bearing;

Fig. 5B is a cross-sectional view of the bearing of Fig. 5A taken in the direction of 5B-5B in Fig. 5A;

Fig. 6 is cross-sectional view of an exemplary embodiment of a cylinder that does not have a bearing.

Detailed Description

While the present invention can take many different forms, for the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the described embodiments, and any further applications of the principles of the invention as described herein, are contemplated as would normally occur to one skilled in the art to which the invention relates.

Fig. 1 illustrates an exemplary embodiment of a cylinder 10 for use in a contaminated environment, such as on tractor-pulled planters used for sowing seeds in an agricultural field. The cylinder 10, which may be a pneumatic cylinder, includes a cylinder body 12 having a cylinder chamber 14 and a piston 20 slidably moveable axially in the cylinder chamber 14 along an axis A-A. The cylinder 10 may also include a guide element 22 for providing additional guiding movement of the piston 20. The cylinder chamber 14 includes an open end 28 of the cylinder body 12. The cylinder 10 also includes a port 34 for coupling the cylinder 10 to a supply of pressurized air to effect movement of the piston 20 at a closed end 36. The piston 20 has a head portion 38 that separates the cylinder chamber 14 into a compression compartment 40 (also referred to as a first compartment) and an extension compartment 42 (also referred to as a second compartment), where the extension compartment 42 includes the open end 28 of the cylinder body 12. As will be described in greater detail below, the open end 28 has a passageway 50 that couples the extension compartment 42 to a surrounding environment, identified generally by reference numeral 54 in Fig. 1 , such that the passageway 50

purposefully allows contaminants into and out of the cylinder 10. In the Fig. 1 embodiment, the guide element 22 is disposed at the open end 28 of the cylinder body 12 between the cylinder body 12 and the piston 20, and has the passageway 50 extending therethrough. In other embodiments, the guide element may be in the form of a rod along which the piston slides, or the guide element may be omitted.

It will be appreciated that the cylinders described herein and more

particularly the passageways thereof can be configured in any suitable way and need not be limited in any particular manner insofar as, for example, whether the passageway extends axially or radially or a combination of axially and radially, whether the passageway extends through a guide element or a guide element is omitted, the particular geometry of the passageways and the guide element, the quantity of structural pieces that make up the guide element and/or the

passageway, or how those pieces fit together, such as the manner by which the guide element is held in the cylinder body or otherwise how the guide element is mounted, what the guide element is made of, whether the guide element is separate from the passageway or whether the passageway is made of channels inside the guide element and/or formed by gaps or spaces in the guide element for example at the inner or outer perimeter of the guide element, the material that forms the passageway and/or guide element, among other considerations. Below are described several embodiments of the invention each having various features. The features of one embodiment may be combined with the features of another embodiment, as will occur to those skilled in the art upon the reading and

understanding of this specification and the annexed drawings.

Referring in greater detail to Fig. 1 , the piston 20 includes a central bore 56 which provides a surface for pressurized fluid to motivate the piston 20. The piston 20 has a rod portion 58, circular in axial cross section in the illustrated embodiment, which extends through the open end 28 of the cylinder 10. The head portion 38 also is circular in axial cross section in the illustrated embodiment and, as mentioned, separates the cylinder chamber 14 into the compression compartment 40 and extension compartment 42. The cylinder body 12 has a cylindrical tubular portion 60 extending from the closed end 36 (rightward in Fig. 1 ). The cylindrical tubular portion 60 has an interior surface 62 that is circular in axial cross section in the Fig. 1 embodiment. The head portion 38 corresponds in shape to the interior surface 62 to enable sliding of the head portion 38 within and relative to the interior surface 62.

The head portion 38 includes seals 70 and 72 disposed at its axially opposite ends. Seal 70 is disposed at an extension compartment side of the head portion 38, and seal 72 is disposed at a compression compartment side of the head portion 38. The seals 70, 72 may be PTFE seals that allow the cylinder 10 to run free from lubrication, which can attract and retain contaminants in the cylinder chamber 14. In one embodiment, the seals 70, 72 are spring-energized seals, which can provide sealing at lower pressures. Seal 70 may be a scraper seal that scrapes

contaminants from the interior surface 62 of the cylinder 10 as the piston 20 is extended. The scraped contaminants can then pass out of the cylinder 10 through the passageway 50 of the guide element 22. By removing any contaminants from the interior surface 62 of the cylinder 10 in this manner, any migration of

contaminants from the extension compartment 42 to the compression compartment 40 can be mitigated, which can extend the life of the cylinder 10 and/or prevent premature wear or failure. As will be appreciated, the seals 70, 72 can be made of materials other than PTFE, including other thermoplastics and even non- thermoplastics. Other suitable sealing materials may include, for example, nitrile, polyeurethane, or fluorocarbon. Also, the seals 70, 72 need not be made of materials that allow the cylinder 10 to run free from lubrication; seal materials requiring lubrication are also contemplated.

In the illustrated embodiment of Fig. 1 , the guide element 22 is a bearing that is located at or near the open end 28 of the cylinder body 12 and is disposed between the cylinder body 12 and the piston 20. The guide element 22 functions as a bearing to support and guide the piston 20 as well as a guide for guiding contaminants into and out of the cylinder 10. As afore described, the passageway 50 that extends through the bearing 22 fluidly couples the extension compartment 42 to the surrounding environment 54. In this way, the guide element 22, and thus the cylinder 10, is designed to withstand the rigors of a contaminated environment such as an agricultural field not by attempting to prevent entry of contaminants into the cylinder 10 but rather by purposefully allowing the contaminants to pass freely into or out of the extension compartment 42 via the passageway 50.

The guide element 22 can be made of any suitable material, the type of material depending on for example wear properties, operating temperatures, etc. Exemplary materials include any thermoplastic such as acetal, or metal material such as aluminum. The guide element 22 can be made by injection molding of a thermoplastic, or machining of metal material. Additive manufacturing may also be used, for example, for complex geometries. Other suitable materials for the guide element 22 may include, for example, sintered bronze, zinc aluminum, among others. It will further be appreciated that the guide element 22 can be made as a multi-piece guide element. For example, the guide element 22 could be made of a metal portion as an outer diameter piece and a bearing as an inner diameter piece, where the outer metal piece is fixedly attached to the inner diameter bearing piece, and the passageway 50 extends through the outer diameter metal piece.

An exemplary embodiment of the guide element 22, or bearing 22, is shown in Figs. 2A-2C. The guide element 22 can be an annular shape with a central hole 82. In one form, the guide element 22 can have an inner perimeter 84 that surrounds the central hole 82 and is at least partially in slidable contact with the piston 20, and an outer perimeter 86 that is at least partially in contact with the cylinder body 12, more specifically the interior surface 62 of the cylindrical tubular portion 60 thereof. In the Figs. 2A-2C embodiment, the central hole 82 is in the form of an axially extending bore 82 that is circular in shape in axial cross section, so that the guide element 22 has a continuous or closed inner diameter. The central bore 82, and more particularly the inner perimeter 84 that slidably contacts the piston 20, provides a support for the piston 20. The outer perimeter 86 of the Figs. 2A-2C guide element 22 also has a circular shape in axial cross section, so that the guide element 22 also has a continuous or closed outer diameter. It will be appreciated that the inner and outer perimeters 84, 86 of the guide element 22 need not take the form of continuous or closed diameters and may include gaps or spaces to further allow contaminants to pass into and out of the extension

compartment 42. As will be described further below, the outer perimeter 86 is fixed relative to the cylindrical tubular portion 60 of the cylinder body 12.

The inner perimeter 84 of the central hole 82 includes a lead edge 92 at the open end side or surrounding environment side of the guide element 22, as well as an edge 94 at the extension compartment side of the guide element 22. In the illustrated embodiment, the lead edge 92 is an annular surface that projects axially from surface 102 at the open end side or surrounding environment side of the guide element 22. The inner perimeter of the lead edge 92, like the remainder of the Figs. 2A-2C inner perimeter 84, has a circular shape in axial cross section. As such, the lead edge 92 has a continuous or closed inner diameter. As will be appreciated from Figs. 1 and 2B, the lead edge 92 slopes radially toward the piston 20 in a direction from the extension compartment side of the guide element 22 to the surrounding environment side or open end side of the guide element 22. The lead edge 92 thus forms an annular wedge 92 that, as shown in Fig. 1 , projects axially in a direction toward the open end side or surrounding environment side and has a radially inner surface that is slidable relative to the rod portion 58. The lead edge 92 can form a beveled edge, as illustrated in Fig. 2B, or form a curved edge. It will be appreciated that the lead edge 92, as with the inner perimeter 84 in general, need not take the form of a continuous or closed inner diameter, and may include gaps or spaces to further allow contaminants to pass into and out of the extension

compartment 42.

The edge 94 of the guide element 22 is likewise an annular surface but in the form of a curved surface that extends from surface 104 at the extension compartment side of the guide element 22 to the inner perimeter 84 of the guide element 22.

The piston 20 is slidably moveable relative to the guide element 22, or bearing 22, in the Figs. 2A-2C embodiment. By closely fitting the piston 20 within the bore 82, the lead edge 92 can function as a scraper to scrape and remove contaminants from the piston 20 as it retracts back into the cylinder 10. Similarly, edge 94 of surface 104 can scrape or remove contaminants from the rod portion 58 of the piston 20 when the piston 20 extends from the cylinder 10. Such

contaminants can be expelled from the cylinder 10 through the passageway 50.

Figs. 2A-2C show greater details of the passageway 50. The passageway

50 surrounds the central hole 82 and in the Figs. 2A-2C embodiment comprises a plurality of channels 124 separated by ribs 126. The channels 124 are radially spaced and extend axially through the guide element 22. As shown in Fig. 2A, the channels 124 are radially spaced between an inner wall 130 that defines the inner perimeter 84 and an outer wall 132 that defines the outer perimeter 86. As such, the channels 124 are in a central portion of the guide element 22, bound at radially opposite ends by the inner and outer walls 130, 132 and bound at circumferentially opposite sides by circumferentially adjacent ribs 126. The illustrated embodiment has 12 channels 124 and 12 ribs 126 distributed about the central axis of the guide element 22 circumferentially in alternating fashion and equally circumferentially spaced apart, although any quantity two or greater and any spacing, whether equi- circumferential or otherwise, may be suitable. As will be appreciated, the ribs 126 can provide support and rigidity to the bearing guide element 22. The guide element 22 can allow the cylinder 10 to handle side loads and can maintain alignment of the piston 20 relative to the cylinder body 12. As will further be appreciated, the plurality of ribs 126 provide a load path for radial loads between the piston 20 and cylinder body 12 via the inner perimeter 84 slidable contact with the piston 20 and the outer perimeter 86 contact with the cylinder body 12.

In the Figs. 2A-2C embodiment, the passageway 50 extends axially through the guide element 22 from an extension compartment side to an open end side or surrounding environment side of the guide element 22, wherein, as shown in Fig. 1 , the axis A-A defines the retract and extend slidable movement of the piston 20 within the cylinder chamber 14. As such, the passageway 50 that fluidly

communicates the contaminants into and out of the cylinder 10 extends

substantially in the same direction as the movement axis A-A of the piston 20. In addition, the head portion 38 of the piston 20 is at an axially opposite end of the extension compartment 42 from the guide element 22. As can be appreciated from Fig. 1 , an annular portion of the extension compartment side of the head portion 38 at least partially axially and radially aligns, or overlaps, with an annular portion of the extension compartment side of the guide element 22, which annular portion has the passageway 50 extending axially therethrough. These alignments aid in the passage of contaminants through the passageway 50. As the piston 20 retracts, contaminants flow into the extension compartment 42, which functions as a temporary holding compartment for the contaminants. As the piston 20 extends, the head portion 38 urges the contaminants from the extension compartment 42, aided by axial and radial alignment of the head portion 38 with the passageway 50, as well as by the scraper seal 70, if present, and/or the scraper edges 92, 94, if present.

The guide element 22 can be fixed relative to the cylindrical tubular portion 60 of the cylinder body 12, such as by crimping, staking, or folding the edge 140 of the cylindrical tubular portion 60 radially inward over the outer perimeter 86 of the guide element 22 at the open end side or surrounding environment side of the guide element 22 and compressing the edge 140 to hold the guide element 22 in place.

Other suitable ways to retain the guide element 22 relative to the cylinder body 12 may include welding, adhesive/glue, press fit, threading, retaining rings, among others. Those skilled in the art will appreciate that the manner of attachment may depend on the sizing constraints of a particular applicaton.

In Fig. 1 , the edge 140 is shown in an uncrimped, or pre-com pressed form for purposes of clarity. As shown in the inset of Fig. 1 , the interior surface 62 of the cylindrical tubular portion 60 may include a circumferential step 148 against which the outer perimeter 86 at the extension compartment side of the guide element 22 axially abuts, which, in conjunction with the crimped end, fixes the guide element 22 relative to the cylindrical tubular portion 60. The outer perimeter 86 may also be provided with a chamfer 150. The edge 140 can be configured such that, once compressed, the angle of the edge 140 matches the angle of the chamfer 150.

It will be appreciated that any suitable means may be used for securing the guide element 22 into the open end 28 of the cylinder 10. The securing need not be limited to the as shown construction of Fig. 1 , and other embodiments are

contemplated. For example, as shown in Fig. 2C, the cylindrical tubular portion 60 and outer perimeter 86 can be tapered in the direction from the open end side or surrounding environment side to the extension compartment side. The tapered portion 164 of the guide element 22 bottoms into the tapered portion 166 of the cylindrical tubular portion 60 to stop axial movement of the guide element 22 inwardly toward the extension compartment 42, which, in conjunction with the crimped end, fixes the guide element 22 relative to the cylindrical tubular portion 60.

Figs. 3A-3D, Figs. 4A-4C, and Figs. 5A-5B illustrate respective guide elements 322, 422, 522 according to other embodiments of the invention. The guide elements 322, 422, 522 in Figs. 3A-3D, Figs. 4A-4B, and Figs. 5A-5B are in many respects similar to the above-referenced Figs. 2A-2C guide element 22, and consequently the same reference numerals but indexed by 300, 400, 500

respectively, are used to denote structures corresponding to similar structures in the Figs. 2A-2C guide element. In addition, the foregoing description of the Figs. 2A-2C guide element is equally applicable to the guide elements 322, 422, 522 in Figs. 3A- 3D, Figs. 4A-4B, and Figs. 5A-5B except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the guide elements 22, 322, 422, 522 may be substituted for one another or used in conjunction with one another where applicable.

The guide element 322 has an annular star shape with a central hole 82. As with the Figs. 2A-2C embodiment, the Figs. 3A-3D guide element 322 has an inner perimeter 384 that surrounds the central hole 82 and is at least partially in slidable contact with the piston 20, and an outer perimeter 386 that is at least partially in contact with the cylinder body 12, more specifically the interior surface 62 of the cylindrical tubular portion 60 thereof. In the Figs. 3A-3D embodiment, the central hole 82 is in the form of an axially extending bore 82 that is circular in shape in axial cross section, so that the guide element 322 has a continuous or closed inner diameter. The central bore 82, and more particularly the inner perimeter 384 that slidably contacts the piston 20, provides a support for the piston 20. The guide element 322 has a passageway 350 that couples the extension compartment 42 to a surrounding environment such that the passageway 350 purposefully allows contaminants into and out of the cylinder 10.

The outer perimeter 386 of the Figs. 3A-3D guide element 322 has a star shape in axial cross section, and in this sense the guide element 322 has a noncontinuous or open outer diameter. The star shape guide element 322 has six axially extending radially protruding fingers 316 and six axially extending somewhat triangular shape gaps or spaces 318. The gaps 318 extend radially inward from the outer diameter, and form the noncontinuous or open portions in the outer diameter. The fingers 316 and triangular shape gaps 318 are distributed about the central axis of the guide element 322 circumferentially in alternating fashion and are equally circumferentially spaced apart, although any quantity two or greater and any spacing, whether equi-circumferential or otherwise, may be suitable. The triangular shape gaps 318 form part of the passageway 350 that extends axially from the extension compartment 42 to the surrounding environment 54 to allow contaminants to pass into and out of the extension compartment 42. As will be described further below, the fingers 316 of the outer perimeter 386 are fixed relative to the cylindrical tubular portion 60 of the cylinder body 12. It will be appreciated that the outer perimeter 386 need not take the form of a noncontinuous or open outer diameter, and may instead form a continuous or closed outer diameter. Further, it will be appreciated that the inner perimeter 384 may instead take the form of a

noncontinuous or open inner diameter and include gaps or spaces to allow contaminants to pass into and out of the extension compartment 42. The inner perimeter 384 of the central hole 82 includes first and second lead edges 392, 394 at opposite axial ends of the guide element 322, that is, at the respective open end side and extension compartment side of the guide element 322. The first lead edge 392 is substantially similar in construction and function as the lead edge 92 of the Figs. 2A-2C guide element 22. The second lead edge 394 is an annular surface that projects axially from surface 104 at the extension compartment side of the guide element 322. The inner perimeter of the second lead edge 394, like the remainder of the inner perimeter 384, has a circular shape in axial cross section. As such, the second lead edge 394 has a continuous or closed inner diameter. As can be appreciated from Figs. 1 and 3B, the second lead edge 394 slopes radially toward the piston 20 in a direction from the surrounding environment side or open end side of the guide element 322 to the extension compartment side of the guide element 322. The second lead edge 394 thus forms an annular wedge 394 that projects axially in a direction toward the extension compartment side and has a radially inner surface that is slidable relative to the rod portion 58. The second lead edge 394 can form a beveled edge, as illustrated in Fig. 3B, or form a curved edge. It will be appreciated that the second lead edge 394, as with the inner perimeter 384 in general, need not take the form of a continuous or closed inner diameter and may include gaps or spaces to further allow contaminants to pass into and out of the extension compartment 42.

The lead edges 392, 394 can perform a scraper function. The lead edge 392 can function as a scraper to scrape and remove contaminants from the piston 20 as it retracts back into the cylinder 10. The second lead edge 394 can function as a scraper to scrape and remove contaminants from the rod portion 58 of the piston 20 when the piston 20 extends from the cylinder 10. Such contaminants can be expelled from the cylinder 10 through the passageway 350.

The passageway 350 includes the plurality of triangular shape gaps 318, described above, as well as a plurality of channels 324. The plurality of channels 324 are separated by the triangular shape gaps 318 as well as by ribs 326 on opposite circumferential sides of the triangular shape gaps 318. The ribs 326 form part of the radially protruding fingers 316. The channels 324 are radially spaced and extend axially through the guide element 322. As shown in Fig. 3A, the channels 324 are radially spaced between an inner wall 330 that defines the inner perimeter 384 and respective outer wall arc portions 332 that define arc portions of the outer perimeter 386. As such, the channels 324 are in a central portion of the guide element 322, bound at radially opposite ends by the inner wall 330 and the outer wall arc portions 332 and bound at circumferentially opposite sides by circumferentially adjacent ribs 326 that form part of a radially protruding finger 316. The illustrated embodiment has six channels 324 and 12 ribs 326, each set of a channel 324 and pair of circumferentially adjacent ribs 326 being distributed about the central axis of the guide element 322 circumferentially in alternating fashion and equally circumferentially spaced apart, although any quantity two sets or greater and any spacing, whether equi-circumferential or otherwise, may be suitable. As will be appreciated, the ribs 326 can provide support and rigidity to the bearing guide element 322. The guide element 322 can allow the cylinder 10 to handle side loads and can maintain alignment of the piston 20 relative to the cylinder body 12. As will further be appreciated, the plurality of ribs 326 provide a load path for radial loads between the piston 20 and cylinder body 12 via the inner perimeter 384 slidable contact with the piston 20 and the outer perimeter 386 contact with the cylinder body 12.

Referring again to Fig. 3B, the outer perimeter 386 of the star shape guide element 322 includes six lead edge arc portions 396. The lead edge arc portions 396 project axially from the surface 104 at the extension compartment side of the guide element 322. The gaps between the lead edge arc portions 396 form the noncontinuous or open portions in the outer diameter of the star shape guide element 322. As shown in Fig. 3A, the lead edge arc portions 396 are at the radially outer ends of the respective six radially protruding fingers 316 of the guide element 322. As can be appreciated from Figs. 1 and 3B, the lead edge arc portions 396 slope radially toward the interior surface 62 of the cylinder 10 in a direction from the surrounding environment side or open end side of the guide element 322 to the extension compartment side of the guide element 322. The lead edge arc portions 396 thus form a plurality of circumferentially spaced wedge portions 396 that project axially in a direction toward the extension compartment side and have radially inner surfaces that are fixed relative to the interior surface 62 or otherwise in contact with the interior surface 62. The lead edge arc portions 396 can form beveled edges, as illustrated in Fig. 3B, or form curved edges. It will be appreciated that the lead edge arc portions 396, as with the outer perimeter 386 in general, need not form part of a noncontinuous or open outer diameter, and may instead form a continuous or closed outer diameter, for example, an annular shape single lead edge having a closed outer diameter.

The lead edge arc portions 396 can perform a guiding function. The lead edge arc portions 396 can guide contaminants urged along the interior surface 62 by the piston 20 radially inward toward the respective passageway channels 324. The contaminants can then be expelled through the respective passageway channels 324 as the piston 20 extends from the cylinder 10. The lead edge arc portions 396 can also guide contaminants radially inward toward the annular lead edge 394 to be deflected off the lead edge 394 and into the gaps 318 or channels 324 of the passageway 350.

In the Figs. 3A-3D embodiment, the passageway 350 extends axially through the guide element 322 from an extension compartment side to an open end side or surrounding environment side of the guide element 322, wherein, as shown in Fig. 1 , the axis A-A defines the retract and extend slidable movement of the piston 20 within the cylinder chamber 14. As such, the passageway 350 that fluidly

communicates the contaminants into and out of the cylinder 10 extends

substantially in the same direction as the movement axis A-A of the piston 20. In addition, the head portion 38 of the piston 20 is at an axially opposite end of the extension compartment 42 from the guide element 322. As can be appreciated from Fig. 1 , an annular portion of the extension compartment side of the head portion 38 at least partially axially and radially aligns, or overlaps, with an annular portion of the extension compartment side of the guide element 322, which annular portion has the passageway 350 extending axially therethrough. These alignments aid in the passage of contaminants through the passageway 350. As the piston 20 retracts, contaminants flow into the extension compartment 42, which functions as a temporary holding compartment for the contaminants. As the piston 20 extends, the head portion 38 urges the contaminants from the extension compartment 42, aided by axial and radial alignment of the head portion 38 with the passageway 350, as well as by the scraper seal 70, if present, and/or the scraper edges 392, 394, 396, if present.

The star shape guide element 322 is fixed relative to the cylindrical tubular portion 60 of the cylinder body 12 by folding or crimping the edge 140 of the cylindrical tubular portion 60 radially inward over the radially outer ends or outer wall arc portions 332 of the fingers 316 of the guide element 322. As shown in Fig. 3C, the cylindrical tubular portion 60 and the outer wall arc portions 332 of the fingers 316 can be tapered in the direction from the open end side or surrounding

environment side to the extension compartment side. The tapered portions 364 of the fingers 316 bottom into the tapered portion 366 of the cylindrical tubular portion 60 to stop axial movement of the guide element 322 inwardly toward the extension compartment 42, which, in conjunction with the crimped end, fixes the guide element 322 relative to the cylindrical tubular portion 60.

As shown in Figs. 3B and 3C, the outer wall arc portions 332 may also be provided with notches or reliefs 374 at the outer diameter of the guide element 322 at the surrounding environment side or open end side of the guide element 322. Each relief 374 spans the angular width of a respective outer wall arc portion 332 to form respective radially foldable spring-like projections 376. As shown in Fig. 3D, as the edge 140 of the cylindrical tubular portion 60 is crimped radially inward against the radially foldable projections 376, the projections 376 bend inward to close the respective reliefs 374 and form a smooth angled end surface 378. The folded edge 140 abuts the smooth angled end surface 378 to hold the guide element 322 in place. As will be appreciated, the reliefs 374 allow the edge 140 to be crimped to the guide element 322 without deforming or otherwise disrupting the inner geometry of the guide element 322. The projections 376 and reliefs 374 can be configured such that the projections 376 can fold inward and retain the guide element 322 without compressing or deforming the inner perimeter 384 where the rod portion 58 of the piston 20 slides. In this regard, the projections 376 function as springs that center, hold, and lock the guide element 322 in place. Of course, other suitable means may be used for securing the guide element 322 into the open end 28 of the cylinder 10, and other embodiments are contemplated; for example, the step and crimp of the Fig. 1 embodiment may be used to fix the star shape guide element 322 relative to the cylindrical tubular portion 60.

Figs. 4A and 4B illustrate a guide element 422 according to another embodiment of the invention. The guide element 422 has an annular shape with a central hole 482. As with the Figs. 2A-2C and Figs. 3A-3D embodiments, the Figs. 4A-4B guide element 422 has an inner perimeter 484 that surrounds the central hole 482 and is at least partially in slidable contact with the piston 20, and an outer perimeter 486 that is at least partially in contact with the cylinder body 12, more specifically the interior surface 62 of the cylindrical tubular portion 60 thereof. In the Figs. 4A-4B embodiment, the central hole 482 is in the form of an axially extending central bore portion 488 that is circular in shape in axial cross section, as well as a plurality, 10 in the illustrative embodiment, of axially extending radially protruding gaps 418 projecting radially outward from the central bore portion 488, so that the guide element 422 has a noncontinuous or open inner diameter. The central bore portion 488, and more particularly arc portions 432 of the inner perimeter 484 that slidably contact the piston 20, provide a support for the piston 20. The guide element 422 has a passageway 450 that couples the extension compartment 42 to a surrounding environment such that the passageway 450 purposefully allows contaminants into and out of the cylinder 10.

The guide element 422 has 10 axially extending radially protruding fingers 416 that project radially inwardly from an outer wall 464 of the guide element 422, as well as the 10 axially extending gaps 418 that are defined by the contour of the inner perimeter 484. The gaps 418 extend radially outward from the inner diameter, and the gaps 418 form the noncontinuous or open portions in the inner diameter. The fingers 416 and gaps 418 are distributed about the central axis of the guide element 422 circumferentially in alternating fashion and are equally circumferentially spaced apart. As will be appreciated, any quantity of fingers 416 and gaps 418, two or greater and any spacing, whether equi-circumferential or otherwise, may be suitable. The gaps 418 form the passageway 450 that extends axially from the extension compartment 42 to the surrounding environment 54 to allow contaminants to pass into and out of the extension compartment 42. It will be appreciated that the inner perimeter 484 need not take the form of a noncontinuous or open inner diameter, and may instead form a continuous or closed inner diameter. Further, it will be appreciated that the outer perimeter 486 may instead take the form of a noncontinuous or open outer diameter and include gaps or spaces to allow contaminants to pass into and out of the extension compartment 42.

The inner perimeter 484 of the central hole 482 includes first and second lead edge arc portions 492, 494 at opposite axial ends of the guide element 422, that is, at the respective open end side and extension compartment side of the guide element 422. The first lead edge arc portions 492 project axially from the surface 102 at the open end side or surrounding environment side of the guide element 422. The second lead edge arc portions 494 project axially from the surface 104 at the extension compartment side of the guide element 422. The gaps circumferentially between the lead edge arc portions 492, 494 form the

noncontinuous or open portions in the inner diameter portion of the lead edge arc portions. As shown in Fig. 4B, the lead edge arc portions 492, 494 are at the radially inner ends of the 10 radially protruding fingers 416 of the guide element 422. As can be appreciated from Figs. 1 and 4B, the first lead edge arc portion 492 slopes radially toward the piston 20 in a direction from the extension compartment side of the guide element 422 to the surrounding environment side or open end side of the guide element 422. The second lead edge arc portion 494 slopes radially toward the piston 20 in a direction from the surrounding environment side or open end side of the guide element 422 to the extension compartment side of the guide element 422. The lead edge arc portions 492, 494 thus form a plurality of circumferentially spaced wedge portions 492, 494 that project in axially opposite directions and have radially inner surfaces that are slidable relative to the rod portion 58. The lead edge arc portions 492, 494 can form beveled edges, as illustrated in Fig. 4B, or form curved edges. It will be appreciated that the lead edge arc portions 492, 494, as with the inner perimeter 484 in general, need not form part of a noncontinuous or open inner diameter, and may instead form a continuous or closed inner diameter, for example, in the form of annular shape single lead edges having closed inner diameters.

The first and second lead edge arc portions 492, 494 can perform a scraper function. The first lead edge arc portions 492 can function as scrapers to scrape and remove contaminants from the piston 20 as it retracts back into the cylinder 10. The second lead edge arc portions 494 can function as scrapers to scrape and remove contaminants from the rod portion 58 of the piston 20 when the piston 20 extends from the cylinder 10. Such contaminants can be expelled from the cylinder 10 through the passageway 450.

In the Figs. 4A-4B embodiment, the passageway 450 extends axially through the guide element 422 from an extension compartment side to an open end side or surrounding environment side of the guide element 422, wherein, as shown in Fig. 1 , the axis A-A defines the retract and extend slidable movement of the piston 20 within the cylinder chamber 14. As such, the passageway 450 that fluidly

communicates the contaminants into and out of the cylinder 10 extends

substantially in the same direction as the movement axis A-A of the piston 20. In addition, the head portion 38 of the piston 20 is at an axially opposite end of the extension compartment 42 from the guide element 422. As can be appreciated from Fig. 1 , an annular portion of the extension compartment side of the head portion 38 at least partially axially and radially aligns, or overlaps, with an annular portion of the extension compartment side of the guide element 422, which annular portion has the passageway 450 extending axially therethrough. These alignments aid in the passage of contaminants through the passageway 450. As the piston 20 retracts, contaminants flow into the extension compartment 42, which functions as a temporary holding compartment for the contaminants. As the piston 20 extends, the head portion 38 urges the contaminants from the extension compartment 42, aided by axial and radial alignment of the head portion 38 with the passageway 450, as well as by the scraper seal 70, if present, and/or the scraper edges 492, 494, if present.

The guide element 422 may be fixed relative to the cylindrical tubular portion 60 of the cylinder body 12 in a manner similar to that of the guide element 22, or any other suitable manner as described herein.

Figs. 5A and 5B illustrate a guide element 522 according to another embodiment of the invention. The guide element 522 is made of a porous material and has an annular shape with a central hole 582. As with the afore described embodiments of Figs. 2A-2C, Figs. 3A-3D, and Figs. 4A-4B, the Figs. 5A-5B guide element 522 has an inner perimeter 584 that surrounds the central hole 582 and is at least partially in slidable contact with the piston 50, and an outer perimeter 586 that is at least partially in contact with the cylinder body 12, more specifically the interior surface 62 of the cylindrical tubular portion 60 thereof. In the Figs. 5A-5B embodiment, the guide element 522 is similar in structure to the Figs. 2A-2D guide element 22 except that the passageway 550 is in the form of pores or voids of the porous material of which the guide element 522 is made, rather than a plurality of channels 124. As the inner and outer perimeters 584, 586 include pores, the guide element 522 can be said to have noncontinuous or open inner and outer diameters, wherein the pores themselves form the noncontinuous or open portions in the diameters.

The central hole 582 can be in the form of an axially extending central bore portion 588 that is circular in shape in axial cross section. The central bore portion 588 of the inner perimeter 584 slidably contacts the piston 20 to provide a support for the piston 20.

The passageway 550 formed by the pores or voids couples the extension compartment 42 to the surrounding environment 54 such that the passageway 550 purposefully allows contaminants into and out of the cylinder 10. The volumetric flow rate of contaminants through the passageway 550 will depend on the porosity of the porous material, including the size of the matrix or frame forming the porous material.

The guide element 522 can be made of any suitable porous material that would still enable the guide element to provide support for the piston 20 while coupling the extension compartment 42 in fluid communication with the open end 28, or surrounding environment 54, of the cylinder 10. For example, the guide element 522 could be made of sintered porous stainless steel, sintered porous bronze, sintered porous aluminum, porous aluminum, metal foam, and other metals, as well as non-metals such as polyethylene, polypropylene, polycarbonate, among others. In one form, the matrix/frame and porosity of the porous material is selected depending on the application and the particular debris expected to be encountered, to enable the debris to pass through the porous material.

It will be appreciated that the inner perimeter 584 need not take the form of a noncontinuous or open inner diameter, and may instead form a continuous or closed inner diameter; for example, an inner diameter made of a nonporous material. Similarly, the outer perimeter 586 may take the form of a continuous or closed outer diameter; for example, an outer diameter made of a nonporous material. In one form, the inner and outer diameters may be made of a nonporous material while the material radially therebetween may be made of a porous material.

The inner and outer perimeters 584, 586 may include first and second lead edges 592, 594 that function as scrapers in a manner substantially similar to the afore described scrapers 92, 94, or any other suitable scrapers as described herein.

In the Figs. 5A-5B embodiment, the passageway 550 extends axially through the guide element 522 from an extension compartment side to an open end side or surrounding environment side of the guide element 522, wherein, as shown in Fig. 1 , the axis A-A defines the retract and extend slidable movement of the piston 20 within the cylinder chamber 14. As such, the passageway 550 that fluidly

communicates the contaminants into and out of the cylinder 10 extends substantially in the same direction as the movement axis A-A of the piston 20. In addition, the head portion 38 of the piston 20 is at an axially opposite end of the extension compartment 42 from the guide element 522. As can be appreciated from Fig. 1 , an annular portion of the extension compartment side of the head portion 38 at least partially axially and radially aligns, or overlaps, with an annular portion of the extension compartment side of the guide element 522, which annular portion has the passageway 550 extending axially therethrough. These alignments aid in the passage of contaminants through the passageway 550. As the piston 20 retracts, contaminants flow into the extension compartment 42, which functions as a temporary holding compartment for the contaminants. As the piston 20 extends, the head portion 38 urges the contaminants from the extension compartment 42, aided by axial and radial alignment of the head portion 38 with the passageway 550, as well as by the scraper seal 70, if present, and/or the scraper edges 592, 594, if present.

The guide element 522 may be fixed relative to the cylindrical tubular portion

60 of the cylinder body 12 in a manner similar to that of the guide element 22, or any other suitable manner as described herein.

Fig. 6 illustrates a cylinder 600 according to another embodiment of the invention. The cylinder 600 in Fig. 6 is in many respects similar to the above- referenced Fig. 1 cylinder 10, and consequently the same reference numerals but indexed by 600, respectively, are used to denote structures corresponding to similar structures in the Fig. 1 cylinder 10. In addition, the foregoing description of the Fig. 1 cylinder 10 is equally applicable to the cylinder 600 in Fig. 6 except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the cylinders 10, 600 may be substituted for one another or used in conjunction with one another where applicable.

The cylinder 600 includes a cylinder body 602 having a cylinder chamber 604, a piston 610 and a guide element 622. The cylinder chamber 604 includes an open end 606 of the cylinder body 602. The piston 610 is slidably moveable in the cylinder chamber 604 relative to and on the guide element 622. The piston 610 includes a head portion 612 with a sealing arrangement 70, 72 that is substantially similar to that described with respect to the embodiment in Fig. 1 . The head portion 612 divides the cylinder chamber 604 into a compression chamber 614 (also referred to as a first chamber) and an extension chamber 616 (also referred to as a second chamber). The extension chamber 616 includes the open end 606 of the cylinder body 602. As will be described in greater detail below, the open end 606 of the cylinder body 602 couples the extension chamber 616 to a surrounding environment, identified generally by reference numeral 654 in Fig. 6, such that the open end 606 purposefully allows contaminants into and out of the cylinder 600.

Referring in greater detail to Fig. 6, the cylinder 600 includes a port 608 at a closed end 61 1 of the cylinder body 602 for coupling the cylinder 600 to a supply of pressurized air to effect movement of the piston 610. The compression chamber 614 is pressurized by air or fluid that enters the cylinder 600 through the port 608 to effect extension of the piston 610 from the cylinder body 602. When pressure is removed from the compression chamber 614, the piston 610 can retract back into the cylinder 600. The extension chamber 616 remains open to the environment due to the open end 606.

In the embodiment of Fig. 6, the guide element 622 is in the form of a rod 609 that is inserted into an internal bore 618 of the piston 610. The rod 609 is coupled to and fixed relative to the cylinder body 602 and the piston 610 slides back and forth on the rod 609. The guide element 622 can allow the cylinder 600 to handle side loads and can maintain alignment of the piston 610 relative to the cylinder body 602.

The rod 609 includes a bore 620 that is in fluid communication with the port 608 to supply pressurized fluid to the compression chamber 614 via a cross bore 623 that intersects the bore 620 in the rod 609. Pressurized fluid is also supplied to an internal chamber 624 in the piston 610 via the bore 620 in the rod 609.

Supplying pressurized fluid to the internal chamber 624 of the piston 610 and the compression chamber 614 of the cylinder 600 can provide efficiency advantages in the operation of the cylinder 600 by increasing the surface area on which the fluid pressure can act.

The Fig. 6 cylinder 600 is configured to purposefully allow contaminants to enter into and out of the extension chamber 616 via the open end side or surrounding environment side of the cylinder 600, in a manner substantially similar to the Fig. 1 cylinder 10 purposefully allowing contaminants to enter into and out of the extension compartment 42 via the open end side or surrounding environment side of the cylinder 10; that is, the open end 606, 28 allows fluid communication between the extension chamber or compartment 616, 42 and the surrounding environment.

In the Fig. 6 embodiment, the cylinder body 602 includes a cylindrical tubular portion 632 extending from the closed end 61 1 (rightward in Fig. 6) and the open end 606 is formed by an annular shape lip 630 that projects radially inwardly from the cylindrical tubular portion 632. An inner perimeter 634 of the lip 630, shown enlarged in the inset of Fig. 6, projects sufficiently inward to serve as a stop against axial movement of the head portion 612 of the piston 610 beyond the open end 606 of the cylinder 600. In the illustrative embodiment, the inner perimeter 634 is circular in shape in axial cross section, so that the annular shape lip 630 has a continuous or closed inner diameter. In a corresponding manner, the head portion 612 of the piston 610 has a boss 640 that abuts the extension chamber side of the lip 630 when the head portion 612 has reached a fully extended position within the cylinder chamber 604. An outer perimeter 644 of the boss 640 is circular in shape in axial cross section, so that the boss 640 has a continuous or closed outer diameter. As will be appreciated, the inner perimeter 634 of the lip 630 has at least some portions, a ring portion in the Fig. 6 embodiment, that axially overlap with the outer perimeter 644 of the boss 640 to prevent the head portion 612 from moving axially beyond the open end 606 of the cylinder 600. The angle L of the lip 630 relative to a plane perpendicular to the rotation axis A-A matches the angle B of the boss 640. It will be appreciated that any suitable retaining feature can be used that allows fluid communication between the extension chamber 616 and the

surrounding environment. The retaining feature need merely maintain an open end and stop the piston 610 from exiting the cylinder 600.

Further, it will be appreciated that the inner perimeter 634 of the lip 630 need not take the form of a continuous or closed diameter and may instead include gaps or spaces to further allow contaminants to pass into and out of the extension chamber 616. For example, rather than an annular shape lip 630, a plurality of circumferentially spaced tabs may be provided that project radially inwardly from the cylindrical tubular portion 632. Moreover, some portions of the inner perimeter 634, for example the radially inner portion of such tabs, may contact the rod portion 658 of the piston 610, and such portions may be configured as lead edge arc portions to perform a scraper function similar to the first and second lead edge arc portions 492, 494 of the guide element 422 of the Figs. 4A-4B embodiment. For example, in Fig. 6, first lead edge arc portions may project rightward from the lip 630 and slidably contact the rod portion 658 and function as scrapers to scrape and remove contaminants from the rod portion 658 as the piston 610 retracts back into the cylinder 600. Likewise, second lead edge arc portions can project leftward from the lip 630 and slidably contact the rod portion 658 and function as scrapers to scrape and remove contaminants from the rod portion 658 when the piston 610 extends from the cylinder 600. Such contaminants can be expelled from the cylinder 600 through the open end 606 for example through gap arc portions provided

circumferentially between the first and second lead edge arc portions.

The space between the annular shape lip 630 and the rod portion 658 in the Fig. 6 embodiment defines a passageway 650 substantially similar in function to the afore described passageways 50, 350, 450, 550. The passageway 650 extends axially through an opening 653 in an end wall 657 of the cylinder body 602 (thus the reference to 606 as an open end of the cylinder 600) from an extension

compartment side to a surrounding environment side of the end wall 657, wherein, as shown in Fig. 6, the axis A-A defines the retract and extend slidable movement of the piston 610 within the cylinder chamber 604. As such, the passageway 650 that fluidly communicates the contaminants into and out of the cylinder 610 extends substantially in the same direction as the movement axis A-A of the piston 610. In addition, the head portion 612 of the piston 610 is at an axially opposite end of the extension chamber 616 from the end wall 657. As can be appreciated from Fig. 6, an annular portion of the extension chamber side of the head portion 612 at least partially axially and radially aligns, or overlaps, with an annular portion of the extension chamber side of the end wall 657, which annular portion provides the passageway 650 extending axially therethrough. These alignments aid in the passage of contaminants through the passageway 650. As the piston 610 retracts, contaminants flow into the extension chamber 616, which functions as a temporary holding chamber for the contaminants. As the piston 610 extends, the head portion 612 urges the contaminants from the extension chamber 616, aided by axial and radial alignment of the head portion 612 with the end wall 657 and passageway 650 therein, as well as by the scraper seal 70, if present, and/or the scraper edges, if present.

In the above described embodiments, the cylinder 10, 600 is provided with a guide element. Also contemplated are cylinders for which there is no guide element. In applications where, for example, the piston is sufficiently long and/or the required stroke of the piston is sufficiently short and/or the side load is sufficiently low, a guide element such as guide element 22, 322, 422, 522 in Fig. 1 , or guide element 622 in Fig. 6, may be omitted. Thus, in the Fig. 2 embodiment, for example, the guide element 22 can be omitted and the head portion 38 of the piston 20 can, if desired, be lengthened. A stop can be formed at the edge 140 of the cylindrical tubular portion 60, for example, by folding the edge 140 radially inward or otherwise providing a stop as was described with respect to the Fig. 6 embodiment. Guiding of the piston 20 may be provided by the interface between the head portion 38 of the piston 20 and the cylindrical tubular portion 60 of the cylinder body 12. The open end 28 would still allow fluid communication between the extension compartment 42 and the surrounding environment 54, thus purposefully allowing debris and/or other contaminants to enter into and out of the extension compartment 42. In the Fig. 6 embodiment, for example, the guide element 622 can be omitted and the head portion 612 of the piston 610 can, if desired, be lengthened. Guiding of the piston 610 may be provided by the interface between the head portion 612 of the piston 610 and the cylindrical tubular portion 632 of the cylinder body 602. The open end 606 still allows fluid communication between the extension chamber 616 and the surrounding environment 654, thus purposefully allowing debris and/or other contaminants to enter into and out of the extension chamber 616.

In the above described embodiments, the cylinders 10, 600 provide for the passage of debris and/or other contaminants to enter into and out of the extension compartment or chamber 42, 616 by means of an open end passageway that extends axially through a guide element 22 (Fig. 1 ) or axially through an opening in an end wall (Fig. 6), such that the passageway couples the extension compartment or chamber 42, 616 to the surrounding environment 54, 654. Also contemplated are cylinders for which the passage of debris and/or contaminants enters into and out of the extension compartment or chamber by means of an open end passageway in a side wall of the cylinder body that couples the extension compartment or chamber to the surrounding environment. In the Figs. 1 and 6 embodiments, for example, the passageway can extend through a side wall of the cylinder body, for example the passageway can be in the form of one or more openings in the cylindrical tubular portion 60, 632 of the cylinder body 12, 602, that couple the extension compartment or chamber 42, 616 to the surrounding environment 54, 654. In one form, the side wall openings may extend radially through the side wall. The side wall opening passageway can be provided in addition to or as an alternative to the passageway extending axially through the guide element or the passageway extending axially through an opening in an end wall. In one form, the side wall openings may be machined into the cylindrical tubular portion 60, 632 of the cylinder body 12, 602. In one form, side wall openings may be provided to allow for the passage of debris and/or other contaminants, and a guide element without a passageway for debris and/or other contaminants may be provided for guiding the piston. In one form, side wall openings may be provided to allow for the passage of debris and/or contaminants, and an end wall without a passageway for debris and/or other contaminants may be provided with a bearing for guiding the piston.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and

understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.