The present invention relates, in general, to a drain valve particularly adapted for application to pneumatic systems, in particular air tanks, in particular for draining condensate, and the associated pneumatic circuit.

A system is known from patent application EP2774821 which automatically purges contaminants from a pressurized air tank when the emergency brakes of a vehicle are set. In a preferred embodiment, the system comprises a valve comprising an input port, an exhaust port, and a control port. The input port is in fluid connection with a drain on the pressurized air tank, and the control port is in fluid connection with an emergency brake line of the vehicle. When the emergency brakes are engaged, the valve is open so that the input port and the exhaust port are in fluid connection operable for air and contaminants from the pressurized air tank to be expelled from the pressurized air tank through the exhaust port. When the emergency brakes are not engaged, the valve is closed so that the input port and exhaust port are not in fluid connection.

Patent application FR1363011 discloses an automatic drain valve for removing oil and condensation products from a compressed-air system, The valve comprises a hollow body having an inlet valve and an outlet valve coupled together in a manner such that when one valve is open the other is closed, and vice versa, wherein biasing means are provided for biasing the valve. There is a coupling system such that in the idle position the inlet valve is open and the outlet valve is closed. There are actuator means for actuating the coupling system against the action of the biasing means in order to close the inlet valve and open the outlet valve, so that the hollow body can be emptied; the actuator means are pneumatic. The inlet and outlet valves comprise each a valve head co-operating with an annular seat; the two valve heads carry a single rod, so that the axial positioning of the rod allows reversing the position of the valves. The active surface of the outlet valve is larger than the surface of the inlet valve. The biasing means consist of a spring, and the actuator means comprise a diaphragm bearing set against the end of the valve rod, adapted to move the rod for reversing the position of the valves. There is an air intake under pressure exerted by one side of the diaphragm.

Application US6238013 discloses a contaminant-ejecting valve for a pneumatic brake system. Two embodiments of the valve are disclosed: in one embodiment, the valve is actuated by pilot air pressure, which is either supply air pressure or control air pressure; in another embodiment, the valve is solenoid-actuated. In both embodiments, the valve comprises a housing enclosing a chamber; a control port in the housing in fluid communication with the chamber; an exhaust port in the housing permitting removal of contaminants from the chamber; a main piston mounted within the chamber and movable between a first position and a second position; an exhaust passage through the main piston connecting the chamber and the exhaust port in fluid communication; and a blocking member movable between an open and closed position for opening and closing the exhaust passage, such that when the blocking member is in the open position it permits pressurized air from the control port to eject contaminants from the chamber. The main piston includes a hollow stem, and the blocking member comprises an exhaust piston slidably mounted within the hollow stem and movable between an exhaust passage open and an exhaust passage closed position.

Finally, application EP3173302 discloses a valve having an inlet, exhaust, control port, and diaphragm. The diaphragm moves between an open position, in which the inlet and exhaust are in fluid communication, and a closed position, in which the diaphragm blocks fluid from flowing between the inlet and the exhaust. The diaphragm moves from the closed position to the open position when an inlet force due to pressure at the inlet is greater than the sum of the biasing force and a control port force due to pressure at the control port. The valve is operable to automatically drain contaminants from a vehicle air reservoir when the vehicle's emergency brakes are set. To reduce noise, the diaphragm of the valve is preferably in tension when in the closed position, and/or the diaphragm opens a limited distance when in the open position so that a back pressure is generated at the inlet.

The present invention aims at improving the functionality of prior-art valves by providing an automatic drain valve capable of activating itself under a small difference in pressure between a tank and the valve chamber, thus avoiding the risk of contamination that might impair the valve's functionality.

One aspect of the present invention relates to a drain valve having the features set out in the appended claim 1,

Auxiliary features of the present invention are set out in dependent claims, which are an integral part of the present description.

The features and advantages of the present invention will become apparent in light of the different embodiments thereof described in the present patent application and illustrated in the annexed drawings, wherein:

• Figure 1 shows a valve in a sectional view relative to a vertical plane;

• Figure 2 shows an exploded view of the valve of Fig. 1;

• Figure 3 shows a sectional view of some details of the valve of Figure 1, wherein the first piston is in the closed position and the second piston is in the open position;

• Figure 4 shows a sectional view of some details of the valve of Figure 1, wherein the first piston is in the open position and the second piston is in the closed position.

With reference to the above-mentioned drawings, a drain valve 1 for pneumatic systems comprises: a valve body 2, defining a cavity, and comprising: a first inlet 4, whereupon compressed air contained in the tank is intended to act; a second inlet 5, whereupon the compressed air contained in the tank is intended to act; an outlet 6, adapted to be in communication with the outside of the tank; a chamber 3 intended to be filled with air coming from second inlet 5, and wherein such air is intended to exit chamber 3 through said outlet 6; an obstructor device comprising: a first piston 8 adapted to slide in said cavity and adapted to selectively close said outlet 6; wherein the first piston 8 is subject to the pressure of the air coming from the first inlet 4 and sealingly separates chamber 3 from said first inlet 4; a second piston 9 adapted to slide in said cavity and adapted to selectively put said second inlet 5 in fluidic communication with said chamber 3; wherein the second piston 9 is subject to the pressure of the air coming from the second inlet 5,

The first and second pistons 8, 9 are configured to take:

- a closed configuration, in which they prevent air from flowing to and from chamber 3;

- an intake configuration, in which air can flow into chamber 3 from the second inlet 5, and air cannot flow from chamber 3 through outlet 6;

- an ejection configuration, in which air cannot flow into chamber 3 from the second inlet 5, and air can flow from chamber 3 through outlet 6.

The first piston 8 is adapted to move as a function of the pressure acting upon it 8 through said first inlet 4, and as a function of the pressure in chamber 3,

The second piston 9 is adapted to move as a function of the pressure acting upon it 9 through said second inlet 5,

In particular, with reference to the drawings, the pressurized air in the tank acts upon a bottom face of an annular portion 52 of the second piston 9.

Therefore, the present invention advantageously permits purging valve 1 by just exploiting the pressure variations occurring in relation to the tank. Valve 1 is automatic and mechanical, and is therefore simple and economical.

The first inlet 4 is a portion of valve 1 that can put the pressurized air in the tank in fluidic communication with an outer part of the first piston 8. Conveniently, the second inlet 5 has a circumferential development.

Thus, chamber 3 has a variable volume. In particular, chamber 3 is delimited by valve body 2 and by pistons 8, 9. In particular, chamber 3 is located in the cavity of valve body 2.

The first piston 8 is adapted to sealingly separate said chamber 3 from the first inlet 4. Therefore, the pressurized air comes, through the first inlet 4, in contact with an outer portion of the first piston 8, In the example, the first piston 8 is elongate, in particular comprises a rod 12. In the example, the first piston 8 comprises also a head 14 that divides chamber 3 from the first inlet 4 (conveniently through an O-ring 16). The first piston 8 is adapted to slide along a straight trajectory, which is vertical in Fig. 1. Rod 12 is coaxial to said sliding axis. The second piston 9 is adapted to slide along a straight trajectory, which is vertical in Fig. 1. Pistons 8, 9 are slidable independently of each other.

In the closed configuration, pistons 8, 9 prevent air from flowing into chamber 3 from the second inlet 5, and from chamber 3 through outlet 6.

The first piston 8 is adapted to take a closed position (in Figs. 1 and 3, the lowered position), in which it 8 prevents air from exiting chamber 3 through outlet 6, and an open position (in Fig. 4, the raised position), in which such air outflow is allowed. In particular, there is a second return means 18, preferably an elastic means like a spring, which is adapted to bring the first piston 8 towards the open position. The second piston 9 is adapted to take a closed position (in Fig. 1, the lowered position), in which it 9 prevents air front flowing into chamber 3 from the second inlet 5, and an open position (in Fig. 1, the raised position), in which such inflow is allowed. In particular, there is a first return means 10, preferably an elastic means like a spring, which is adapted to bring the second piston 9 towards the closed position. In the example shown herein, return means 10, 18 are arranged around the first 8 and, respectively, the second piston 9, Conveniently, also the second piston 9 is fitted with respective O-rings 20, 21 for improved tightness. More in detail, O-ring 21 is located at an end of the second piston facing towards outlet 6.

Therefore, in the closed configuration pistons 8, 9 are in the closed position; in the intake configuration, the first piston 8 is in the open position and the second piston 9 is in the closed position; in the ejection configuration, the first piston 8 is in the closed position and the second piston 9 is in the open position.

In particular, valve body 2 comprises: a first portion 22, a second portion 24, and a central portion 26 interposed between the other two 22, 24. Such portions 22, 24, 26 are mutually assembled in a removable manner, conveniently by means of threads. For example, an O-ring 25 is mounted between portions 22, 26. In the example there is an additional O-ring 28, in particular mounted to the second portion 24, for sealing the valve body when it is mounted to the tank. In the example, the second portion 24 has an external thread 30 for mounting to the tank. Conveniently, valve 1 is mounted to the tank bottom, so that air and condensate will be directed towards valve 1, which is adapted to expel said air and condensate through outlet 6. Thus, inlets 4, 5 are located in the tank and are subject to pressurized air, whereas outlet 6 is in contact with the outside environment. The air in the tank is generally under higher pressure than the outside environment. For example, the tank or the pneumatic system comprises compressor means for generating pressurized air in the tank. The O-rings shown in the illustrated example may be replaced with other gaskets, which may be per se known.

With reference to the illustrated embodiment, most of the volume of chamber 3 is in the first portion 22, In the example, head 14 slides within the first portion 22, and the second piston 9 slides within central portion 26.

In particular, chamber 3 includes an accumulation chamber 31 that is comprised or arranged between pistons 8, 9. More in detail, accumulation chamber 31 is interposed between the second piston 9 and that part of the first piston 8 which is in contact with the first inlet 4, in this example head 14. Conveniently, accumulation chamber 31 includes most of the air volume that is present in chamber 3.

Preferably, the first and/or second pistons 8, 9 define a channel 32 to permit air to flow from the second inlet 5 to chamber 3 (in particular to accumulation chamber 31) when the second piston 9 allows air inflow (i.e. when it is in the open position), e.g. as shown in Fig. 3. Moreover, channel 32 permits air to flow from chamber 3 (in particular, from accumulation chamber 31) to outlet 6 when the first piston 8 allows air outflow (i.e. when it is in the open position), e.g. as shown in Fig. 4. In particular, channel 32 is formed in a radially internal position of the second piston 8, and in the illustrated example it crosses the latter axially.

Preferably, the second piston 9 has an axial cavity in which the first piston 8, in particular rod 12, is slidably housed. Channel 32 is defined between the outer surface of the first piston 8 (in particular, rod 12) and the inner surface of the second piston 9. In the example, channel 32 is disposed circumferentially around rod 12.

In the illustrated embodiment, the second piston 9 has a substantially cylindrical shape, in particular a circular cross-section. Also the cavity of valve body 2, particularly chamber 3, has a substantially circular cross-section. Valve 1 is substantially cylindrical also on the outside.

Conveniently, valve body 2 comprises, in particular on its outer surface, a filter 34 for filtering the air, located at the second inlet 5. In particular, filter 34 is annular and is disposed around the outer surface of valve body 2, in particular in a region across the second portion 24 and central portion 26. An additional filter 36 is located at outlet 6.

In accordance with the particular embodiment shown herein, an external cap 38 is mounted to valve body 2, in particular to the second portion 24, at outlet 6. In particular, a centering element 40 fits external cap 38 to one end of the first piston 8. Conveniently, there is an 0- ring 41 to ensure hydraulic sealing between external cap 38 and valve body 2, in particular the second portion 24. Optionally there is an additional gasket 42 between external cap 38 and valve body 2, in particular the second portion 24. In particular, Q-ring 21 is interposed between the second portion 24 and the second piston 9, and G-ring 20 is interposed between central portion 26 and the second piston 9.

Preferably, an end of the first piston 8 facing towards outlet 6 comprises a tapered tip 44, Such tip 44, which preferably has a circular cross-section, has a smaller diameter than a central part and/or an adjacent part of said first piston 8, in particular than rod 12. Thus, tip 44 and head 14 are two opposite ends of the first piston 8. Tip 44 is configured to fit into a seat 46 of valve body 2 in order to selectively close outlet 6. In particular, seat 46 is formed in external cap 38, in particular in centering element 40, which is located in a housing of external cap 38. In the example, seat 46 is a cylindrical cavity. In the illustrated example, tip 44 is connected to a wider portion by means of a shoulder 48 configured to abut on a supporting portion of valve body 2, of external cap 38 in the example, preferably resting on gasket 42, for closing outlet 6.

When the first piston 8 is in the open position, shoulder 48 is raised from the supporting portion of valve body 2; in the example, it 48 is spaced apart from gasket 42, thereby creating a passage that allows air to flow from chamber 3 towards outlet 6. In particular, from chamber 3 the air enters channel 32 and then reaches outlet 6.

When the second piston 9 is in the closed position, it prevents air from flowing from the second inlet 5 towards chamber 3 or towards outlet 6. In the illustrated example, when the second piston 9 is in the closed position, an abutment portion thereof 50, i.e. an end thereof in this example (the bottom end in Fig. 2), rests, conveniently through interposition of O-ring 21, on a supporting portion of valve body 2, in particular of the second portion 24. When the second piston 9 is in the open position, abutment portion 50 moves away from the supporting portion of valve body 2 and creates a passage for the air, which can thus flow towards the chamber, in particular through channel 32.

The following will describe how valve 1 operates. Starting from an initial condition, in which a substantially equal pressure (e.g. atmospheric pressure) is acting upon inlets 4, 5 and outlet 6, the second inlet 5 is closed under the effect of return means 10, whereas the outlet 6 is open, and therefore chamber 3 is in fluidic communication with the outside environment through the effect of return means 18, which pushes the first piston 8 towards the open position (upwards in Fig. 1); in this situation, the first piston 8 is in the open position and the second piston 9 is in the closed position. A pressure increase then occurs in the tank, which acts upon inlets 4, 5, and such pressure pushes the first piston 8 into the closed position (downwards in Fig. 1), and the second piston 9 remains in the closed position - this is the closed condition. The pressure in the tank increases until the pressure can move the second piston 9 into the open position (upwards in Fig. 1) by overcoming the resistance of return means 10; in this situation, pressurized air enters chamber 3, in which a pressure increase occurs - this is the intake condition. When pressurized air has entered the chamber, the second piston 9 returns into the closed position through the effect of return means 10. Subsequently, a pressure drop occurs in the tank, which may be followed by condensate formation. At this point, if the air pressure in the tank falls below a predetermined threshold, return means 18 will overcome such pressure acting upon head 14 and bring the first piston 8 back into the open position; at this time, the pressurized air in chamber 3 (in which the pressure is higher than in the outside environment) , is ejected through outlet 6 into the outside environment - this is the ejection condition. In this phase, any condensate that may have formed in the tank and entered chamber 3 will be drained as well.

It is thus possible to supply pressurized air into chamber 3 to effectively eject any condensate from the tank (and from valve 1 itself). Condensate may form for several reasons, which are per se known. Advantageously, no electric/electronic system is necessary to operate valve 1, which works exclusively by exploiting the air pressure variations occurring inside the tank.

Preferably, return means 10, 18 are adapted to exert different forces. In particular, the first return means 10 is adapted to exert a greater force than the second return means 18. For example, the spring associated with number 18 is staffer than the spring associated with number 10. This makes it possible to obtain that, when the pressure in the tank increases, the first piston 8 will move to close outlet 6, while the second piston 9 will remain in the closed position.

Optionally, valve 1 is at least partially made of plastic materials. Thanks to the low weight of plastic materials, low pressures are sufficient to move the components inside the valve, and the valve can thus be opened and closed by means of small pressure differences. For example, pistons 8, 9 are made of polymeric material. Valve body 2 may be made of metal. As an alternative, pistons 8, 9 may be made of metal. O-rings or gaskets are preferably made of polymeric material. The present invention makes it possible to economically realize a normally closed purge valve which is both reliable and durable.

The present invention further relates to a pneumatic tank or system comprising a valve 1 according to the invention, Conveniently, valve 1, the tank or the system belong to a vehicle, in particular for motor transport, such as an industrial vehicle, a truck, a bus, a trailer.

Any alternative embodiments which have not been described or illustrated in detail herein, but which could be easily inferred by a person skilled in the art in light of the present description and the annexed drawings, should be considered to fall within the protection scope of the present invention. /LT

REFERENCE NUMERALS

Valve 1

Valve body 2 Chamber 3 First inlet 4 Second inlet 5 Outlet 6

First piston 8

Second piston 9

First return means 10

Rod 12

Head 14

O-ring 16, 20, 21, 25, 28

Second return means 18 First portion 22 Second portion 24 Central portion 26 External thread 30 Accumulation chamber 31 Channel 32 Filter 34, 36

External cap 38

Centering element 40

Gasket 42

Tip

Seat

Shoulder 48

Abutment portion 50 Annular portion 52