The invention belongs to mechanical engineering, namely to piston oscillating machines and pumps as well as to components thereof.

The purpose of the invention is to create a piston pump for generating pressure in each hydraulic circuit, in which water could be used as hydraulic liquid, which could optionally and depending on each operating conditions be mixed with environment- friendly anti-freezing additives, and in which the pressure of min. 50 to at least approx. 250 bar should be available.

A state of the art pump is known to those skilled in the art, which is described in SI 22324 A and is used for driving and controlling of hydraulic cylinders. Such pump comprises a cylindrical operating chamber, in which the piston is inserted, which is able to oscillate to and fro in the axial direction and is pivotally interconnected with a crank, which is pivotally linked to an eccentric, which is driven by means of appropriate driving means and the central axis of which is aligned with the central axis of said cylinder. Said operating chamber is hydraulically interconnected on the one hand with a supplying conduit and on the other hand with a discharging i.e. compression conduit, wherein each conduit is furnished with a non-return valve, which is arranged adjacent to the operation chamber inlet or outlet respectively. When the piston is moving in its first direction, vacuum occurs within the operating chamber of the cylinder, and the hydraulic liquid starts flowing from the reservoir into the operation chamber. When the piston is moving in the opposite direction, compression occurs within the operation chamber, due which the nonreturn valve of the supplying conduit is closed and after that the non-return valve in the discharging conduit opens, so that compressed hydraulic liquid is discharged into said compression conduit and can be correspondingly transferred to each users which are included in the hydraulic circuit.

In practice, such pump is able to operate as a high pressure pump, by which said users are supplied with compressed hydraulic liquid, in which the pressure reaches 50 to at least 25 bar. Hydraulic oil is used as the liquid, the kinematic viscosity of which usually varies depending on temperature, although by correctly dimensioning of components such variations may still be acceptable, and each mutually contacting and cooperating surfaces of the cylinder and the piston are satisfactory lubricated even in the case, when the transversal forces, namely forces which act transversally to a direction of displacing the piston and result from oscillating of the eccentrically hinged and to the piston linked crank, are relatively high. Said temperature variations are not just a consequence of temperature variations in the surrounding air, but merely result from the heat which is generated during operation of the hydraulic circuit due to compression of the hydraulic media and due to resistance during circulation of the hydraulic media throughout the hydraulic circuit and different parts thereof, wherein due to properties of the oil as such in practice said heat is difficultly transferred away in a fluent and efficient manner.

Consequently, heating or even overheating of components in hydraulic circuits occur in the practice, which practically always results in certain risk of damages. Besides, numerous appliances with integrated hydraulic circuits are foreseen to operate in situ and in natural environment, in which every leakage, dropping or discharge of the hydraulic oil leads to undesired environment pollution. In order to avoid such problems, the use of environment-polluting hydraulic liquids and risks related thereto, should preferably be excluded.

The present invention refers to a high pressure piston pump, in particular for generating each desired pressure of a hydraulic liquid within each disposable high pressure hydraulic circuit in amounts between 50 and at least 250 bar, wherein such pump comprises a cylindrical operating chamber, in which a piston is inserted in a sealed manner and by maintaining a pre-determined gap towards the wall of said operating chamber and with the possibility of oscillating to and fro in the axial direction, for the purposes of which it is pivotally interconnected with a crank, which is pivotally attached to an eccentric, which is driven by appropriate driving means, wherein said operating chamber is hydraulically interconnected on the one hand with a supplying conduit and on the other hand with a discharging i.e. compression conduit, and wherein each of said conduits is furnished with a non- return valve located in the area of supplying the hydraulic liquid into said operating chamber or discharging thereof, and wherein the non-return valve of the supplying conduit is intended to allow the hydraulic liquid to flow from said supplying conduit towards the operating chamber but not also in the opposition direction, and wherein the non-return valve of the discharging conduit is intended to allow the hydraulic liquid to flow outwards from the operating chamber into the discharging conduit but not also in the opposite direction.

The invention provides that water is used as a hydraulic liquid, as well as that on the one hand at least an area of the internal wall of said cylindrical operating chamber, which is intended for cooperation with the external surface of the piston and is therefore at least temporarily brought into a direct contact therewith, consists of polyether-ether-ketone (PEEK), and on the other hand, at least an area of the external surface of the piston, which is intended for cooperation with said internal wall of the operating chamber and is during oscillations of the piston at least temporarily brought in contact with said internal wall of the operating chamber, consists of martensitic stainless steel, and at the same time, a driving eccentric of a crank, which is intended for providing oscillating movement of the piston to and fro along said operating chamber, is located at a pre-determined distance transversally offset with regard to the longitudinal central axis of said operation chamber, so that at least during the critical stage of movement of the piston i.e. during compression of the hydraulic liquid, the crank extends at least approximately along said longitudinal central axis of said operation chamber.

Said PEEK is preferably a PEEK containing 30% carbon fibers. In a preferred embodiment, the operating chamber is surrounded with a bush, which consists of PEEK and within which a piston is inserted, which consists of a martensitic stainless steel.

Said martensitic stainless steel is preferably a steel AISI 440B (DIN X 90CrMoV18). The piston consists of a martensitic stainless steel, which is preferably thermal treated, namely quenched and annealed, and optionally also furnished with a hard-chrome layer on its external surface.

Water as hydraulic liquid is optionally mixed with anti-freezing additive, which is selected from the group consisting of ethanol and ethylene glycol.

When the piston is moving in its first direction, vacuum is generated within the operation chamber of the cylinder, which leads to closing the non-return valve in the compression conduit and opening the non-return valve in the supplying conduit, so that each hydraulic liquid stars flowing from a reservoir into a cylinder. When subsequently the piston is moved in the opposite direction, compression occurs within the operating chamber, by which the non-return valve of the supplying conduit is closed, and the non-return valve of the discharging conduit is open, so that compressed hydraulic liquid flows through said discharging conduit towards each disposable users which are integrated in each hydraulic circuit.

The invention is described in connection with two piston pumps, which are shown in the attached drawing, wherein

Fig. 1 is a schematically presented high-pressure piston pump according to the state of the art, in which hydraulic oil is used as a hydraulic liquid; and

Fig. 2 is also a schematically presented high-pressure piston pump according to the invention, in which pure water is used as a hydraulic liquid. A piston pump according to Figs. 1 and 2 comprises a cylindrical operating chamber 1, in which a piston 2 is inserted with the possibility of oscillating to and fro in the axial direction by simultaneously forming a pre-determined and sealed gap between it and the internal wall 10 of said operating chamber 1, wherein said piston 2 is pivotally interconnected with a crank 21, which is pivotally linked to an eccentric 22, which is driven by means of appropriate driving means 3.

Said operating chamber 1 is on the one hand hydraulically interconnected with the supplying conduit 4 and on the other hand with the discharging i.e. compression conduit 5. Each of said conduits 4, 5 is furnished with a non-return valve 41, 51 which is arranged in the area of supplying the hydraulic liquid into said operating chamber 1 and in the area of discharging thereof, respectively, wherein the nonreturn valve 41 of the supplying conduit 4 enables the liquid to flow from said supplying conduit 4, e.g. from a reservoir 40 towards said operating chamber 1 but not also in the opposite direction, and wherein the non-return valve 51 of the discharging i.e. compression conduit 5 allows the liquid to flow from the operating chamber 1 into said compression conduit 5 and towards each user of the compressed hydraulic liquid, but not also in the opposite direction.

Regarding the known pump according to Fig. 1, it is adapted to use oil as a hydraulic liquid, in particular a special hydraulic oil, which is normally used in various hydraulic circuits, and said eccentric 22 is arranged in such a manner that its rotation axis 220 is located essentially on the central axis 100 of said operating chamber 1.

Regarding the invented pump according to Fig. 2, the invention provides that environment-friendly water is used as a hydraulic liquid. Contrary to the oil, water is not a lubricant and also cannot protect metallic components against corrosion. Regardless to that, by taking into consideration all prescribed measures, which are defined below, water appears to be a perfect high-pressure hydraulic liquid having a lower compressibility than oil, and kinematic viscosity, which is even less dependent on temperature variations than by oil. Moreover, by taking into consideration basic operational instructions, several further features and phenomena of the water like pH, hardness, content of microorganisms and content of air can be easily controlled in practice in such a way that reliable operating of valves and the complete hydraulic systems within the frame of each regular use.

To this aim, on the one hand at least an area of the internal wall 10 of said cylindrical operating chamber 1, which is intended for cooperation with the external surface 20 of the piston 2 and is therefore at least temporarily brought in contact therewith, consists of polyether-ether-ketone (PEEK), and on the other hand, at least an area of the external surface 20 of the piston 2, which is intended for cooperation with said internal wall 10 of the operating chamber 1 and is during oscillations of the piston 2 at least temporarily brought in contact with said internal wall 10 of the operating chamber 1 , consists of martens itic stainless steel, which is optionally subjected to thermal treatment by quenching and annealing, and is moreover by optionally plated with chrome, namely galvanized with hard-chrome.

Simultaneously, a driving eccentric 22 of a crank 21, which is intended for providing oscillating movement of the piston 2 to and fro along said operating chamber 1, is located at a pre-determined distance e offset with regard to the longitudinal central axis 100 of said operation chamber 1 , so that at least during the critical stage of movement of the piston 2 i.e. during compression of the hydraulic liquid, the crank 21 extends at least approximately along said longitudinal central axis 100 of said operation chamber 1. Thanks to said approach, during such critical phase, where maximum stresses occur due to compressing the hydraulic liquid during displacement of the piston 2 from the right toward the left in accordance with Fig. 2, each transversal forces which are acting to the piston 2 and also the contacting compression between the external surface 20 of the piston 2 and the internal wall 10 of the operating chamber 1 are then essentially reduced.

Such combination of measures, namely said choice of materials of the external surface 20 of the piston 2 and the internal surface 10 of the operating chamber 1 in combination with the above described position of the crank 21 during the stage of critical stresses due to compression of the hydraulic liquid, long-term oscillating of the piston 2 within the operating chamber 1 is feasible without any problems.

In a preferred embodiment of the invention, the operating chamber 1 is surrounded with a bush 10' consisting of PEEK, within which the piston 2 is inserted, which consists of martensitic stainless steel, which is optionally thermal treated by quenching and annealing, and optionally also hard-chrome plated.

The term PEEK is abbreviation of a commonly used English expression "polyether-ether-ketone", which is used to define a plastics, namely a technical plastics i.e. semi-crystallinic thermoplastics having a melting temperature at approx. T=340°C and a glass temperature at approx. T=140 ^° C, and is moreover characterized by low water absorption rate, which is usually approx. 0,1%. The PEEK CA30, which is produced by QUADRANT, includes approx. 30% carbon fibers and is commercially available under trademark Ketron ^® . Due to said carbon fibers, the material becomes more rigid and resilient and herewith also more resistant against wearing and plastic extensions. Due to the presence of said carbon fibers, a thermal conductivity is 3,5-times higher than by pure PEEK, which means that the intensity of heat transfer from the contact surface is 3,5-times higher than in pure PEEK. Consequently, the PEEK with 30% carbon fibers should be preferably used in a pump according to the invention.

The piston 2 of the pump according to the invention preferably consists of martensitic stainless steel AISI440B (DIN X90CrMoV18), which is a martensitic steel with relatively high content of carbon in amount of 0,9%, 18% chrome, 1,1% molybdenum, 0,1% vanadium and max. 1,0% silicium and mangane. Martensitic steel is magnetic, and mechanical properties thereof may still be improved by appropriate thermal treatment, i.e. by quenching and annealing.

In addition to said thermal treatment, the piston may also be chrome plated, wherein the chrome is deposited onto the surface by means of electrolysis. Temperature during such deposition of chrome is approx. 50°C, so that micro structure and dimensions of products may not be changed. Hard-chrome plating is recommended when abrasiveness and mechanical wearing might occur, and where anti-corrosion protection and smoothness of surfaces is required. Thickness of deposited chrome layer can be from 5 micrometers up to 1 mm or even more, and the presence of hard chrome leads to improvement of resistance against wearing, high hardness 64 HRc i.e. 1 100 HV, excellent anti-corrosion protection, chemical resistant surface, resistance against high temperature, law friction coefficient as well as to excellent adhesiveness to materials. Moreover, additives can also be mixed to pure water as a hydraulic liquid, which are selected from the group consisting of ethanol and ethylene glycol. Whenever the hydraulic apparatus with the integrated pump according to the invention is intended to operate at temperatures below the freezing temperature of water, then a mixture of water and anti-freezing additive is used instead of pure water, wherein said anti-freezing means is selected from the group consisting of e.g. ethanol C ₂ H ₅ OH in ethylene glycol C ₂ H ₄ (OH) ₂ .