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Pumping apparatus having a piston with a diamond-like carbon coatingRelated Patent Categories: Pumps, Expansible Chamber Type, Valved PistonPumping apparatus having a piston with a diamond-like carbon coating description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080019854, Pumping apparatus having a piston with a diamond-like carbon coating. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a pumping apparatus. BACKGROUND ART [0002] A number of pumping devices is described in the state of the art, said pumping devices being used for transfer of liquid in low- or high pressure apparatuses. Piston- or plunger pumps adapted for usage in said low- or high pressure devices comprise one or more a pistons which are arranged to perform reciprocal movements in a corresponding pump chamber, thereby compressing the fluid within said pump chambers. The reciprocation is repeated thousand fold during the lifetime of the pump, thereby causing wear, abrasion and, hence, changes of the material and surface properties to the piston. [0003] A liquid chromatography pumping system is described in EP 0,309,596 B1 to Strohmeier and Witt, e.g., depicting a pumping apparatus comprising a dual piston pump system for delivering liquid at high pressure, e.g., for solvent delivery in liquid chromatography. [0004] Further pumping systems with coated components are disclosed in the state of the art: WO 06,005,399 A1 to Beck et al. refers to an axial piston engine with a wear-resistant carbon-containing layer on one of the sliding faces. [0005] JP 2004,239,191 A2 to Kato et al. describes a hydraulic piston pump motor with a DLC (diamond-like carbon) coated film on a sliding surface of a shoe which slidably contacts said swash plate for reciprocally moving the pistons. [0006] JP 2004,019,464 A2 to Narato discloses a hydraulic piston pump motor with a piston ring being coated with a thin film of DLC on its sliding surface to improve wear resistance. [0007] DE 102,004,032,342 A1 to Fischer et al. discloses a method providing the outside extent surface of a piston ring base with a coating comprised of two layers, one of which being a wear protection layer. [0008] US 2004,258,547 AA to Bayer et al. refers to a pump piston and a sealing ring with an additionally applied coating, predominantly formed of halogen-, silicon-, carbon-containing and/or metal-organic monomers. [0009] WO 03,078,679 A1 to Teer concerns a coating and apparatus and method for its application. The coating is applied by chemical vapour deposition using a pulsed DC biased power supply, the coating having an initial metal layer followed by a transitional metal carbide layer and a DLC layer. [0010] JP 2,000,320,670 A2 to Kitago et al., a piston with a hardening layer is described, comprising a DLC layer which is applied succeeding to soft nitriding and polishing of a steel piston. DISCLOSURE [0011] It is an object of the invention to provide an improved pumping apparatus. The object is solved by the independent claims. Further embodiments are shown by the dependent claims. [0012] According to embodiments of the present invention, a pumping apparatus is described which is adapted to deliver liquids under high pressure in devices such as, e.g., devices for analysis of chemical or biochemical compounds, working with liquids or liquid samples being injected under high pressure. Said pumping apparatus is composed of one or more pistons, each of which being movably arranged in a corresponding pump working chamber. Moving of a piston is performed by a drive unit having a piston holder; accordingly the reciprocal movement of the piston in the chamber can be carried out for a plurality of strokes. Each strike provides a liquid compression; the plurality of strikes demanding an increased material resistance with respect to the piston wear. A diamond-like carbon (DLC) coating on the piston surface advantageously provides an improved wear resistance, adapted to provide a reduced abrasion of the piston. Said improved wear resistance is based on a hardening of the surface due to the coating, associated with an optimized surface smoothness and evenness leading to friction reduction. [0013] A further embodiment of the present invention comprises two pistons arranged in a dual serial or dual parallel mode in order to provide continuous pumping by performing pump cycles. Due to an advantageously provided coating of the piston surfaces, which coating reduces friction of the pistons and optimizes surface durability, an optimized performing of pump cycles can be carried out. [0014] A further embodiment refers to a high pressure liquid chromatography device to perform injecting of liquid into a chromatograph. The herein used pumping apparatus has a piston for repeated reciprocation into a pump working chamber, which piston is advantageously coated with a diamond-like carbon coating, providing a hard and even piston surface which helps prolonging the lifetime of the piston. Furthermore, the highly precise pumping of said device, which is used for injecting micro-volumes pumping, is further optimized since the piston cay move nearly friction-free. [0015] Further embodiments of the present invention refer to a high pressure liquid chromatography device comprising a liquid pumping apparatus having a DLC coated piston, which may be made of sapphire, being chemically inert and having an improved surface with respect to abrasion, and showing a reduced brittleness. DETAILED DESCRIPTION [0016] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to by the same reference signs. [0017] FIG. 1 schematically shows a pumping apparatus comprising a coated piston. [0018] In the following, generally pumping apparatuses for delivering liquid at a high pressure are described. The pressure which affects the liquid provides a noticeable compressibility of the liquid, which noticeable compression is achieved in that a piston of the pumping apparatus is reciprocated in a pump working chamber containing the respective liquid. The pump working chamber may be coupled to a valve in order to permit liquid flow unidirectional only. Driving of the piston may be performed by a drive unit which permits pressurizing of the liquid in said pump working chamber to high pressure. Advantageously, a diamond-like carbon coating covers the parts of the piston which are the most susceptible to abrasion; the smooth and even DLC coating reduces friction and damages due to friction. [0019] FIG. 1 depicts a pumping apparatus comprising a piston 1, which is reciprocated in a pump working chamber 3, having a cylindrical inner bore 9 and having an inlet port 4' and an outlet port 5'. An inlet valve 13 is connected via a capillary 5, which has an inner bore 4, to said inlet port 4' of the pump working chamber 3, to permit liquid flow only unidirectional into the pump working chamber 3. The reciprocating movements are driven by a drive unit (not shown herein), which operates the piston holder 6 via the ball 8 which is embedded in a recess 10. The ball 8 is operated by an actuator 7. Since the piston holder 6 is mounted to the piston 1, the drive unit may affect the piston 1 via the piston holder 6 to perform said moving of the piston into the pump working chamber 3. Furthermore, a seal 11 is provided for sealing off the pump working chamber 3 at the opening, through which the piston 1 moves into said pump working chamber 3, so that unwanted liquid flow-out is prevented. Guiding of the piston1 into the pumping chamber 3 is supported by the guiding element 12. [0020] The liquid in said pump working chamber 3 is compressed to a high pressure before being delivered via an outlet port 5' and via a capillary 5 with an inner bore 4 being attached to said outlet port 5', into a liquid receiving device. [0021] Generally, wear and abrasion are well known phenomena causing material destruction of a plurality of components in driving units, pumps and other devices. Since the piston 1 performs said reciprocating movement manifold during its lifetime, it is subjected to said abrasion due to friction loading, accordingly risking to be damaged from wear. Advantageously reducing of said destructive effects is achieved by optimizing the surface durability. 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