Cryogenic refrigerator compressor with externally adjustable by-pass/relief valve

Abstract: A cryogenic refrigeration compressor which has externally adjustable in-line pressure relief valve positioned between a helium supply line and the helium return line. The valve has coaxial inlet and outlet members (46, 42) and an externally adjustable spring compression spring compression member (44), which together they define a duct (48), within which is a poppet valve (76), and a spring (64) which exerts bias against the valve to close the valve against fluid pressures. The spring (64) is compressed by rotation of the compression member (44) to vary the bias on the poppet valve (44).

Description: This invention is in the field of cryogenics. More particularly, it relates to a compressor used in a cryogenic refrigerator. In a typical compressor for a cryogenic refrigerator helium returns from a cryogenic refrigerator to a compressor pump via a helium return line. Oil is injected into the helium at the inlet to the compressor. The oil absorbs the heat of compression given off by the helium. The combined mixture of helium and oil is pumped from the compressor through a line to a heat exchanger where the head contained in the mixture is given off. The helium and oil mixture is then pumped to a bulk oil separator which separates the helium from the oil and the oil returns via a line back to the compressor. The helium travels from that separator to an oil mist separator where any residual oil mist is separated from the helium. The helium travels from the oil mist separator to an adsorber which further removes any remaining impurities from the helium. From the adsorber, the helium is then pumped via a helium supply line to the cold head of a cryogenic refrigerator such as a Gifford-McMahon cryogenic refrigerator. The helium travels through the cryogenic refrigerator and returns via the helium return line back to the compressor where the cycle is again repeated. An additional helium line lies between the helium supply line and the helium return line. Situated within this line is a differential-pressure relief valve. The line and valve are located in between the helium return line and the helium supply line. Any excess pressure which may build up in the helium supply line to the cryogenic refrigerator can be released through this line and value and shunted to the helium return line valve. The relief valve automatically opens and allows helium to travel from the supply line to the return line when the pressure fluid within the helium supply line reaches a given predetermined pre-set pressure. However, the present in-line differential-pressure relief valves must be pre-set on a test board and built into the line of a compressor since all adjustments are internal. When the compressor is placed into operation and the settings within the relief valve are not correct or not matched to the compressor, the valve must be taken off the compressor and re-set on the test board. This practice is costly and wasteful of gas and manpower. In addition, it is virtually impossible to optimize the performance of each compressor unit. US-A- 3255774 discloses an adjustable in-line relief valve of a construction similar to that of the present invention and which corresponds to the preamble of claim 1. However, the construction of the disclosed valve is such that the position of the inlet and outlet members relative to each other is fixed. This invention comprises an externally adjustable in-line pressure relief valve comprising an inlet member having an inlet port connectable to a supply line; an outlet member having an outlet port connectable to an outlet line; a compression member having a duct therein for providing fluid communication between the inlet port and the outlet port, the compression member being exposed such that it may be gripped to be rotated and thus axially translated relative to the inlet member and outlet member; a valve member axially translatable into contact with the inlet member for closing the inlet port from within the duct; and a compression spring compressed by the compression member against the valve member to force the valve member into contact with the inlet member against fluid pressures, the compression of the spring being externally adjustable by rotation of the compression member relative to the inlet member and the outlet member, characterized in that the inlet member and outlet member are translatable relative to each other and the compression member is threadedly coupled to each of the inlet member and the outlet member to join the inlet member and outlet member. The invention also includes such a valve in a cryogenic refrigerator compressor unit with an externally adjustable in-line relief valve. The externally adjustable in-line relief valve is placed in a helium line between the helium supply line and the helium return line in a cryogenic refrigerator compressor. The externally adjustable in-line valve is comprised of a coaxial inlet member, an outlet member and an externally adjustable spring compression member together defining a valve duct. Within the inlet member is a valve seat against which a valve member is pressed by a spring. The externally adjustable spring compression member is connected between the inlet and outlet members so that it can be externally adjusted by rotation resulting in axial translation relative to the inlet and outlet members changing the compression of the spring against the valve member. In this manner, the pressure settings within the valve can be adjusted externally without removing the valve from the fluid line. In a preferred embodiment, the externally adjustable in-line relief valve has a valve member which is a poppet valve. The poppet valve has a cylindrical section, a truncated cone section and an O ring. The cylindrical section of the valve defines a cavity. A spring is placed into the cavity of the valve and abuts against a retention ridge therein. The truncated portion of the poppet valve extends from the cylindrical portion of the valve. An oval groove is machined in the flat end of the exterior portion of the truncated portion. Into this groove is placed an O ring. The O ring is captured by crimping the flanges which encircle the groove. Only an amount of the O ring sufficient to seal a flat surface extends beyond the groove. The invention is described in detail below, by way of example, with reference to the accompanying drawings in which:- Figure 1 diagrammatically illustrates a cryogenic refrigerator compressor embodying this invention, and Figure 2 illustrates a sectional view of an externally adjustable relief valve of this invention The cryogenic refrigerator compressor unit 10 of Figure 1 is illustrative of a compressor unit for a cryogenic refrigerator. It shows a helium return line 12 which carries returning helium from a cryogenic refrigerator to compressor pump 14. Oil is injected into the helium at the inlet to compressor pump 14 and the oil absorbs the heat of compression of the helium as the helium is being compressed by the compressor pump. The helium-oil mixture is then pumped through line 16 to and through heat exchanger 18. The helium and oil mixture passes from heat exchanger 18 through line 20 to bulk-oil separator 22. The separated oil is returned to the compressor pump 14 via line 24. The helium is pumped from the bulk-oil separator 22 through line 26 to an oil-mist separator 28 where any remaining oil mist is separated from the helium. The helium is pumped from the oil-mist separator 28 through an adsorber 32 which further filters the helium. The helium then travels to the cryogenic refrigerator via helium supply 30. Gas line 34 supplies additional helium to the helium supply line 30 when the system is charged. Between the helium return line 12 and helium supply line 30 is line 36. Within line 36 is an in-line, externally adjustable, differential pressure relief valve 38. When the pressure of the helium within the supply line 30 reaches a certain point beyond the pressure necessary to overcome the bias against the valve, the valve opens to allow helium to flow from the helium supply line to the helium return line and thus regulate the pressure of the supply line. The relief valve 38 is so designed such that the pressure setting of the valve can be set externally. Thus, it is not necessary to remove the valve from line 36 unlike in-line relief valves of the prior art. Figure 2 is a sectional view of the externally adjustable relief valve 40. Externally adjustable spring compression member 44 is attached to both outlet member 42 and inlet member 46. Outlet member 42 and inlet member 46 have conventional means for connection to the helium lines at outlet port 54 and inlet port 74, respectively. The valve of Figure 2 is threaded at the inlet and the outlet ports and connect to the helium line by screwing, but other means such as brazing the valve ports onto the helium line may be used. Outlet member 42, compression member 44, and inlet member 46 are coaxial. Together they define an internal valve duct 48. Outlet member 42 can be attached to the compression member 44 by internal threads 50. Adjacent to internal threads 50 proximal to outlet port 54 is an O ring 56 recessed within the wall of outlet member 42. The inner circumference of the O ring extends beyond the edges of threads 50 so as to produce a seal between the O ring and the smooth, non-threaded end 52 of the compression member 44 when the compression member is screwed into outlet member 42. This sealing prevents leakage of helium. Compression member 44 contains two sets of external threads 58 and 60 such that the compression member can be screwed into both the outlet member 42 and the inlet member 46. In the middle of compression member 44 is an element onto which a wrenching device can be placed in order to turn the compression member. In this case the element is a hex nut 61 which is welded onto the compression member 44. However, the adjustment element can also be flat sections machined on the exterior of the compression member of holes drilled in the periphery of the compression member for a spanner wrench. When final adjustments are made, a lock wire-set screw or epoxy can be applied to the threads of the compression member to prevent rotation. The end of the cylindrical compression member most proximate to the outlet member contains a bore 63 which extends axially therethrough. Bore 63 expands into a cavity 62 into which a spring 64 fits. A retention ridge 65 is formed where bore 63 expands into cavity 62. This retention ridge 65 compresses the spring 64 as the compression member 44 rotates into the inlet member 46 and out of the outlet member. Inlet member 46 forms internal cavity 66 which narrows into bore 70 forming a sealing ridge 72 proximate to the inlet port 74. Within the cavity 66 is a valve member 76 which is in this case a poppet valve. A closing force is placed onto the poppet valve by the spring 64. Inlet member 46 also has internal threads 78 which enable compression member 44 to translate axially into the cavity 66. Adjacent to internal threads 78 proximal to inlet port 74 is a recessed O ring 77 within the internal surface of inlet member 46. The inner circumference of the O ring extends inward beyond the edges of threads 78 so as to produce a seal between said O ring and the compression member 44. Poppet valve 76 is comprised of a cylindrical portion 80 proximal to the outlet member and a truncated cone portion 102 which is proximal to the inlet port 74. The end of the truncated cone 102 proximate to the inlet port 74 is machined out forming a cavity 106 and flanges 108 and 110. Into this cavity is placed O ring 104. The cavity is so designed to capture about 90% of the O ring. The O ring is captured by crimping flanges 108 and 110 onto the O ring. This allows sufficient protrusion of the O ring so that the O ring can seal against a flat surface such as sealing ridge 72. The cylindrical portion 80 of the poppet valve defines cavity 114. Retention ridge 116 is formed within the poppet valve where cylindrical portion 80 of the valve narrows to form the truncated cone portion 102 of valve 76. Spring 64 is placed within cavity 114 of the poppet valve and within cavity 62 of the compression member 44. Spring 64 is compressed as compression member 44 is translated axially further into inlet member 46. The spring, in turn, exerts bias against retention ridge 116. The bias exerted against retention ridge 116 causes poppet valve 76 to be secured against retention ridge 72. This bias determines the amount of gas pressure which is required in the gas supply line to open poppet valve 76 to allow gas to flow from the supply line through the relief valve and into the helium return line. The externally adjustable compression member can be either internally or externally threaded so as to screw into the inlet member or the inlet member can screw into the compression member.

Claims: An externally adjustable in-line pressure relief valve comprising: an inlet member (46) having an inlet port (74) connectable to a supply line (30); an outlet member (42) having an outlet port (54) connectable to an outlet line (36); a compression member (44) having a duct (48) therein for providing fluid communication between the inlet port (74) and the outlet port (54), the compression member (44) being exposed (61) such that it may be gripped to be rotated and thus axially translated relative to the inlet member (46) and the outlet member (42); a valve member (76) axially translatable into contact with the inlet member (46) for closing the inlet port (74) from within the duct; and a compression spring (64) compressed by the compression member (44) against the valve member (76) to force the vlave member (76) into contact with the inlet member (46) against fluid pressures, the compression of the spring (64) being externally adjustable by rotation of the compression member (44) relative to the inlet member (46) and the outlet member (42); characterized in that the inlet member and outlet member are translatable relative to each other and the compression member (44) is threadedly coupled to each of the inlet member (46) and the outlet member (42) to join the inlet member (46) and the outlet member (42). A pressure relief valve as claimed in claim 1, further comprising a first O ring (77) between the inlet member (46) and the compression member (44) and second O ring (56) between the outlet member (42) and the compression member (44) for sealing the fluid path (48) from the inlet port (74) to the outlet port (54). A pressure relief valve as claimed in Claim 2, wherein each end of the compression member (44) is externally threaded (58, 60) in cooperation with internal threads on the respective inlet member (46) and outlet member (42), and the compression member (44) comprises a non-threaded extension beyond the threads (58, 60) at each end thereof, the first and second O rings (77, 56) being positioned between each non-threaded extension and the respective inlet and outlet members (46, 42). A pressure relief valve as claimed in any one of Claims 1 to 3, wherein the compression spring (64) is retained within the compression member (44) and abuts against a reduced interior diameter portion (116) of the compression member. A pressure relief valve as claimed in Claim 1, wherein both ends of the compression member (44) are externally threaded (58, 60) and are respectively positioned within the inlet member (46) and outlet member (42). A pressure relief valve as claimed in any one of Claims 1 to 5, wherein the inlet port (74) and the outlet port (54) are threaded for respective connection to the supply line (30) and outlet line (36). A pressure relief valve as claimed in any one of Claims 1 to 6, wherein the valve member (76) is a poppet valve. A pressure relief valve as claimed in Claim 7, wherein the portion (80) of the poppet valve (76) proximal to the outlet port (54) is cylindrical and the portion (102) proximate to the inlet port (74) is a truncated cone, within the cylindrical portion (80) of the poppet valve (76) is a cavity (114) into which the spring (64) is placed, the cavity (114) has a retention ridge (116) against which the spring (64) abuts, the truncated cone portion (102) of said poppet valve (76) contains a multiplicity of bores extending radially therethrough to the cavity (114) within the cylindrical portion of the valve, the end of the truncated cone (102) of the poppet valve (76) contains a cavity (106) with two connective flanges (108, 110) extending axially therefrom, an O ring (104) is placed within the cavity (106) and is captured into place by crimping the flanges (108,110) against the O ring (104) allowing only an amount of the O ring (104) to extend beyond the cavity (106) sufficient to seal a flat surface. A method for providing variable pressure relief on a fluid supply line, comprising connecting an externally adjustable in-line pressure relief valve (38) as claimed in any one of Claims 1 to 8, to a fluid supply line (30) and an outlet line (36), including rotating the compression member (44) as the inlet and outlet members (46, 42) remain fixed to the supply line (30) and outlet line (36). An externally adjustable in-line pressure relief valve as claimed in any one of Claims 1 to 8, in an improved cryogenic refrigerator and compressor system in which helium is carried through a helium return line (12) from a cryogenic refrigerator to a compressor pump (14) where the helium is mixed with oil and compressed, and the helium is pumped to and through a heat exchanger (18), from said heat exchanger (18) the helium and oil mixture is pumped to an oil separator (22), from which the oil is pumped back to the compressor (18) and the helium is pumped back to the cryogenic refrigerator via a helium supply line (30), a helium connecting line (36) is located between said helium supply and return lines (30, 12), and said connecting line (36) has said in-line differential pressure relief valve (38) which opens to allow helium to travel from the helium supply line (30) into the helium return line (12) if the pressure within the helium supply line (30) exceeds a pre-determined value, the valve (38) being externally adjustable while connected in the connecting line (36).

Inventors: NICOLL HARRY G, NICOLL, HARRY G.
Applicants: HELIX TECH CORP, HELIX TECHNOLOGY CORPORATION
Application year: 1987
Main classification: F16K17
IPC codes: F25B9, F16K17, F25B41