Composite variable oil pressure relief and compressor unload valve assembly

Claim 2

In an axial screw compressor including: a housing defining a working chamber carrying a pair of intermeshed screws for compressing a working fluid from a lower intake pressure to a higher discharge pressure with thrust forces being created within said screws during compressor operation, oil pressure thrust balancing means acting on said screws and pump means responsive to compressor operation for supplying pressurized oil to said thrust balancing means, the improvement comprising: a valve assembly including means responsive to compressor discharge pressure and compressr oil pressure for automatically unloading said compressor during compressor start up, automatically unloading said compressor upon reduction in compressor oil pressure below a predetermined minimum value after start up, and automatically preventing the compressor oil pressure from rising above a predetermined maximum value during compressor operation.

Claim 3

The axial screw compressor as claimed in claim 1, wherein said means is responsive to variation in the pressure difference of the working fluid between compressor intake and discharge for automatically varying the compressor oil pressure.

Claim 4

The axial screw compressor as claimed in claim 1, wHerein said means is responsive to variation in the pressure difference of the working fluid between the compressor intake and compressor discharge, for inversely varying the compressor oil pressure.

Claim 5

The axial screw compressor as claimed in claim 1, wherein said axial flow compressor includes a working fluid bypass passage connecting the discharge side of the compressor to the intake side, said valve assembly includes a shiftable valve member, said valve member being operatively positioned with respect to said bypass passage and said pressurized oil such that the compressor discharge pressure tends to move said valve member to compressor unload position, and said compressor oil pressure tends to move said valve member to compressor load position, and said valve assembly further includes spring biasing means tending to move said valve member to compressor unload position in the absence of compressor oil pressure.

Claim 6

The axial screw compressor as claimed in claim 1, wherein: said compressor includes a bypass passage fluid connecting said discharge and intake sides of said compressor, and said valve assembly comprises: a valve block including an elongated bore, a cylindrical main piston slidably and sealably positioned within said bore and having one end in a first position closing off one end of said bypass passage to load the compressor with the compressor discharge acting on that end of the piston when in valve closed position, means subjecting the other end of said piston to said pressurized oil for maintaining said main piston in said first position and spring means acting on said main piston in opposition to said oil pressure to shift said piston to a second position within said bore to permit said discharge passage to be in fluid communication with the compressor intake, whereby; upon loss of oil pressure or during compressor start up, said spring means maintains said piston at said second compressor unload position.

Claim 7

The axial screw compressor as claimed in claim 3, wherein: said compressor includes a bypass passage fluid connecting said discharge and intake sides of said compressor, and said valve assembly comprises: a valve block including an elongated bore, a cylindrical main piston slidably and sealably positioned within said bore and having one end in a first position closing off one end of said bypass passage to load the compressor with the compressor discharge acting on that end of the piston when in valve closed position, means subjecting the other end of said piston to said pressurized oil for maintaining said piston in said first position and spring means acting on said main piston in opposition to said oil pressure to shift said piston to a second position within said bore to permit said discharge passage to be in fluid communication with the compressor intake, whereby; upon loss of oil pressure or during compressor start up, said spring means maintains said piston at said second compressor unload position.

Claim 8

The axial screw compressor as claimed in claim 5, wherein said main piston is centrally bored to fluid connect said bypass passage with the pressurized oil acting on the end of said piston opposite that subjected to compressor discharge, and said valve assembly further includes an oil pressure relief valve carried by said piston for closing off said bore, whereby the oil pressure is maintained below a certain predetermined maximum value by bleeding off compressor oil into the compressor discharge.

Claim 9

The axial screw compressor as claimed in claim 5, wherein; said main piston is centrally bored and counterbored, to effect fluid communication between respective ends of said piston, a ball of a diameter less than the counterbore but greater than the bore is carried within said counterbore, said counterbore is axially threaded, a hollow screw is threadably received by the threaded counterbore, and a coil spring is axially compressed between the ball and the screw to permit setting of said valve to a predetermined maximum desired oil presSure.

Claim 10

The axial screw compressor as claimed in claim 5, wherein; said main piston is hollow for placing the ends of said piston in fluid communication, an oil relief valve plunger is slidably and sealably positioned within hollow main piston, a floating piston is slidably positioned within said main piston, a calibration compression spring is positioned coaxially between said floating piston and said plunger to bias said plunger and floating piston in opposite directions, a power spring is positioned between said floating piston and the main piston end wall remote from said plunger for biasing said plunger and said floating piston in a common direction to close off fluid communication between said main piston ends, and said valve assembly includes means permitting the working fluid pressure differential between the compressor inlet and the compressor discharge to act on the floating piston and to thereby control the extent of compression of said calibration spring, whereby the maximum oil pressure permitted by said oil relief plunger varies inversely with the working fluid pressure differential across the compressor.

Claim 11

The axial screw compressor as claimed in claim 9, wherein said main piston includes means defining an annular chamber at the end of said piston remote from said plunger, said floating piston includes a tubular wall portion slidably received within said annular chamber, and said main piston includes means permitting compressor working fluid discharge pressure to act on one end of said floating piston tubular wall portion to compress said power spring, and said main power piston further includes means for fluid communicating the compressor working fluid intake with said annular chamber to permit the compressor inlet pressure to act on the other end of said tubular wall portion of said floating piston and in conjunction with said power spring.

Claim 12

The axial rotary screw compressor as claimed in claim 10, wherein said power spring comprises a coil spring carried by said annular chamber having one end in contact with the end of said main piston, and the opposite end in contact with said floating piston tubular wall portion.

Claim 13

The axial screw compressor as claimed in claim 1, wherein; said compressor housing section carrying said intermeshed screws is bored axially the length of the same to define a bypass passage, a valve block is fixed to the inlet end of said axial screw compressor housing section and includes means defining a compressor working fluid intake passage, said block includes a bore coaxial with the bypass passage, acts as an extension of the same and intersects said compressor inlet, a main piston is slidably and sealably carried by said bore within said valve block and includes means for shutting off the end of said bypass passage in a first position but permitting fluid communication between said bypass passage and said compressor intake passage when in a second position, spring means coupled to said main piston acts to move said main piston to compressor unload position, means directs compressor oil to the end of said main piston remote from said bypass passage for producing a force in opposition to said springs and the compressor discharge acting on the opposite end of said main piston, said main piston is bored and counterbored to define a fluid passage connecting the ends of the same, means define an annular cavity within said main piston, a floating piston including a tubular portion is slidably and sealably received within said annular cavity, means permit compressor discharge to act on one end of said tubular portion of said floating piston, means fluid communicate the compressor intake to said annular chamber to permit the working fluid at the compressor inlet pressure to act on the other end of said floating piston, a power compression coil spring is coaxially carried within said annular cavity to bias said floating piston away from said fluid bypass passage end of said main piston passage, a plunger is slidably carried by said Floating piston and adapted to seat within said bore and acts as a pressure relief valve, and a calibrating compression coil spring is concentrically carried by said plunger with one end in contact with the same and the other end abutting said floating piston, whereby at high compressor working fluid pressure differential, said floating piston compresses the power the to lower the biasing force acting on the plunger and thereby relieve the oil pressure at a relatively low pressure value, while at low working fluid pressure differential between the compressor intake and compressor discharge, the power spring forces the floating piston to compress the calibrating spring and increase pressure at which the oil pressure relief valve operates and to thereby effectively control oil pressure thrust compensation in terms of the axial thrust forces on the compressor screw resulting from operation of the compressor.

Claim 14

The axial screw compressor as claimed in claim 12, wherein said main piston comprises first and second cylindrical members including spaced concentric tubular wall portions coupled at the end closest to said bypass passage to define said annular cavity, and said floating piston comprises spaced inner and outer tubular wall portions coupled together by a base portion and said main piston includes a bore and two counterbores in that order and wherein the shoulder between the two counterbores defines a stop determining the maximum compression of said calibrating spring, while the end of inner tubular wall portion of said main piston contacts the base portion member coupling the inner and outer tubular wall portions of said floating piston to limit the extent of expansion of said calibrating spring compressively positioned between the floating piston and the plunger.