US3523745A

US3523745A - Vent valve

Info

Publication number: US3523745A
Application number: US730463A
Authority: US
Inventors: Harold T Rich
Original assignee: Air Reduction Co Inc
Current assignee: AIRCRYO Inc A CA CORP; Airco Inc
Priority date: 1968-05-20
Filing date: 1968-05-20
Publication date: 1970-08-11
Anticipated expiration: 1987-08-11

Description

United States Patent O U.S. Cl. 417-284 Claims ABSTRACT OF THE DISCLOSURE This specification discloses a valve system for a positive displacement pump, specifically a cylinder-and-piston pump. There is a vent or relief valve for venting the clearance between the piston and the cylinder head at the end of each pumping stroke of the pump. This relief valve is opened mechanically by the final movement of the piston as the piston completes a pump stroke. The pressure in the clearance drops quickly so that the suction valve of the pump inlet can open sooner as the piston starts its return stroke; and the escaping of compressed and heated fluid from the pump clearance space reduces the quantity of warm fluid remaining in the pump chamber.

BACKGROUND AND SUMMARY OF THE INVENTION Conventional positive displacement cylinder and piston pumps operate with some head-end clearance. During the discharge stroke pressure is built up in the clearance volume and this causes a delay in the opening of the intake valve when the suction stroke starts. This in turn adversely afiects the efliciency and pumping capacity. This problem has been encountered in pumps which are specifically designed to pump cryogenic liquid. Cryogenic pumps generally utilize high pressures and are constructed so that the clearance volume is at a minimum. One such pump is described in U.S. Pat. No. 3,181,473 and was specifically designed to overcome the cavitation problems encountered in conventional pumps. The valve system which is the subject of this application further reduces the cavitation problems encountered in cryogenic pumps by venting the clearance volume and thus reducing the amount of fluid residue in said volume.

This invention provides a valve for venting the compressed fluid from the clearance space at the head end of the pump cylinder. The valve is opened during the final movement of the piston at the end of a pumping or discharge stroke of the pump. The simplest and most reliable way to control the operation of the pressure relief valve is to have the piston open the valve by direct mechanical displacement. In the preferred embodiment, the relief valve is located in the piston and centrally across the piston head where it does not interefere with centrally located discharge openings in the cylinder head or the fluid that is pumped by the piston. The construction can be rearranged to locate the relief valve in the cylinder head, but this requires changes in the delivery outlets. Also, the pump relief valve can be operated electrically through switch means that respond to the final movement of the piston toward the end of its pumping stroke.

The release of the heated compressed fluid from the clearance space permits the suction of the new fluid into the cylinder to start almost instantly as the piston begins its suction stroke, therefore, volumetric efficiency of the pump is increased.

The preferred embodiment of the invention includes in the combination a cylinder-and-piston pump with the piston reciprocating axially in the cylinder. It can be used in less conventional pumps in which the piston equivalent is a vane that moves back and forth to change the volume of a chamber between the vane and another vane or wall of a fixed housing.

If the fluid being pumped is air, the clearance space can be vented to the ambient atmosphere, but if the fluid has value or its discharge into the atmosphere is objectiontable, the venting can be back to the tank or other source from which the fluid is being drawn to the intake passage of the pump.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIG. 1 is a diagrammatic view of a pump equipped with the pressure relief valve of this invention; and

FIGS. 2 and 3 are sectional views taken on the lines 22 and 3-3, respectively, of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a pump 10 having a cylinder 12 in which a piston 14 reciprocates. The pump 10 has a cylinder head 16 attached to the head end of the cylinder 14 by bolts 18. The piston 14 has a running clearance in the cylinder 12 with the clearance suflicient to allow for thermal expansion, and there are piston rings 20 on the piston 14. Six rings are illustrated in the drawing, but the number and type of rings depend upon the pressure against which the piston is required to pump.

The cylinder head 16 has a counterbore facing the cylinder 12 and this counterbore forms a chamber 22 at the head end of the cylinder of greater diameter than the inside diameter of the cylinder 12 in which the piston 14 reciprocates. An annular inlet valve 24 is located in the chamber 22 and is held against an end face 26 of the cylinder head 16 by a compression spring 28. This spring 28 is held centered by a shoulder on the inlet valve 24 and is compressed between the inlet valve 24 and the end of the cylinder 12.

The inlet valve 24 commands an inlet passage 30 which opens through the cylinder head 16 into the chamber 22 at the head end of the cylinder. A plurality of inlet passages 30 are shown in the drawing at angularly spaced locations around the longitudinal axis of the pump. The inlet valve 24 being annular, it can simultaneously command all of the passages 30.

The inlet passages 30 are connected by tubing 32 leading to a circular manifold 34 which connects through piping 36 with a source of fluid such as a tank 38. If the pump is being used for pumping air, then the tubing 32 and its connected system of piping is unnecessary.

If the pump is used in a cryogenic system, the tank 38 will contain cryogenic liquid, such as liquid nitrogen, liquid oxygen, etc.

The cylinder head 16 has a discharge passage 44 which is preferably located on the longitudinal axis of the pump and this discharge passage is connected by suitable fittings and piping 46 with a manifold 48 to which storage tanks or cylinders 50 are connected with

valves

52 and 54 at appropriate locations in the piping system. The discharge passage 44 includes a discharge valve 58 which is urged into closed position by a spring 60 and which opens to permit the discharge of fluid from the cylinder whenever the pressure in the cylinder exceeds the effective force of the spring 60. A bushing 62 in the discharge passage screws into the cylinder head 16 to compress the spring 60 against the valve 58 and this bushing 62 can be adjusted to change the pressure of the spring 60, if vdesired. The discharge valve 58 contains grooves 59 and ports 61 which a a permit the passage of fluid through the valve during the discharge stroke.

Where the discharge passage 44 opens through the end facing 26 of the cylinder head, it divides into several diverging passage sections 66 at angularly spaced locations around a center abutment area 68 of the end facing 26.

The piston 14 has a pressure relief passage extending through it. This pressure relief passage includes a longitudinally extending portion 70 and radially extending portions 72. These radially extending portions 72 open through the side of the piston 14 at a location beyond the piston rings 20, and open into the running clearance between the piston 14 and the cylinder 12. Fluid escaping through the radially extending portions 72 of the pressure relief passage flows toward the crank end of the piston 14 and escapes from the pump through a vent passage 74. If the fluid being pumped is air, the vent passage 74 can open into the ambient atmosphere, as previously explained; but if the fluid is to be returned to the tank 38, piping 76 is provided, leading from the vent passage 74 to the tank 38.

The longitudinally extending portion of the relief valve passage 70 has a counterbore 80 which contains a pressure relief valve 82 that seats against a seat element which consists of a bushing 84 screwed into the head end of the counterbore 80. The relief valve 82 is held against the seat on the bushing 84 by a compression spring 86 compressed between the valve 82 and the end of the counterbore 80.

The means for controlling the operation of the relief valve 82, as shown in the drawing, consists of a valve stem 90, which is integral with the relief valve 82 and which has a contact face 92 on the end remote from the valve 82. The stem 90 extends through the opening in the bushing 84, but in the illustrated construction, this stern is free in the bushing 84% and the valve 82 is guided by its contact with the wall of the counterbore 80. The contact face 92 extends somewhat beyond the end face of the piston 14 when the relief valve 82 is seated against the bushing 84 and, therefore, in closed position. The force of the spring 86 is such that the relief valve 82 will remain closed during the discharge stroke until contact 92 bottoms on the area 68.

The stem 90 extends along the axis of the piston 14 so that as the piston reaches the end of its pumping stroke, the contact face 92 touches the abutment area 68 and stops further movement of the relief valve 82. Thus, the final movement of the piston 14 moves the seat on the bushing 84 away from the relief valve 82 and opens the relief valve 82 so that fluid pressure in the clearance between the face 26 of the cylinder head and the Confronting face of the piston is relieved through the bushing 84, through ports 94 in the relief valve 82, and through the longitudinal portion 70 and radial portions 72 of the pressure relief passage. This drop in pressure extends not only to the clearance between the confronting faces of the cylinder head and piston, but also to the chamber in the piston head which houses the inlet valve 24.

As the piston 14 reverses its direction of movement and starts to move away from the cylinder head, the bushing 84 moves back into contact with the relief valve 82 and the pressure relief passage is closed. A suction sufiicient to open the annular inlet valve 24 against the force of the light spring 28 develops immediately and fluid is drawn into the cylinder throughout substantially the entire length of the suction stroke of the piston.

The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

I claim:

1. A pump including a cylinder and a piston that reciprocates in the cylinder, an inlet valve that opens for entrance of fluid into the cylinder during a suction stroke, the cylinder having a delivery passage for the discharge of fluid from the pump, a check valve in the delivery passage that opens for delivery of fluid from the cylinder during a compression stroke, the piston and the head end of the cylinder having confronting faces, one of the confronting faces having a pressure relief passage therein, a relief valve that commands flow of fluid from the cylinder through the pressure relief passage, means associated with one of the confronting faces for controlling the operation of the relief valve, the other of the confronting faces having an abutment area in line with the means for controlling the operation of the relief valve for contact therewith when the confronting faces approach, close to one another at the end of each pumping stroke of the piston, said delivery passage having a plurality of openings through the face that has the abutment area and at angularly spaced locations around said abutment area, and the means for controlling the operation of the relief valve being a stem extending from the relief valve and beyond the confronting face of the element in which the relief valve is located.

2. The combination described in claim 1 characterized by the delivery passage and the abutment area being on the head end of the cylinder and the relief valve passage and relief valve being carried by the piston.

3. A pump including a cylinder and a piston that reciprocates in the cylinder, an inlet valve that opens for entrance of fluid into the cylinder during a suction stroke, the cylinder having a delivery passage for the discharge of fluid from the pump, a check valve in the delivery passage that opens for delivery of fluid from the cylinder during a compression stroke, the piston and the head end of the cylinder having confronting faces, one of the confronting faces having a pressure relief passage therein, a relief valve that commands flow of fluid from the cylinder through the pressure relief passage, means associated with one of the confronting faces for controlling the operation of the relief valve, the other of the confronting faces having an abutment area in line with the means for controlling the operation of the relief valve for contact therewith when the confronting faces approach close to one another at the end of each pumping stroke of the piston, said inlet valve being an annular valve that seats against the head end of the cylinder near the wall of the cylinder, one of said confronting faces of the piston and cylinder head having a central area that projects axially for filling a portion of the space that is surrounded by the annular valve so as to reduce the volumetric clearance of the pump.

4. The combination described in claim 3 characterized by the cylinder having a chamber at its head end of greater diameter than the portion of the cylinder in which the piston reciprocates, the annular inlet valve being located in said chamber, and a spring in the chamber urging the inlet valve toward closed position.

5. A pump including a cylinder and a piston that reciprocates in the cylinder, an inlet valve that opens for entrance of fluid into the cylinder during a suction stroke, the cylinder having a delivery passage for the discharge of fluid from the pump, a check valve in the delivery passage that opens for delivery of fluid from the cylinder during a compression stroke, the piston and the head end of the cylinder having confronting faces, one of the confronting faces having a pressure relief passage therein, a relief valve that commands flow of fluid from the cylinder through the pressure relief passage, means associated with one of the confronting faces for controlling the operation of the relief valve, the other of the confronting faces having an abutment area in line with the means for controlling the operation of the relief valve for contact therewith when the confronting faces approach close to one another at the end of each pumping stroke of the piston, said pressure relief passage being in the piston and having a portion extending generally axially of the cylinder and another portion extending generally radially and opening through the side of the piston, rings on the piston flows out of the pump.

References Cited UNITED STATES PATENTS Wright 230-22 Wainwright 230--22 McFarlane.

Calaway 230-22 Parker et a1. 1032 X 6 3,318,091 5/1967 Bader 103-2 X 3,415,441 12/1968 Kehler 23022 FOREIGN PATENTS 554,352 3/1958 Canada.

DONLEY I. STOCKING, Primary Examiner W. J. KRAUS, Assistant Examiner U.S. Cl. X.R. 417--440, 444, 559