BACKGROUND

Pneumatically and hydraulically operated equipment and control devices often incorporate, and are commonly interconnected to one another using, valves. Among these valves are relief valves, wherein a monitored fluid line is connected to an inlet of the relief valve, and the relief valve selectively opens to allow pressure in the monitored fluid line to vent from the monitored fluid line therethrough, through a relief valve vent opening connecting the relief valve to a vent, such as the local ambient pressure or a vent line. As a result, an overpressure condition in the monitored fluid line can be relieved. In these relief valve constructs, the relief valve commonly is connected to a spring housing, which provides a desired closing force against the fluid at pressure in the monitored fluid line to maintain the relief valve in the closed position when normal operating pressure is present in the monitored fluid line and thus preventing fluid flow form the monitored fluid line to the vent, and which force is insufficient to maintain the relief valve in the closed position once an undesirably high pressure is reached in the monitored fluid line and thus the relief valve opens to allow fluid in the monitored fluid line to flow to the vent. One such relief valve includes a piston having a shear seal element therein, the face of which faces a seal plate having a sealing face and an opening therethrough in fluid communication with the vent and commonly centered with respect to the sealing face thereof. A compressible element is present between the shear seal element and a bore in the piston within which the shear seal element is received and maintained. The compressible element is present to maintain the surface of the sealing face of the shear seal element against the sealing surface of the seal plate, the two sealing elements together forming a seal when in contact with one another and biased together, with the face of the shear seal element surrounding the opening in the sealing surface of the shear seal element. When the pressure of the fluid at the valve inlet, which is received through the inlet from the monitored fluid line and which fluid is in contact with the piston, creates a force on the piston greater than the force of the main spring holding the piston in place, the piston moves linearly to linearly move the shear seal element, and thus the sealing face thereof, past the opening in the seal plate, thereby allowing fluid to flow from the monitored fluid line and therethrough to vent. Thus, the fluid and pressure in the monitored fluid line can be relieved to the vent, and when the desired pressure is re-achieved in the monitored fluid line, the pressure of the fluid from the monitored fluid line against the piston is insufficient to maintain the piston in the retracted, vent open position, and the piston moves to again position the shear seal element over the opening in the seal plate.

Relief valves are constructed with a uni-directional seat bias, because the inlet pressure to the valve is used to bias the annular sealing face of the shear seal element against the shear plate to assist in the sealing off of the inlet pressure from the vent pressure during periods when normal pressure is present in the monitored fluid line, i.e., to maintain the sealing face of the shear seal element against the sealing surface of the seal plate in facing, sealing, contact. One issue encountered in this relief valve construct is the undesirable lifting off of the shear seal element from the seal plate occurring when the piston is in the valve closed position, which occurs as a result of an overpressure condition in the vent line causing the shear seal element to retract inwardly of the shear seal element bore in the piston. When this occurs, the sealing integrity of the relief valve is lost, and in some cases, the shear seal element can become cocked in the bore in a retracted position from the seal plate, and the shear seal element becomes resultantly seized in the piston, resulting in failure of the relief valve. One cause of such an overpressure condition is the connection of multiple valve outlets to the vent line, such that the vent line pressure can exceed the inlet pressure at the inlet to a relief valve connected thereto.

One attempt to overcome this issue is embodied in U.S. Pat. No. 6,651,696, wherein the shear seal element includes a through passage therein and thus the pressure is equal on either side of the shear seal element, even when the vent pressure is abnormally high. This can prevent the shear seal element from lifting off (i.e., backing away from), the seal plate, but the force of the sealing face of the shear seal element bearing against the sealing surface of the seal plate is insufficient to provide a reliable seal at that interface and the fluid in the monitored fluid line can leak past the sealing face of the shear seal element and the facing sealing surface of the seal plate, and thus to the vent.

Additionally, relief valves are commonly tested after their manufacture or refurbishment, to determine the inlet pressure at which the vent line will be exposed to the inlet pressure through the valve for a given spring force setting, commonly known as when the valve or seal of the valve seat “cracks” open. This testing can be performed by connecting the valve inlet to a variable pressure fluid source, raising the pressure at the valve inlet over a predetermined time period, and determining the occurrence pressure at which the seal of the valve cracks open, by the occurrence of fluid flowing through the valve vent passage or a change in the smooth rise of pressure being increased in the valve inlet, i.e., the monitored fluid line inlet. However, once the valve is installed in a fluid circuit, it becomes difficult or impossible to monitor the opening pressure of the relief valve in situ.

SUMMARY

Provided herein are relief valves wherein an overpressure condition in the vent bore has limited to no impact on valve performance, wherein a bi-directional seal is engaged between the shear seal element and a portion of the shear seal element bore. The shear seal element is received in a cross bore in the seal piston, which piston is biased inwardly of the valve body by a user settable bias spring, and the shear seal element includes an annular seal face having a first annular area, and an annular pressure leveraging face having an area at least twice that of the first annular area. Additionally, a seal element is provided surrounding the body of the shear seal element, in one aspect, in contact with the annular pressure-leveraging face of the shear seal element. The sealing element extends between the body of the shear seal element and the inner circumferential surface of the cross bore, to seal the inlet side pressure of the relief valve from the vent side pressure thereof.

Additionally, a relief valve having a mechanism to enable checking of the valve opening pressure in-situ, under valve operating ambient conditions, is provided. Here, a check valve is provided between the valve inlet and the piston of the valve, and is set to close off the inlet when the pressure in the interior volume of the valve is greater than the inlet pressure. A pumping port is provided through the body of the valve and it extends from the exterior of the valve into the interior volume thereof, on the side of the check valve opposite that of the inlet. A plug is normally maintained in this pumping port. However, to check the opening pressure of the valve, the pumping port plug is removed, and a variable fluid source is attachable to the pumping port to elevate the pressure in the inner volume of the valve to a value exceeding that of the check valve closing pressure vis a vis the inlet pressure, and to continue to raise that pressure to a pressure sufficient to cause movement of the piston to “crack” open the seal of the valve. The pressure being supplied into the valve interior volume is monitored to determine the pressure at which the valve opens in situ, and may be used to adjust the spring force on the piston to change the opening or “cracking” pressure of the valve, after which the opening pressure may be again checked by pumping fluid inwardly through the pumping port, which can be repeated until a desired opening pressure is achieved and the relief valve is thus properly calibrated.

