1. Technical Field
The present disclosure relates to a check valve, and, more particularly, to a hydraulic check valve having two seats.
2. Discussion of the Related Art
Check valves are mechanical devices used for controlling fluid flow in a system, such as a hydraulic circuit. The fluid may be, for example, a liquid or gas, such as oil or steam. Check valves control flow of the fluid in one direction, and include an inlet opening through which the fluid enters, and an outlet opening through which the fluid exits the check valve. The check valve may be used in a system for hydraulic controls, such as in the aerospace industry.
Check valves may operate automatically in a system, whereby the check valve is opened by a minimum upstream pressure caused by the fluid flow. This minimum pressure is referred to as the check valve cracking pressure. A check valve may be designed to open at a predetermined cracking pressure.
A check valve may include a spring bearing against a poppet, which provides a force on the poppet to maintain the check valve in the closed position. Once the cracking pressure is achieved, the poppet is unseated and opens, further compressing the spring. When the pressure of the flow traveling through and on the check valve decreases, for example, to less than the cracking pressure, the check valve closes to prevent further flow through the valve, and also to prevent backflow, that is, reverse flow back to the fluid source. The check valve may be installed between the fluid source and an actuator driven by the fluid flow to control the flow of the fluid between the source and the actuator.
The hydraulic system in which the check valve operates can include a relief valve. The relief valve is an over-pressure pathway designed to relieve excess pressure in the circuit, for example, excess pressure on the actuator, caused by an impact on the actuator or equipment failure. When the relief valve opens, fluid is permitted to flow through the relief valve to, for example, a hydraulic tank, so that excess pressure in the system can be relieved. Like the check valve, a relief valve poppet opens at a predetermined cracking pressure to divert fluid through the over-pressure pathway, and will re-seat upon the pressure reaching the valve's re-seating pressure. The relief valve can include a spring bearing against the poppet, which provides a force on the poppet to maintain the relief valve in the closed position.
Unwanted fluid leakage may occur in areas where the check valve poppet meets the valve body. In order to prevent this leakage, an O-ring seal can be positioned at the point of leakage. However, there is unwanted friction between the check valve poppet and the O-ring seal.
The packing seal introduces additional hysteresis which may cause the poppet to exceed its maximum cracking pressure, and excessive pressure drop at rated flow. Also, the poppet may not reseat causing excessive leakage in the reverse direction.
Therefore, a need exists for a check valve design that prevents unwanted leakage, and also prevents unwanted friction on the check valve poppet.