Search

Check valves are traditionally designed as a simple poppet/spring system where the spring is designed to equal the force created from the sealing area of the valve seat multiplied by the cracking pressure. Since the valve seat diameter in these types of valves are relatively small, less than 0.5 inches diameter, a low cracking pressure required for back pressure relief devices results in a low spring preload. When sealing in the reverse direction, the typical 20 psid storage pressure of the cryogenic fluid is not enough pressure force to provide adequate sealing stress. To better control the cracking pressure and sealing force, a bellows mechanism was added to a poppet check valve (see Figure 2). The bellows serves as a reference pressure gauge; once the targeted pressure differential is reached, the bellows compresses and snaps the valve open. Prior to reaching the desired crack pressure differential, the bellows diaphragm is fully expanded, providing sufficient seal forces to prevent valve flow (including reverse flow) and undesired internal leakage. Room temperature testing of cracking pressure, full flow pressure, and flow capacity all showed improvements. The overall results of the test proved to be 10-20 times greater than conventional check valves with no internal leakage at three different pressure differentials.

NASA's technique simplifies the seat installation process by requiring less installation equipment, eliminating the need for unnecessary apparatus such as fasteners and retainers. Multiple seals can be installed simultaneously, saving both time and money. NASA has tested the long-term performance of a solenoid actuated valve with a seat that was fitted using the new installation technique. The valve was fabricated and tested to determine high-cycle and internal leakage performance for an inductive pulsed plasma thruster (IPPT) application for in-space propulsion. The valve demonstrated the capability to throttle the gas flow rate while maintaining low leakage rates of less than 10^-3 standard cubic centimeters per second (sccss) of helium (He) at the beginning of the valves lifetime. The IPPT solenoid actuated valve test successfully reached 1 million cycles with desirable leakage performance, which is beyond traditional solenoid valve applications requirements. Future design iterations can further enhance the valve's life span and performance. The seat seal installation method is most applicable to small valve instruments that have a small orifice of 0.5 inches or less.