Pilot Assisted Check Valve for Low Pressure Applications

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.

NASA's Magnetically Damped Check Valve invention is a damping technology for eliminating chatter in passive valves. Because valve failure in space missions can cause catastrophic failure, NASA sought to create a more reliable check valve damper. The new damper includes the attachment of a magnet to the poppet in a check valve to provide stabilizing forces that optimize flow and pressure conditions. Test results have proven that the Magnetically Damped Check Valve offers substantial benefits. The Magnetically Damped Check Valve works over a wide range of flow dynamics and eliminated chatter under all flow conditions tested, allowing valves to operate under various flow rates and pressures without a risk of degradation or total destruction from chatter. This technology could provide a more simple and cost-effective solution for valve manufacturers and system designers than solutions currently available in the market. Applications for the new valve include use in aerospace or industrial processes. NASA's damping technology was originally designed for check valves, but could also benefit pressure regulators, relief valves, shuttle valves, bellows sealed valves or other passive valves.

The innovation was developed for low-pressure pneumatic testing of a vacuum chamber in the Kennedy Cryogenics Test Laboratory. Standard relief valves that utilize mechanical springs did not function adequately at the low pressure (16 pounds per square inch [psi]) required by the inventors during testing. The technology is an improvement over current pressure relief valves using spring mechanisms. Typical pressure relief valves are normally held closed by a spring. After a relief valves cracking pressure is reached, the spring is compressed and the valve opens to relieve excess pressure. The NASA valve eliminates the need for a spring by instead incorporating magnets to hold the poppet relief valve in the closed position. The use of magnets in a pressure relief valve exploits the exponential decay of the magnetic field between two magnets as they are separated. This leads to a faster acting valve that does not require an increasing force to open the relief valve after cracking pressure has been surpassed, as is the case in standard pressure relief valves.

The valve consists of two major sub-assemblies: the actuator and the flow cavity. The actuator is preloaded to 1,250 N by adjusting the preload bolt, pressing the Terfenol-D against the now-deflected belleville springs. When actuation is needed, either solenoid coil is charged in a pulsed mode, causing magnetostriction or elongation in the Terfenol-D which deflects the belleville spring stack, supplying an increasing load to the stem until the parent metal seal is fractured. Once fractured, the spring inside the bellows drives the bellows base downward, onto a raised boss at the top of the fracture plate. When fracture has occurred, the stem and its spring stack is left, separated from the actuator column. The Terfenol-D is unloaded and returns to its original length. The valve remains open due to the spring inside the bellows.

Without improvements in valve technologies, propellant and commodity losses will likely make long-duration space missions (e.g., to Mars) infeasible. Cryogenic valve leakage is often a result of misalignment and the seat seal not being perpendicular relative to the poppet. Conventional valve designs attempt to control alignment through tight tolerances across several mechanical interfaces, bolted or welded joints, machined part surfaces, etc. However, because such tight tolerances are difficult to maintain, leakage remains an issue. Traditional poppets are not self-aligning, and thus require large forces to “crush” the poppet and seat together in order to overcome misalignment and create a tight seal. In contrast, NASA’s poppet valve self-aligns the poppet to the valve seat to minimize leakage. Once the poppet and seat are precisely self-aligned, careful seat crush is provided. Owing to this unique design, the invention substantially reduces the energy required to make a tight seal – reducing size, weight, and power requirements relative to traditional valves. Testing at MSFC showed that NASA’s poppet reduces leakage rates of traditional aerospace cryogenic valves (~1000 SCIM) by three orders of magnitude, resulting in leakage rates suitable for long-duration space missions (~1 SCIM). NASA’s self-aligning poppet was originally targeted for aerospace cryogenic valve systems, especially for long-duration manned space missions – making the invention an attractive solution for aerospace valve vendors. The invention may also find use in the petrochemical or other industries that require sealing to prevent critical or hazardous chemicals from leaking into the environment. Generally, the invention may be suitable for any application requiring low-leak and/or long duration storage of expensive or limited resource commodities (e.g., cryogenic gases, natural gas, nuclear engines, etc).