Normally-closed (NC) Zero Leak Valve

The nitinol-actuated Normally Open Valve Assembly (NOVA) is a type of zero-leak permanent isolation valve designed for liquid propellant service on in-space propulsion systems with operating pressures less than or equal to 500 psia. The NOVA is a drop-in replacement for the currently used pyrovalve. Prior to actuation, the valve allows propellant flow with a pressure drop of < 3 psi at a flow rate of 0.15 kg/s. A compressed piece of nitinol inside the valve is heated once actuation is desired, causing the nitinol to recover to its origin shape. This recovery closes the valve, creating a leak-tight seal. The valve is compatible with all storable propellants.

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.

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.

NASA's cryogenic isolation valve technology uses solenoid valves powered by direct current (DC) electrical energy to control and redirect the energy stored in the upstream line pressure. Powering the solenoid valves only requires a DC power source capable of supplying 22 watts that can be distributed and controlled in an on/off manner. By achieving actuation using only upstream line pressure and a 22-watt DC power source, many additional support systems that are required for electromechanical and pneumatic actuation are eliminated. This reduction of parts results in several benefits, including reduced footprint, weight, and potential cost of the valve in addition to lower energy consumption. NASA fabricated several operational prototype valves using this technology for a rocket company. The table below shows the results of tests performed on these valves under cryogenic conditions. Please contact the NASA MSFC Technology Transfer Office for additional information.

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.