Self-aligning Poppet
Mechanical and Fluid Systems
Self-aligning Poppet (MFS-TOPS-116)
Reduce valve leakage by three orders of magnitude
Overview
As NASA plans for manned missions to Mars, efforts are being made to identify technologies that must be improved to make such trips feasible. Valves have been identified as one technology in need of improvement – on the voyage to Mars, propellants and other stored materials will leak through seals in the lines, tanks, and valves. For example, traditional valve technologies are projected to result in a loss of 17 tons of hydrogen during a 6-year manned trip to Mars. Thus, to make a Mars mission (or other long duration manned space missions) feasible, cryogenic valve leakage rates must be reduced by several orders of magnitude.
After identifying this need, engineers at NASA’s Marshall Space Flight Center set out to develop a solution. The result is NASA’s self-aligning poppet for low leakage valves – a seat alignment technology that eliminates the need to precisely control interfaces between poppet sealing surfaces and the valve seat seal. Instead, the seat and poppet self-align, ensuring the poppet is always centered, parallel to the seat, and perpendicular to the actuator line of action. Testing has shown that NASA’s self-aligning poppet reduces leakage in aerospace cryogenic valves by three orders of magnitude.
The Technology
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).
Benefits
- Low leakage: Testing has shown that NASA’s self-aligning poppet reduces valve leakage rates by ~3 orders of magnitude relative to conventional aerospace cryogenic valves, resulting in near-zero (~1 SCIM) leakage.
- Reduced size, weight, and power: The self-aligning poppet greatly reduces the energy required to make a tight seal, which decreases actuator size, weight, and power.
- Scalable: NASA’s poppet has been incorporated into valves with 1” to 8” line sizes. However, the invention could be scaled down to line sizes under 1” for applications requiring smaller valves.
- Potentially reduces valve cost: While NASA’s self-aligning poppet is slightly more complex than conventional poppets, the self-aligning feature greatly relaxes required tolerances for the valve system, which may significantly reduce valve cost.
- Maturity level: Full-scale prototypes have been tested in cryogenic systems, subjected to thousands of cycles, and remain fully operational.
Applications
- Aerospace cryogenic valves
- Cryogenic valves
- Petrochemical valves
- Plug-type valves (e.g., globe valves)
Similar Results
Low-Cost, Long-Lasting Valve Seal
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.
Cryogenic Hydraulically Actuated Isolation Valve
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.
Pilot Assisted Check Valve for Low Pressure Applications
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.
Cooperative Service Valve for In-orbit Cooperative Satellite Fueling
The CSV replaces a standard spacecraft Fill and Drain Valve to facilitate cooperative servicing. The CSV offers various advantages over standard service valves: a robotic interface, three individually actuated seals, a self-contained anti-back drive system, and built-in thermal isolation. When mounted to a spacecraft as designed, the CSV transfers all operational and induced robotic loads to the mounting structure. An anti-back drive mechanism prevents the CSV seal mechanism from inadvertent actuation. Alignment marks, thermal isolation, and a mechanical coupling capable of reacting operational and robotic loads optimize the CSV for tele-robotic operations. Unique keying of the mating interface prevents mixing of media where more than one configuration of the CSV is used. Color-coding and labels are also used to prevent operator error.
The CSV has four configurations for different working fluids, all with essentially unchanged geometry and mechanics.
Miniature Separable Fill & Drain Valve
The Miniature Separable Fill & Drain Valve consists of two halves (ground and flight). The flight half is attached to the vehicle (i.e., CubeSat), and the ground half can be inserted into the vehicle in the same port as the flight half, connecting the two halves together. In normal state, the flight half seals the flow path. When the ground half is connected, the flow path is opened, allowing connected ground support equipment to supply fluid through the valve. The valve is manually operated.
There are redundant seals to eliminate leakage around the valve, including NASA's previously-patented Low-Cost, Long Lasting Valve Seal design (Patent No. 10,197,165; see MFS-TOPS-71 in the Links section of this flyer for more information) on the flight half. This eliminates the need for a swaged assembly process and the additional hardware and equipment that are typically required in conventional, elastomeric valve seat installations. The design also includes a cap for the flight half to ensure there is no leakage in flight configuration.
The Miniature Separable Fill & Drain Valve has been prototyped and provides valuable benefits for CubeSat applications. The valve could also have applications in the industrial processing industry where low flow devices are commonly used. The design is also scalable to larger applications where the removal of the actuation device would be desired.
