Design engineers of aerospace propulsion systems are always challenged with optimizing the performance of their system. As program requirements firm up, system design engineers canvass the industry to ascertain the availability of components that can improve the system performance. One of the areas for improvements are check valves.
By Louis Arcuri and Paul Meyers, Aerospace Sales and Marketing Director – Valcor
Check valves prevent the backflow of process media in hydraulic, propellant, and oxidizer systems. Check valves have a reputation as being problematic in operation. However, this is often due to misapplication of the device. It is therefore important to consider all aspects of the valve for any given application.
There are many factors to consider when sizing a check valve; using the process line size alone is not sufficient, nor desirable. Factors such as fluid temperature, pressure, viscosity, and turbidity all affect the sizing of a check valve. Based on the rigors of the application, choosing the seat material will also affect the long-term performance of the check valve. Soft vs hard seats and allowable leakage (if any) under reverse flow conditions should also be taken into consideration. In rare instances, the fast closing and opening of valves, or other downstream devices, can create a shock wave in the fluid that can trigger a check valve to chatter. In this case, a design that will protect the check valve from reacting to this shock force is required. All-welded construction eliminates the potential for external leakage, even under the most demanding shock and vibe conditions.
Chatter normally occurs in spring biased check valves when the valve poppet opens quickly and begins to oscillate against the seat. Prolonged chattering will lead to premature seat destruction and will result in valve leakage under reverse flow conditions. This leakage renders the check valve non-functional, and it must be replaced. Chatter is also frequently the result of an oversized check valve, as there is insufficient flow to keep the poppet off of its seat during normal operation. High velocity flow can also create conditions that lead to chattering. Properly sized check valves should not chatter during normal flow conditions. Still, should flows drop substantially while in service, then the check valve might chatter. A design that dampens the poppet’s movement, allowing it to move to the fully open position without rebounding, or oscillating under low flow conditions that might create the chatter, provides stable, chatter-free operation under all flow and pressure conditions.
In critical flight applications, it is often desirable to provide as much redundancy in the fluid control system as possible without compromising weight and space constraints. For example, incorporating two compact check valves in a series can be very beneficial. If for any reason one check valve is not operating properly, the other will continue to provide protection against a reverse flow condition. The redundant check valve assembly is available with an optional test port between the primary and secondary checks, enabling technicians to conduct pre- and post-flight system testing.
Check valves are used for many applications in ground-based and onboard fluid control systems, including propellant control for Reaction Control Systems (RCS) and Attitude Control Systems (ACS). Understanding how to correctly size and use a check valve can ultimately improve system performance.
ABOUT THE AUTHORS
Lou Arcuri started working for Valcor in 1980 as an Engineering Technician in the Commercial and Industrial division. He was managing the Scientific R&D lab when he was appointed Distributor Sales Manager in 1986. In 1987 he became the Sales and Marketing Manager for the Scientific division. In 1995 he left to pursue other interests, but returned to Valcor in 2016 to resume his role as Sales and Marketing Manager. Lou retired in 2017, and now works on marketing for Valcor, managing the website and creating new content for it. He also authors and contributes to many of the White Papers we post every month.
Paul Meyers has a BE in Mechanical Engineering and an MS in Technology Management from Polytechnic University of NY (now New York University Tandon School of Engineering). Paul started his career as a design engineer for major Aerospace and Space companies. The last 30 years Paul has worked in technical sales management, with nearly 20 years at Valcor Engineering Corp as Aerospace Sales and Marketing Director.
