This innovation is a rocket purge vent design that can control and balance flow across multiple vents and across very large gas flow ranges while keeping water or other undesirable gases from entering into the vented space. When changing purge rates, this device adapts to the different flow rates to maintain a very low internal delta pressure. It provides a vent design that can withstand high winds and blowing rain without allowing water entry. With the rugged design, it can operate during all rocket operational phases, from pre-flight operations through flight. This design is useful for any device needing a one-way valve type purge or general air vent where rain and gas reverse entry must not occur.

Rockets must have a dry gas purge system to keep flammable vapors and water out of closed compartments while the rocket goes through assembly, sits on the pad ready to launch, and during actual flight. The vent system must prevent animal entry, gas back flow, and rain entry in order to protect sensitive equipment and instruments.

The device is composed of a housing configured to let rainwater drain, a plate with single or multiple holes for mounting reed valves, and optional surface-mounted mesh or honeycomb material. The purge gas flow through a given vent device can be adjusted by changing the number, size, or valve characteristics, such as stiffness, opening pressure required, etc., of the reed valves. Using different sizes of reed valves on a given vent greatly increases the operational flow range of the vent, as the smaller valves open first for low flow, and larger valves open under higher flow conditions. Different vent devices in the same system can have different tunable operational flow, enabling purge gas balancing or control so that more flow goes where needed. This vent design is passive and has no high-wear parts.

Reed valves have been used in 2-cycle engines for years. On a given reed valve, as the pressure across the device increases, the reed opens further, allowing more gas flow, which lowers the pressure differential. When configured for an effective vent valve, different individual reed valves open under different purge rates, resulting in low internal pressure and the ability to balance or limit flow in desired areas. If a strong wind blows on one side of the rocket, the high-pressure side reed valves simply close, which blocks rain or contamination entry into the purged system.

At very-low-flow purge conditions, such as storage, only one or two reed valves may be set to open. As the purge requirement increases, the purge gas flow rate increases, which opens more of the reed valves maintaining low internal pressure. If the purge gas ceases to flow, all the reed valves close, preventing water, bug, and gas entry.

This work was done by Anthony Kelley of Marshall Space Flight Center and Jeffrey Lindner of Gray Research, Inc. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it. to MFS-32857-1.


NASA Tech Briefs Magazine

This article first appeared in the September, 2014 issue of NASA Tech Briefs Magazine.

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