Veritable Aviation

How Do Drain Valves Work in Aviation?

Between the fuel, oil, and water found in the receptacles of several aircraft compartments, there is a continuous need for used fluid to be drained safely. To accomplish this, drain valves are installed at various locations throughout aircraft, including the fuel tank, oil compartment, and onboard sinks. In this blog, we will discuss how drain valves work and what considerations exist with the various fluid types they may encounter.

Drain valves are found on both airplanes and helicopters, serving a similar function and having the same design. This design consists of an o-ring attached to the valve's body by a stem. Using an o-ring, the risk of dirt, oil, and other debris gathering around the valve is greatly reduced. Prior to this design change, older fuel drain valves constantly suffered from drip caused by dirt buildup. Most drain valves are manufactured according to MS or other aviation standards, making them compatible with a wide array of aircraft.

Water drain valves connect to the used water and waste tanks from the toilets and sink compartments within aircraft. They enable maintenance and environmental management teams to quickly remove waste and other liquids to allow for regular inspection and cleaning. Generally, disposal water and waste get drained every flight by a specialized water truck.

Since oil and fuel drain valves are constantly exposed to corrosive elements with fluctuating temperature ranges, they are generally manufactured in a specialized manner with tougher materials. For example, the body and stem are made from a lightweight aluminum alloy, while the springs are usually stainless steel. Both of these materials are durable and resistant to corrosion. Oil and fuel valve drains are also equipped with a special synthetic rubber o-ring to support operations over a wide variety of temperatures, from below freezing to boiling. Additionally, these valves should withstand high operating pressures while also being flame retardant.

FAA regulations state that all valve drains must pass a series of tests before being approved. The first of these is a simple functionality test, proving that the drain valve operates as described by the manufacturer. Next, a flow test is performed to ensure that the valve can dispense a quart of fluid in under a minute. Fuel leakage tests apply varying amounts of pressure to a closed drain valve while the inspector checks for any leaks in the component. Similarly, pressurized air is applied to the valve outlet to inspect for any leakage during the air pressure test.

Other trials include resonance, cycling, and proof pressure tests. Resonance testing involves subjecting the valve to a frequency range for several hours to replicate possible vibrations during flight. In cycling trials, the tester applies fluid pressure to the inlet port while the rest of the valve is mounted on a vibration device. Even after being exposed to several vibratory cycles, the valves should remain leak-free while also avoiding any damage. Finally, the proof pressure test subjects the inlet port to a fuel pressure of around 100psi for one minute while keeping the outlet at atmospheric temperature. After this test, the inspector will assess external and internal components for any signs of damage or leaks.

When you are in need of high quality drain valves, Veritable Aviation has you covered with one of the largest ready-to-purchase inventories in the industry. Explore our numerous part catalogs or use our search engine to find the exact item you need, and keep in mind that you may begin the purchasing process at any time using our Instant RFQ service. With team members on standby for customers 24/7x365, we guarantee customized quotes within 15 minutes or less. Choose Veritable Aviation for your next project and learn how we can serve as your strategic sourcing partner.


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