Shuttle valves – in hydraulic & pneumatic systems

A shuttle valve, also known as a “changeover valve“, routes a hydraulic flow from two different inlets.

In hydraulic and pneumatic systems, the shuttle valve is a key component for implementing a logic circuit. It is used to build complex control systems without elaborate electronic computing systems. This makes the circuits very robust and less prone to faults. Shuttle valves are therefore used wherever a high level of reliability is required.

Design of a shuttle valve

A hydraulic shuttle valve has three ports: two inlets and one outlet. Switching from one inlet to the other occurs automatically via an internal ball. The pressurized side pushes the ball toward the other inlet, thereby blocking it.

Applications of shuttle valves

When used on its own, a shuttle valve only allows an “OR” circuit. This makes it particularly interesting when used in combination with a safety valve. With the “OR” circuit, one of the safety valves is always active. This makes it possible to remove the currently inactive safety valve for replacement or overhaul. The connected pressure system, for example a pressurized vessel, can remain in its current state. In addition to hydraulic accumulators, this use of a shuttle valve is particularly efficient for air-conditioning systems and is even mandatory there.

In hydraulics, shuttle valves play an important role in load-sensing circuits and inlet pressure compensators.

Advantages of shuttle valves

Shuttle valves are inexpensive and very robust. Internal wear is minimal and, with low switching frequency, practically negligible. The ball is lubricated by the hydraulic fluid itself. This gives the shuttle valve a very long service life and high reliability.

Another advantage of shuttle valves is that accidental shut-off of the supply line is not possible. This ensures that hydraulic flow is always maintained. This increases the operational safety of a hydraulic system.

By specifically controlling the inlet pressures, shuttle valves can also be used as a mixing valve. The mixing ratio of the media to be mixed can be precisely controlled by increasing or decreasing the respective media pressures. In this application, however, the shuttle valve is susceptible to abrasion and internal sticking. It must therefore be checked for proper function at fixed maintenance intervals.

Disadvantages of shuttle valves

A shuttle valve operates purely passively and cannot be actively controlled. It always opens toward the inlet side with the higher applied pressure. With pressure fluctuations, it can allow unintended flows to pass without any possibility of external intervention. The use of a shuttle valve therefore always requires additional measures to keep the pressure in the system controllable at every point. Pressure reducers, shut-off valves, bypasses, and other hydraulic measures are suitable for this purpose.

Manufacturers of shuttle valves

Shuttle valves are manufactured by all well-known manufacturers of hydraulic or pneumatic components. These include

• HAWE
• HYDAC
• FESTO
• … and many more.

They are available with all standard connections and in all common pressure ranges. Their simple design also makes it possible to manufacture shuttle valves as custom versions. This means the component can be produced for any application, including any pressure and temperature ranges. Shuttle valves are therefore very popular in critical fields such as nuclear engineering or aerospace. They offer maximum reliability with minimal maintenance effort and risk of failure. As long as it is not used as a mixing valve, it generally lasts as long as the hydraulic system’s designed service life.