What is a Shuttle Valve? A Practical Guide by HFD Hydraulic

What is a Shuttle valve?

A shuttle valve is a kind of valve which allows fluid to flow through it from one of two sources. It is generally a pneumatic device but sometimes, it can be found in hydraulic systems. It is also a kind of a double check valve that allows pressure in a line to be accessed from alternative sources.

The shuttle is the sliding part that resides in the enclosure and its function is to seal off either one or other inlet ports. At each inlet port, there is a seat for the shuttle.

The Structure and Functions of Shuttle Valves

A shuttle valve’s basic structure consists of a tube with three openings. These openings are on each end then one in the middle. A ball moves freely within the tube. Through an opening on opening on one end, pressure from a fluid is exerted pushing the ball towards the opposite end. The action prevents the fluid from traveling through that opening, however, allows it to flow through the middle opening. 

In this way, two different sources can provide pressure without the threat of backflow from one source to another. 

In a normal operation place, the pneumatic or hydraulic supply has a free flow from the normal inlet port through the shuttle valve. And then, the flow is passed through the outlet port to the actuating unit which may be a pneumatic or hydraulic cylinder. 

The operation is very simple and consists of a ball inside a shuttle valve, as shown below figure:

1. The pressure is applied to X (inlet port)
2. The ball is blown or directed towards Y (the right side) blocking it
3. Alternate port Y is block; Ports X and A gets linked

Similarly, when pressure is applied solely to Y, it connects Y to A, while blocking X.

See reference

The ball/ shuttle/ piston continuously stays in its normal position until the alternate system is activated.

This activity channels pressurized fluid from the alternate system to the shuttle valve, then pushes the shuttle from the alternate system inlet port.

The pneumatic or hydraulic supply from the alternate inlet source can then flow freely to the outlet port but is blocked from entering the normal inlet system by the shuttle which actually blocks off the normal inlet system port.

Parts of a Shuttle Valve

Valve Body/ Housing

This is a cylindrical case housing (usually made of metal or strong plastic) the internal components. Aside from housing the internal parts, it also provides support.

Ports

These are the entry and exit points of fluids or gasses. Inlet ports are typically two ports. The outlet port is a single port. This is where the fluid or gas exits after being channeled through the valve.

Shuttle

Also known as the spool, is a cylindrical part with seals (to avoid leakages) traveling inside the valve body. The spool switches or blocks the group port diverting flows, depending on external pressure.

Seal

These are o-rings or gaskets ensuring proper sealing between the shuttle and the valve body. These sealings prevent seepage. They also ensure the continuous flow of fluid or gas especially when the shuttle is in motion.

Springs

Some shuttle valves, particularly spring-biased shuttle valves, include one or more springs to help position the ball or piston when there is no pressure from either source making the valve ready for further operation.

Shuttle Valve Application

Usage of more switches on one machine on heavy industrial machinery

With the aid shuttle valves, more than one switch can be operated on a single machine for safety, and each switch can be placed at any suitable location.

Winch brake circuit

The shuttle valve provides break control in pneumatic winch application. They direct air to open the brake shoes when the compressor is operated. Also, when the control valve is centered, the brake cylinder is vented through the shuttle valve, and the brake shoes are allowed to close.

Air pilot control

Locking of the cylinder is caused by converting air to oil. Shifting the four-way valve to either extreme position causes the application of the air pilot through the shuttle valve. At the same time holding the two air-operated valves open and applying oil under air pressure to the corresponding side of the cylinder. Meanwhile, positioning a manual valve to neutral exhausts the air pilot pressure, closing the two-way valves, and trapping oil on both sides of the cylinder to lock it in position.

Standby and emergency systems

Compressor systems and subsea applications requiring hot standby or purge gasses capability are pressure controlled by the shuttle valve. Instrumentation, pressure cables, or any system requiring continuous pneumatic input use shuttle valves. Should the compressor fail, the standby tank (regulated to slightly under the supply) will shift the valve and take over its function. However, once the compressor pressure is restored, the shuttle valve shifts back sealing off the standby system until it is needed again.

Advantages and Disadvantages

Advantages

Compact Design: They are space-efficient so they can be integrated into tight spaces within machines or systems. This saves a lot of space for industrial systems.

Reliability: Their very few moving parts contribute to high operational reliability. They offer consistent fluid or air flow control as they are very efficient components.

Bidirectional Flow: Bidirectional flow is automatically allowed by shuttle valves. This enables fluids or air to travel in either direction which depends on external environmental conditions. Bi-directional flow in shuttle valves increases flexibility when it comes to system design and performance.

Versatility: Their flexibility can serve various fluid or air control needs. They can adapt to different pressure levels and flow rates making them very reliable in various industrial settings where operational needs aren’t usually stable.

Response time: Shuttle valves have a fast response to pressure changes as well as flow changes. They also have the level of sensitivity of fast response that play a big part on applications where immediate modifications are required for maintaining efficiency as well as system disruption prevention.

Cost effective: Because of its simplicity in design, manufacturing and maintenance cost-effectiveness is achieved. Shuttle valves have fewer parts with simple construction so the production price is smaller making them commercially viable for numerous uses.

Aside from advantages mentioned above, shuttle valves serve to isolate the failed supply line if either of the dual supply ruptures or develops leakage. They also provide direct connection to functional parts.

Disadvantages

Limited Control Precision: When it comes to its simple design, accuracy may be reduced in the regulation of fluid or air to the more advanced types of valves Because of this limitation, they are less viable for those applications demanding a much more precise and fine-tuned control.

Internal leakage: The undesirable seepages of fluids or air often detected between ports (internal leakages) can occur in shuttle valves resulting in many inefficiencies. It could also be tough for systems that require accuracy in control of pathways with the necessary isolation values. Leakage takes place if the shuttle does not have a good seal (to block).

Susceptibility to Contamination: Foreign particles in the liquid can cause valve clogging or any failures. Such a system requires maintenance and regular filtration for efficiency.

Complexity in multi-port configuration: Shuttle valves with 2 to 3 ports are quite common. However, 4-port shuttle valves have increased complexity when it comes to configurations. It’s tough managing multiple pathways because it goes against the principle of flow dynamics. And different factors should be considered in understanding and designing processes. See reference

Aside from disadvantages mentioned above, if there is small leakage and it is some distance away, there may not be enough differential pressure to move the shuttle.

Now that you already have a solid background about shuttle valves, take a look at our product catalogue!

Need a quote? Send us a message!