What is double-check valve?
Double-check valves are used to direct air flows from either of two sources into a common line, depending on the higher pressure.
They can be used to direct air flow for specific functions or to select as a source of supply the higher pressure of either of two air sources.
There are basically two types of double check valves; shuttle valves and Disc valve both carry the same functioning but the only difference is that the shuttle type has a movable shuttle to seal off the lower pressure source, whereas the disc type has a movable disc.
Working of Double-check valve:
When air under pressure reaches either end of the double check valve (inlet port), the moving shuttle or disc responds to the pressure and seals the opposite port if it is greater than the other.
The air flow continues through the double test valve’s distribution port. If the stress rates are reversed, the shuttle or disk position will reverse. Double-check valves are designed so that the air in the exhaust mode will never be impeded by the shuttle or disk.
Shuttle valve:
Shuttle valve referred to as Double check valve is a pneumatic OR valve. The valve is made up of a valve body and a synthetic ball or cuboid valve element that moves inside the valve boom.
As shown in above picture shuttle valve has two 12 and 14 outputs and a 2 output. If the compressed air applied to input 12, the ball seals off the other input 14 and the compressed air flows from input 12 to output 2 When the compressed air applied to input 14, the ball seals off the other input 12 and the compressed air flows from input 14 to output 2. When the compressed air applies to both ports, air moves from 12 to 14 or from either ports to 2.
Applications of Double-check valve:
- Use of multiple switches on one machine: more than one switch can be safely worked on one machine using the shuttle valve, and each switch can be positioned at any suitable location.
- Standby systems: If the compressor fails in an operation, the standby tank, which is controlled to be slightly below the supply of the compressor, will move the shuttle valve and take over the task. The shuttle valve shifts back when the compressor pressure is restored and seals off the standby device until it is necessary again
