Friday 9 March 2018

shuttle valve & fast exhaust valve

Posted by and on January 23, 2011

http://www.valvehydraulic.info/valve-2/hydraulic-shuttle-valves.html

A shuttle valve, also known as a double check valve, allows pressure in a line to be obtained from alternative sources. It is primarily a pneumatic device and is rarely found in hydraulic circuits.

Construction is very simple and consists of a ball inside a cylinder, as shown in Figure 4.25a. If pressure is applied to port X, the ball is blown to the fight blocking port Y and linking ports X and A. Similarly, pressure to port Y alone connects ports Y and A and blocks port X. The symbol of a shuttle valve is given in Figure 4.25b.

A typical application is given in Figure 4.25c, where a spring return cylinder is operated from either of two manual stations. Isolation between the two stations is provided by the shuttle valve. Note a simple T-connection cannot be used as each valve has its A port vented to the exhaust port.

Two-Step Speed Control System From Fluid Power with Applications By Esposito

Clamping and bending

http://www.hydraulicspneumatics.com/hydraulic-valves/so-you-think-you-know-shuttle-valves

—Valve A above applies air to the up end of the clamp cylinder through shuttle valve B. The operator then actuates valve C to extend the bend cylinder and reset valve A. Shuttle valve B maintains pressure in the clamp cylinder. When the operator releases valve C, low-pressure air from reducing valve D retracts the clamp cylinder. The pilot line of valve A is vented, and the system is ready for the next operation.

A fast exhaust valve (

-Figure 4.26) is used to vent cylinders quickly. It is primarily used with spring return (single- acting) pneumatic cylinders. The device shown in Figure 4.26a consists of a movable disc which allows port A to be connected to pressure port P or large exhaust port R. It acts like, and has the same symbol as, a shuttle valve. A typical application is shown in Figure 4.26b.

Fast exhaust valves are usually mounted local to, or directly onto, cylinders and speed up response by avoiding any delay from return pipes and control valves. They also permit simpler control valves to be used.