Hydraulic Check Valve

Hydraulic check valves are one of the most popular type of hydraulic valve. The non-return valves or check valves are used to block the reverse flow of oil or gas in a fluid power circuit. Hydraulic check valves are also referred as non-return valves. They allow flow in one direction when installed in pipeline systems. They are operated entirely by reaction to the line fluid. Additionally these check valves may be used for pressure control or directional control.

Parts of Hydraulic Check Valves

The design and construction of a check valve makes it one of the simplest fluid power components. The hydraulic check valve consists of a valve body with inlet and outlet ports and an internal movable member biased by the spring. The movable member can be a flapper or a plunger but most often in valves of hydraulic systems, it is a ball or poppet. They are built to provide free flow in one direction and a check in the other direction and prevent flow-back in hydraulic systems.

Types of Hydraulic Check Valves

Hydraulic check valves are of several styles: swinging disc, ball, plunger, and poppet. Check valves of the pilot-operated type are also popular. The connection at the bottom is connected to a remotely operated pilot valve, As in the ordinary check valve, free flow is permitted in one direction when the line pressure lifts the plunger thus opening the valve. The flow is checked in the opposite direction until pilot pressure is applied to the blind end of the plunger through the pilot connection. This causes the plunger to unseat the valve spool and oil is allowed to flow through the valve.
When system pressure at the check valve inlet port is high enough to overcome the biasing spring force on the poppet, the poppet is pushed off its seat allowing oil to flow through the valve. This is known as the check valve's free flow direction. When the fluid attempts reverse direction of flow, the spring pushes the poppet back on the seat to block flow through the valve. Check valves can be direct acting or pilot operated. A pilot operated version is used where the no-flow characteristic of the valve is desired only for a portion of the system cycle. A pilot operated check valve also allows free flow from its inlet port to its outlet port just as in an in-line check valve.

Function of Hydraulic Check Valves

Though simple, its use can make the system sophisticated. By application of check valves one can also design many sophisticated circuit diagrams where a constant flow can be maintained in both directions by using them in a bridge. There are a number of functions of hydraulic check valves:

• Protection of the hydraulic equipment that can be damaged by reverse flow.
• Check the pressure surges conneted with hydraulic forces. For instance, waterhammer.
• Helps in preventing flooding.
• Reverse flow prevention when the system shutsdown.
• Prevention of flow under gravity.
• Vacuum conditions relief.

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