Non-return valves or check valves

Simple non-return valve

Check valves have the task to shut off the flow in one direction and allow free flow in the opposite direction within a hydraulic circuit. They are also referred to as non-return valves:

The functioning is quite simple:

Hydraulic non-return valve

The sectional view shows a check valve with a cone as a closing element which is pressed by the spring onto the seat of the housing. The pressure required to move the closure member against the spring can be referred to as the opening pressure. This depends on the chosen spring and the area of conical surface and is usually between 0.5 and 3 bar.

Application hydraulic non-return valve

Hydraulic Check Valves and their Applications

Example 1: Install parallel to a filter. Upon reaching a certain pressure (e.g. 3 bar), the oil is diverted to the filter. So the system can still work despite of a clogged filter.

Example 2: Mounting within the pump line, to protect the pump from pressure surges or to avoid oil drain due to external load on the pump.

Example 3: Instelled parallel to a throttle: Only in the direction A to B you have a throttling. In the reverse direction the check valve opens.

Unlockable non-return valve

Pilot-operated check valve with symbol

This shut-off valve can be unlocked via a pilot line in the reverse direction. The functioning is as follows:

Hydraulic unlockable non return valve

If the port A has high pressure and lthe port B low pressure, so is the valve is in the forward direction. If the pressure conditions changes (port A on low pressure), the main poppet is held by the spring and the system pressure on its seat.

By pressurizing the control port X the pilot piston pushes the main poppet off its seat. Now, the oil can also flow from B to A. They say, the valve is now "unlocked".

Note: To ensure that the locking mechanism of the pilot-operated shut-off valve also closes reliably in the middle position of the directional control valve, the control port x must be relieved. Then the spring can press the cone against its seat. In the example above, both ports (A and B) of the directional control valve are connected to the return line (tank) in the middle position.

Application: The main application is to secure and shut-off under load (for example the lifting platforms). For maximum safety and in consideration of the leakage these type of valves should be mounted close to the cylinder.

Double Pilot Operated Hydraulic Check Valve - How it works

Double Pilot Operated Hydraulic Check Valve

In order to keep an actuator in its position without leakage in both directions, two pilot-operated check valves are required. The Double Pilot Operated Check Valves contains two of these pilot-operated check valves in its housing:

Hydraulic Double Pilot Operated Check Valves - how it works

Circuit example: Double Pilot Operated Check Valve protects hydraulic motor in both directions of rotation.

... pic coming soon