Flow Control Check Valve as a Combination of a Throttle Valve and a Check Valve

A flow control check valve is used for speed control of cylinders. The operating speed of a cylinder depends on the system pressure and flow rate of the hydraulic system. Since hydraulic systems often provide large volumes of flow, the operating speed of cylinders without throttling is often too fast. To enable slower movements, throttling is used as a cost-effective method.

Operation of a Flow Control Check Valve

A throttle valve consists of a simple passage whose media path can be reduced by a transverse barrier. Screw valves are mostly used for this purpose. However, there are also throttles that operate on the principle of ball valves. The narrower the line becomes, the less volume flow can pass unhindered, and the operating speed of the cylinder slows down accordingly. However, the pressure before the throttle increases, which results in an increased energy demand for the system.

Disadvantage of Simple Throttling Without a Flow Control Check Valve

If a hydraulic cylinder is connected to the system only with a throttle valve, it always has the same speed when extending and retracting. Depending on the application, this can be disadvantageous. It is often more beneficial for performance and productivity if a pressure cylinder quickly returns to its initial state after a slow working movement. These are the situations in which an additional check valve is installed.

Principle of the Flow Control Check Valve

The check valve offers almost no resistance to the volume flow as long as it moves in one direction. The hydraulic oil pushes open a flap in the direction of flow and keeps it open by its pressure. However, when the volume flow moves in the other direction, the pressure on the flap decreases, and it is acted upon by force from the other side – it closes. The oil now has no other way but to flow through the throttle valve.

Combination of Throttle Valve and Check Valve

It is always possible to install throttle valves and check valves separately. However, this is quite cumbersome and inefficient. Since both types of valves are frequently needed, the flow control check valve was developed. It combines both functionalities in a single component. This significantly contributes to the efficiency and safety of the system. Instead of four connection lines for two separate valves, flow control check valves only require two connection lines. Furthermore, its monolithic design is safer against leaks and easier to install.

Defects in the Flow Control Check Valve

A defective flow control check valve quickly becomes noticeable through unusual cylinder movement. Usually, in a defective valve of this type, the return flap has initially broken off. This can happen during particularly high and rapid load changes if a valve of inferior quality has been installed. Leaks in a flow control check valve are rather rare but can also occur after a certain number of operating hours. Depending on the quality of the valve, this can be remedied by changing the seals.

Extensive Control with 4/2-Way Valve

If a double-acting cylinder is connected on both sides to a flow control check valve and both are combined with a 4/2-way valve, an efficient control option is achieved: the volume flow can be adjusted differently in both flow directions – without changing the rotation direction of the hydraulic pump. With this combination of directional control valve and flow control check valves, very fast reaction times are achieved, which nevertheless remain controllable.