Flow control valve

Table of Contents

Symbol - Flow control valve

The flow control valve is used for load-independent control of the volume flow. That means that the speed of a cylinder or the rotational speed of a hydraulic motor can be kept constant even under different load. Let´s explain the function:

Hydraulics - Flow Control Vale - how it works, Animation

In order to keep the volume flow constant, the hydraulic pressure drop at the throttle Δp = p2 -p1 must be constant. The condition Δp = constant is fulfilled when the volume flow also is constant. With a changing load on the actuator, the control piston shifts and thereby reduces or increases the opening degree for the volume flow.

Example: If the load on the motor increases the pressure p₂ increases immediately. Via the control line the pressure on the area A₂ rises accordingly. As a result the control piston opens and thus counteracts a decrease in the volume flow.

As the flow rate increases, so does the pressure p₁ and the pressure drop Δp remains constant because the control piston has stabilized to the new load.

Review the control position in balance:

F₁ = F₂

A₁ * p₁ = A₂ * p₂ + F_spring

Because A = A₁ = A₂ we can simplify:

A * p₁ = A * p₂ + F_spring

A * p₁ - A * p₂ = F_spring

A (p₁ - p₂) = F_spring

p₁ –p₂ = Δp = F_spring/A

=> Δp is independent of p₁or p₂!

Work order: Hydraulic motor speed control with a flow control valve

Hydraulic flow control valve application

Hydraulic bridge rectifier / Flow Rectifier Circuit

If the volume flow should be adjusted in both directions independently of the load, a "trick circuit" can be used to find a cheaper solution. The disadvantage here is that the extension speed and the retraction speed of the cylinder cannot be set independently of one another.