Pressure Compensated Flow Control Valve

Pressure compensated flow control valves are all around us, and they are incredibly useful.
We'll explain the purpose of a pressure compensated flow control (PCFC).
We'll review some basic hydraulic principles about pressure and flow.
And then we'll be ready to study a typical PCFC and learn what's actually going on inside!

What It Looks Like

PCFC valves are widely available. Here are a few we've seen from various manufacturers.






The pressure compensated flow control has its own ANSI and ISO schematic symbols.



A World Without Pressure Compensated Flow Controls

The Acme Anvils Factory Floor

The Acme Anvils factory uses a simple hydraulic motor, powered by a gear pump, to move anvils along the factory floor.

Even Load

The anvils are showing up in a regular pattern, which produces a relatively even load on the motor.

Smooth Motion

The motor is turning smoothly, causing the conveyor to move at a steady, if somewhat speedy, rate.


The relief valve is mostly closed - the load isn't enough to fully open it.


F1 and F2 prove that all of the pump output flow is making it to the motor.


Pressure varies a bit as the load on the conveyor changes between 3 and 4 anvils.

Looking for controls? Don't bother - there's nothing to control here. If the pump is running, the system is operating at a fixed rate.

This system works pretty well, as long as

  • an operator never needs to change the motor speed.
  • the load remains constant.

Speed Control

As we saw in Flow Control Fundamentals, adding a simple needle valve to serve as a flow control will let us regulate the motor speed.

Flow Control

Use the slider to restrict flow to the motor.

Motor Speed Control

Motor speed is adjusted using the Flow Control interactive slider to change the needle valve setting.

If the needle valve is backed all the way out, for maximum speed, it no longer has an effect on the system. (It will turn grey to remind you of this.)

Dialling it in/decreasing the speed will produce more and more effect.

Escape to Tank

Flow that can no longer make it to the motor escapes through the relief valve and back to tank.


What if the load isn't the nice, steady, evenly spaced parade of anvils we've seen so far? What if the anvils are showing up unevenly, instead?

Uneven Load

The anvils are appearing in clumps, which causes an uneven load on the motor.

Uncontrollable Speed

No matter where you set the needle valve, the conveyor will still race when it's lightly loaded, and crawl when it's heavily loaded.

Racing & Crawling

The motor rpm confirms that the speed of this conveyor is all over the place.

When the load is uneven, the system becomes erratic.
We need a solution that limits the motor to a steady pace, no matter what happens with the load.

This is just a preview!

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