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Counterbalance Valves

Counterbalance valves are very important hydraulic components for holding loads and running things smoothly.
In this lesson we're going to demonstrate how they function and why we use them.
Then we'll look at how they're commonly used out in the wild!

Elevator Logic

Counterbalance valves can be compared to elevator counterweights. A heavy elevator car is tough for a motor to start and stop on its own.
Without a counterweight, raising or lowering the car is tough! The motor and drawworks have a hard time starting and controlling the load.

Elevator Without Counterweight
Elevator With Counterweight
Adding a counterweight to the same elevator system makes a world of difference! The counterweight removes much of the effort from raising and lowering the loaded car.

Adding a counterweight makes raising and lowering the elevator car easier and safer. This is very similar to how a counterbalance valve works.

Pilot Operated Check Valves

You can also control vertical loads using a check-valve-based load lock, but it is only useful for low flow applications.
If there is a considerable stroke length or if the cylinder is supporting a substantial mass, the velocity of the cylinder may be excessive and the motion may be jerky and inconsistent. The force of gravity will cause the rod of a heavily loaded cylinder to run ahead of the fluid supply.
Check valve
piloted open
Cylinder is in
free fall
Cylinder
Rod Position
Time
The cylinder is in free fall while the check valve is piloted open.
This will cause a drop in pressure on the inlet port of the cylinder until the check valve can no longer be piloted open. At this point, fluid leaving the cylinder will force the check valve closed.
Check valve closed
by spring bias and
by natural flow direction
Cylinder has
stopped abruptly
Cylinder
Rod Position
Time
The cylinder stops abruptly as the check valve slams closed.
What happens then?
Motion stops and pressure builds quickly again on the cylinder’s inlet port.

This pressure also pilots the check valve to the fully open position and high flow occurs again along with a sudden lowering motion at the cylinder.

If an orifice is used on the rod-end port of the cylinder, extend speed will be slow, and rod-end pressure may be intensified to a damaging level.

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