Counterbalance Valves

Objectives

  • Describe the purpose of a counterbalance valve.
  • Demonstrate how counterbalance valves function.
  • List common uses of counterbalance valves.

What Is It?

Counterbalance valves can be compared to elevator counterweights. A heavy elevator car is tough for a motor to start and stop on its own.

Raising the load
Holding the load
Lowering the load

Without a counterweight, raising or lowering the car is tough! The motor and drawworks have a hard time starting and controlling the load.

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.


Raising the load
Holding the load
Lowering the load

Adding a counterweight makes raising and lowering the elevator car easier and safer.

Pilot Operated Check Valves

A counterbalance valve works in a similar way as an elevator counterweight. Controlling vertical loads using a check valve based load lock 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

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 to the point where 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

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 gravity drop port of the cylinder, then stroke speed will always be very slow.

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