Counterbalance valve simulation

This simulates a counterbalance valve on a typical hydraulic test stand.

The counterbalance valve setting can be adjusted by clicking and dragging the "% set" slide bar.

Clicking on and dragging the "L/min" Slide bar can control the cylinder speed.

The load on the cylinder can be adjusted using the grey buttons.

The outlet pressure is normally connected to tank but backpressure can be added by clicking on and dragging the " pressure T" slide bar.

Operate the directional valve to observe how the counterbalance valve can lower and hold the load, provided that the valve setting is at least 30% higher than the load pressure.

Click and drag the '% set' slide bar to adjust the counterbalance valve's setting.

The cylinder speed is controlled by the pump flow rate and can be adjusted with the 'L/min' slide Bar.

The downstream pressure (P2) is normally relieved to tank but you can experiment with different levels within this simulation.

Operate the directional valve to lower the cylinder and observe the cracking pressure in line 3.

This pressure is defined by the valve's setting, pilot pressure ratio and the cylinder area as well as the load pressure.

Experiment by adjusting the valve setting and observing how the cracking pressure changes.

The hysteresis between seat and reseat of the valve is about 85% so it is important to ensure that the valve is set approximately 30% above the maximum load pressure to ensure that the load is still supported when the valve reseats.

Reduce the valve setting until the poppet starts to open. This point is equivalent to the load value, which means you should then increase the setting to 30% above this value for reliable operation.

In order to obtain optimum stability use a low pilot ratio and a smaller rather than a larger capacity valve. The low pilot ratio will keep the pilot pressure higher, which helps stability and the smaller size of valve helps generate higher pressure drops which also helps provide greater stability. Both of these factors are contrary to the normal rules for producing a more efficient hydraulic circuit. The difference with a counterbalance valve is that by its very nature it is generating a pressure drop when working correctly.

10:1 pilot ratio valves are normally only used on stable motor circuits. Differential cylinders, variable loads and variable speeds may all result in less stable operation compared with a 3:1 ratio valve.

Click the directional valve button start lowering the cylinder and observe the pressure in line 3, then press the 'Back' key to compare this pressure when using the 3:1 pilot ratio valve.

A counterbalance valve will provide some relief protection but it is a slow acting valve with poor reseat compared to a conventional relief valve.

Increase the load on the cylinder and observe how the counterbalance valve provides a simple relief function.

If speed control is required with a counterbalance valve then a meter in flow control valve should be used.

Experiment with this circuit set-up to control the cylinder speed.

All hydraulic fluid is compressible. Long pipe lengths(volumes) between the valve and the cylinder or a large load relative to the cylinder area may result in an unstable operation.

This simulation has exaggerated fluid compressibility. Observe the slow pressure rise rate and oscillations when the cylinder stops. Reduce the load and see how the system becomes stiffer and the cylinder does not oscillate as much.

Instability can be due to air trapped between the cylinder piston and the load control valve. It is vital with cylinder applications that the circuit is correctly bled of air before operation.

Instability due to "stick-slip" on cylinder seals. If the seals used are not low friction type they will tend to cause an unstable operation which the counterbalance valve cannot correct but is likely to exaggerate.

Instability or noise due to low flow. The new design poppet and seat arrangement has eliminated noise in most applications but Sun also offers low flow rate cartridges as a possible solution.

Other potential problems not covered by this simulation include:-

a) High variable back pressure often associated with circuits using proportional valves can cause the counterbalance to go unstable. This is generally cured by using a vented valve where the spring chamber is vented separately back to the tank.

b) Decompression shock in large flow circuits when the load control is piloted open. In this type of circuit, it may be necessary to add a decompression feature as the valve is opened. Consult your local distributor to discuss possible solutions for this type of problem.

ADJUSTMENT SCREW ASSEMBLY - Compresses the main spring to change the load hold setting. C/W 'O' ring and backup seals.

LOCKING NUT - Locks the adjusting screw in position to maintain the pressure relief setting.

RETAINING CIRCLIP - Locates the spring retainer onto the poppet and holds the complete spool assembly together.

POPPET SPRING RETAINER - Locates the free flow poppet return spring between the spool and the poppet.

MAIN SPRING - Controls the load hold relief and counterbalance functions by balancing pressures at P1, P2 and P3.

SPRING LOCATION SLEEVE - Locates the spring centrally within the cartridge body.

WASHER - Locates the spool sleeve depth inside the cartridge body.

SPOOL SLEEVE- Locates the main spool and is floating to avoid cavity side load distortions. C/W 'O' ring and backup seals.

MAIN SPOOL - Controls the load hold functions. Pilot ratio is max. OD/ spool OD vs spool OD/ poppet seat. C/W 'O' ring and backup seals

POPPET SPRING - Sets the valve's free flow cracking pressure and reseats the poppet with no flow.

RETAINING WIRE - Locates the main sleeve assembly in the cartridge body while allowing radial movement to stop side loads.

CARTRIDGE BODY - The cartridge body supports internal components and allows the complete valve to be screwed into the cavity.

POPPET - The poppet provides a leak free seal against the spool end. It is stopped from moving back by the adjuster screw.