Differential unloading

details differential unloading relief vv

Differential unloading relief valve system

Differential unloading relief valve system is used to charge the accumulator to its maximum pressure through the relief valve and hold that pressure until its required.

Relief valve comprises

The valve basically comprise a  valve spool, a differential piston, pilot valve dart and a check valve. The check valve is built in the main valve. For bigger size valves a separate plate arranged below the main valve.

Pressure unloading valve work

A differential piston  fits in a bore opposite the pilot valve dart. The piston is pressure balanced until the set pressure is reached. When unbalance the piston pushed the pilot dart and fluid pass thru it to the main spool chamber.

The hydraulic pump delivers fluid to the system via check valve and start filling the accumulator. As the pressure is equal throughout the relief valve, differential piston remains stationary and the dart and main valve spool remain closed.

When the accumulator is fully charged, the pressure cracks open the dart, lowering the pressure slightly and unbalancing the differential piston. The piston is forced toward the pilot dart lifting it completely off its seat. The main spool chamber is fill with fluid and push onto its seat the main spool, also in the same time allows fluid back to tank at low pressure.  At the same time the check valve seats to stop the accumulator discharging through the relief valve.

If system demand requires oil from the accumulator, pressure drops, and the process is repeated.

Below it can see the diagram of a differential unloading valve

Differential unloading relief diagram
Differential unloading relief valve circuit

When a machine malfunction identified the function which is not working and will be obvious which component is causing trouble.

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