Pump output check Figs 912 913 915 and 918

1 Disconnect the inlet hose which supplies fluid pressure from the pump to the control (reaction) valve, preferably at the control valve end.

2 Connect the inlet hose to the pressure gauge end of the combined pressure gauge and shut-off valve tester and then complete the hydraulic circuit by joining the shut-off valve hose to the control valve.

3 Top up the reservoir if necessary.

4 Read the maximum pressure indicated on type rating plate of pump or manufacturer's data.

5 Start the engine and allow it to idle with the shut-off valve in the open position.

6 Close the shut-off valve and observe the maximum pressure reached within a maximum time span of 10 seconds. Do not exceed 10 seconds, otherwise the internal components of the pump will be overworked and will heat up excessively with the result that the pump will be damaged.

7 The permissible deviation from the rated pressure may be ± 10%. If the pump output is low, the pump is at fault whereas if the difference is higher, check the functioning of the flow and pressure control valves.

An average maximum pressure figure cannot be given as this will depend upon the type and application of the power assistant steering. A typical value for maximum pressure may range from 45 bar for a ram type power unit to anything up to 120 bar or even more with an integral power unit and steering box used on a heavy commercial vehicle.

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