1 Click on the directional valve's solenoid to operate the valve.
2 Adjust the output motor slider to change the load resistance and note the change in power output.
3 Adjust the supply pump speed to increase the flow rate.
4 Adjust the pressure relief valve slider to set the maximum supply pressure.
5 Note how the system pressure is always set by the load unless this exceeds the pressure relief setting.
6 If the load resistance exceeds the supply pressure, the motor will not turn.
11 This open centre system is vented to tank in the standby mode.
12 Very little system pressure is generated when the pump is drained to tank.
13 Consequently, very little input power is required.
21 The closed centre spool prevents the flow going to the actuator.
22 The pump is a constant delivery unit so the flow has to go somewhere and will flow across the relief valve.
23 The relief valve is normally at the maximum pressure setting for the circuit so this will generate a great deal of power, which will transfer into heat in the oil.
24 Look at the power input and compare it to the power output.
31 A pressure reducing valve provides a constant reduced pressure downstream of the valve.
32 Activate the directional valve and set the load resistance and relief valve setting to maximum.
33 Adjust the reducing valve slide bar and observe how the downstream pressure changes.
34 If the load resistance is set to minimum, with the reducing valve at mid setting, the valve goes wide open. The reducing valve only limits its output pressure, it does not control it.
41 Click on the variable orifice arrows to change the orifice area.
42 The pressure drop across the orifice will vary as it's size is adjusted. It increases as the orifice becomes smaller.
43 The supply pressure will equal the load pressure plus the pressure drop across the orifice.
44 When the supply pressure gets too high the relief valve will open and the motor speed reduce.
45 Observe how the output motor speed can vary with supply pressure because this also changes the pressure dropped across the orifice.
46 The small red marker on the load resistance slider indicates the motor speed.
51 A pressure compensated flow control valve provides a constant flow whatever pressure drop is available.
52 Adjusting the supply pressure does not affect the motor output speed, provided it is high enough to overcome the load resistance.
53 Also, observe how changing the output resistance does not alter the motor speed, provided the supply pressure is high enough to overcome the load resistance.
61 A pressure compensated pump maintains a constant pressure by varying the flow that it supplies.
62 When the maximum pressure setting is reached the pump flow starts to reduce because the setting will be lower than the relief valve setting.
63 Click on the solenoid button with the closed centre spool and you will see the pump reduces to almost zero.
64 Click the left-hand sequence arrow to switch between variable and fixed displacement pumps.
65 Because no flow is wasted with a variable displacement pump the input power requirement is greatly reduced.
66 Repeat the previous tests and compare the input power requirements against those for the fixed displacement pump.
71 Use the sequence arrow keys to experiment with different circuit designs.