# Circuit simulation experiment

## Experiment with a virtual hydraulic test rig

### Hydraulic circuit simulation

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### Fixed Pump Experiment

1. Select Supply>1 Fixed pump experiment, from the drop-down lists

♦ Click on and drag the green pressure gauge and place it over each pipe.

♦ Observe how the pressure changes around the circuit and think about what is causing this.

♦ Leave the gauge over the line before the directional valve and right-click on the directional valve to open the setup menu.

♦ Change the nominal size from 6 to 16mm. Observe what happens to the local pressure.

♦ Operate the cylinder extend solenoid.

♦ Observe what happens to the line pressure as the cylinder is moving and when it reaches the end of its stroke.

♦ Right-click on the cylinder rod to change the loads then operate the solenoid valve to see how the line pressures have changed.

♦ Check the pressure you see against hand calculations.

Experiment 1: It's normal for flow through the pipes to create small, local pressures.

Question 1: Why might the reservoir pressure be set above zero bar?

Reservoirs often have return line filters and/or coolers in the pipework and these will create small backpressures.

Experiment 2: Flow through an orifice will create a pressure drop across the orifice.

Question 2: If you increase the nominal size of the valve will the pressure drop increase or fall?

The larger the orifice the lower the pressure drop.

Experiment 3: Open center circuits stay at low pressure when not being used.

Question 3: What are the benefits of open center circuits?

Low standby energy losses. Efficient operation.

### Fixed Pump Open Center Valves Experiment

1. Select Supply>2 Fixed pump open center valves, from the drop-down lists.

♦ Click on the solenoids to operate the valves independently to observe how the cylinders move.

♦ Operate the two valves at the same time to explore how the movement of one cylinder affects the speed of movement of the other.

♦ Connect the supply node directly to the P port of each valve and observe what happens when each solenoid is operated. Or select the closed center circuit 3 and change the valves to open center.

Experiment 4: With two open center valves the return from one valve is fed into the supply of the second valve.

Question 4: What happens if both cylinders are operated together and one cylinder has reached the end of its stroke?

When either cylinder reaches the end of its stroke the other cylinder will stop moving.

### Fixed Pump Closed Center Valves Experiment

1. Select Supply>3 Fixed pump closed center valves, from the drop-down lists.

♦ Click on and drag the green pressure gauge and place it over each pipe.

♦ Observe how the pressure changes around the circuit and think about what is causing this.

♦ Operate the two valves independently to observe how the cylinders move.

♦ Operate the two valves at the same time to observe how the cylinders move.

♦ Observe what happens to the line pressure as one cylinder is moving and when it reaches the end of its stroke.

♦ Click on a cylinder rod and increase the friction force. Then operate the valves together to observe how the cylinders move.

Experiment 5: With two closed center valves the supply and return flows work independently of each other.

Question 5: What happens if both cylinders are operated together and one cylinder has reached the end of its stroke?

When either cylinder reaches the end of its stroke the other cylinder continues to move. Speeds may vary as there is only a certain volume of flow from the pump.

Experiment 6: With two closed center valves the cylinder speed will depend on the amount of flow they each take from the pump.

Question 6: What dictates how much flow each cylinder takes from the pump?

The cylinder with the smallest load (least pressure) will take the flow from the pump first.

### Fixed Pump With Accumulator Experiment

1. Select Supply>4 Fixed pump with accumulator, from the drop-down lists.

♦ Click on and drag the green pressure gauge and place it over each pipe until the accumulator is fully charged and the pump is switched to minimum pressure.

♦ Observe how the pressure changes around the circuit and think about what is causing this.

♦ Place the green pressure gauge over the accumulator to observe it's condition.

♦ Operate the valve to observe how the flow from the accumulator to the cylinder exceeds the maximum flow supplied by the pump.

♦ Experiment by changing the accumulator pre-charge pressure and relief valve setting to observe how this affects the stored volume of fluid in the accumulator.

Experiment 7: Accumulators store fluid under pressure so that it can be released into the system when required.

Question 7: What would happen if the pre-charge pressure was much lower than the working pressure?

The accumulator would not store enough energy to provide any usable volume.

Experiment 8: Accumulators are pre-charged with nitrogen to a given pressure, generally 90% of the system pressure.

Question 8: What would happen if the pre-charge pressure was above the maximum system pressure?

The accumulator would never receive any fluid from the circuit so would not store any usable volume.

### Variable Pump With Closed Center Valves Experiment

1. Select Supply>5 Variable pump closed center valves, from the drop-down lists.

♦ Click on and drag the green pressure gauge and place it over each of the two directional valves.

♦ Observe how the A and B line pressures are different in both valves and think about what is causing this.

♦ Operate the two valves independently to observe how the cylinders move.

♦ Operate the two valves at the same time to observe how the cylinders move.

♦ Compare the operation and performance of this circuit with that from the fixed displacement pump.

Experiment 9: A variable displacement pump only supplies the flow required by the circuit

Question 9: What happens if both cylinders are operated together and one cylinder has reached the end of its stroke?

When either cylinder reaches the end of its stroke the other cylinder continues to move. Speeds may vary as there is only a certain volume of flow from the pump.

Experiment 10: With two closed center valves the cylinder speed will depend on the amount of flow they each take from the pump.

Question 10: What dictates how much flow each cylinder takes from the pump?

The cylinder with the smallest load (least pressure) will take the flow from the pump first.

Experiment 11: Directional spools are supplied with a range of different center conditions.

Question 11: What is the main difference between the closed center and A+B to tank, versions shown?

The A+B to tank ensure the A and B lines only see tank pressure and the cylinder is free to move. Close center valves restrict movement of the cylinder but the A and B ports are likely to see half the supply pressure and the cylinder will probably creep.

### Diagnose 1 Fixed Pump Experiment

1. Select Supply>Diagnose 1 fixed pump, from the drop-down lists.

♦ Operate the directional valve. Click on the components to see their loads and settings.

♦ Diagnose what the issues with this system might be.

### Test Pump Performance

1. Select Supply>Test pump performance, from the drop-down lists.

♦ The orifice represents pump leakage, this increases if the pump is failing.

♦ Click and drag the small printer icon over the relief valve. Then press the large printer icon in the top menu bar

♦.Continue to change the pressure and click the large printer icon until you have sufficient test results to copy and plot in a spreadsheet graph.

♦ Right-click on the orifice to change its size. Then repeat the graph plot to compare the pump performance.