Oil Pressure Pump Circuit for a Compressor

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Objectives:

• Analyze a motor control circuit.

• List the steps of operation in a control circuit.

• Connect this circuit in the laboratory.

LABORATORY EXERCISE

Name _____ Date __________

Materials Required

Three-phase power supply 2 motor starters Control transformer 2 electronic timers (Dayton model 6A855) and 11-pin tube sockets 2 pilot lights 2 double-acting push buttons In the circuit shown in Ill. 1, the oil pump must start for some time before the compressor is started. When the start button is pressed, the oil pump should continue to run for some time after the compressor stops operating.

Ill. 1 Compressor oil pump circuit.

List the Components

List the circuit components.

Describe the Components

Give a brief description of what function is performed by each component.

Circuit Operation

Describe the operation of the circuit in a step-by-step sequence.

Connecting the Circuit

1. Connect the circuit shown in Ill. 1.

2. After checking with the instructor, turn on the power and test the circuit for proper operation.

3. Turn off the power and disconnect the circuit. Return the components to their proper location.

QUIZ:

To answer the following questions, refer to the circuit shown in Ill. 1.

1. Assume that the start button is pressed and the oil pump starts operating. After a delay of 5 seconds, the COMP pilot light turns on, but the compressor motor does not start.

Which of the following could cause this condition?

a. TR2 timer is defective.

b. COMP starter coil is defective.

c. The compressor motor is defective.

d. All of the above.

2. Assume that the circuit's in operation. When the stop button is pressed, both the compressor and oil pump stop operating immediately. Which of the following could cause this condition?

a. CR relay is defective.

b. TR1 timer is defective.

c. OP starter is defective.

d. Timer TR2 is defective.

3. When the start button is pressed, the oil pump starts operating immediately. After a delay of 5 seconds, the oil pump motor turns off. An electrician finds that the control transformer fuse is blown. Which of the following could cause this condition?

a. TR1 coil is shorted.

b. OP coil is shorted.

c. TR2 coil is shorted.

d. COMP coil is shorted.

4. When the start button is pressed, the oil pump motor starts operating immediately. After a long time delay, it's determined that the compressor motor won't start. Which of the following could not cause this condition?

a. OP coil is defective.

b. TR2 coil is defective.

c. COMP coil is defective.

d. The compressor overload contact is open.

5. When the start button is pressed, the oil pump motor starts operating immediately.

When the start button is released, however, the oil pump motor turns off. The opera tor then presses the start button and holds it down for a period of 10 seconds. This time the oil pump motor starts operating immediately, but the compressor motor never starts.

When the start button is released, the oil pump motor again immediately turns off.

Which of the following could cause this condition?

a. CR coil is defective.

b. TR1 coil is defective.

c. TR2 coil is defective.

d. COMP coil is defective.

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