Question

Explain high pressure cutout with a neat sketch.

Hint:

It is a bellows and spring pressure switch on the discharge line that opens the motor circuit at excess pressure. Draw and label the parts.

Answer 1

Step 1: Understanding the Concept:
A high pressure cutout (HP cutout) is a safety switch of a refrigeration system. It protects the compressor, the condenser and the pipes from a dangerously high discharge pressure.

Step 2: Why it is needed.
The discharge pressure can rise because of a choked or dirty condenser, failure of the condenser fan or cooling water, a closed discharge valve or too much refrigerant.
A very high pressure can burst a pipe or damage the compressor.

Step 3: Construction.
The switch has a bellows (or a diaphragm) joined by a small tube to the discharge line of the compressor.
The bellows pushes against a spring. The spring tension is set by an adjusting screw to the cutout pressure.
A lever links the bellows to the electrical contacts, which are in series with the compressor motor circuit.

Step 4: Working.
Under normal pressure, the spring keeps the contacts closed and the compressor runs.
If the discharge pressure rises above the set value, the bellows expands and overcomes the spring force. The lever opens the contacts.
The motor circuit breaks and the compressor stops.
Most HP cutouts have a manual reset. The fault must be found and cleared before the switch is reset.

Step 5: Sketch (what to draw).
Draw the compressor discharge line with a small tube leading to a bellows. Show the spring, the adjusting screw, the lever, the electrical contacts and the supply to the motor. Label each part.

Final Answer:
The HP cutout is a pressure-operated switch that stops the compressor when the discharge pressure goes above a safe limit.