Preventive Maintenance Flashcards

How is net oil pressure calculated for a compressor with a pressure-lubricated crankcase?

Answer: Oil pump discharge pressure minus crankcase pressure

Net oil pressure is the pump's actual lift above crankcase pressure.

After a compressor motor is replaced, what preventive step helps avoid premature coupling and bearing failure?

Answer: Checking shaft alignment with a dial indicator or laser tool

Correct alignment reduces vibration and wear on couplings, seals, and bearings.

A dirty evaporator coil with restricted airflow will most likely cause which condition?

Answer: Lower suction pressure and reduced capacity

Less airflow means less heat absorbed, which lowers evaporating pressure and capacity.

What is the purpose of bleed-off on an evaporative condenser?

Answer: To control dissolved solids buildup in the recirculating water

Bleed-off removes concentrated water to limit dissolved solids and scaling.

During a valve inspection, what should an operator verify on stop valves in an ammonia system?

Answer: That valve seal caps are in place and packing is not leaking

Seal caps and tight packing are the backup barriers against stem leaks.

A refrigerant or water pump makes a gravel-like noise and its discharge pressure fluctuates. What is the most likely cause?

Answer: Cavitation from insufficient net positive suction head

Cavitation happens when vapor bubbles form and collapse, causing noise, fluctuation, and impeller damage.

Which trend in an operator's log most strongly suggests a compressor problem needs attention?

Answer: A gradual, unexplained rise in discharge temperature at steady load

Rising discharge temperature can indicate worn valves, high superheat, or high compression ratio.