Compressor Operations and Maintenance Flashcards
7 cards from real CARO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Compressor Operations and Maintenance flashcards as text
An operator notices frost forming on the suction line all the way back to the compressor crankcase of an ammonia reciprocating unit. What is the most likely concern?
Answer: Liquid floodback risking slugging of the compressor
Frost at the crankcase indicates very low or zero superheat, meaning liquid refrigerant may be returning and can slug the compressor.
What is the primary purpose of a crankcase heater on a reciprocating compressor?
Answer: To keep the oil warm and limit refrigerant migration into the crankcase during the off cycle
Crankcase heaters keep oil warmer than the coldest point in the system so refrigerant does not condense and dilute the oil while the compressor is off.
During startup of a reciprocating compressor after a long shutdown, the oil in the sight glass begins to foam heavily. What is the most likely cause?
Answer: Refrigerant dissolved in the oil boiling off as crankcase pressure drops
Refrigerant that migrated into the oil flashes off when suction pressure drops at startup, causing foaming and possible oil loss.
On a reciprocating compressor, what does a 'net oil pressure' reading represent?
Answer: Oil pump discharge pressure minus crankcase (suction) pressure
Net oil pressure is pump discharge pressure minus crankcase pressure, the true pressure available to lubricate bearings.
Which condition most directly increases the compression ratio of a refrigeration compressor?
Answer: Lowering suction pressure while condensing pressure stays the same
Compression ratio is absolute discharge pressure divided by absolute suction pressure, so lowering suction pressure raises the ratio.
Why must compression ratios be calculated using absolute pressures (psia) rather than gauge pressures (psig)?
Answer: Using gauge pressure can produce a false ratio, especially when suction is near or below atmospheric pressure
Gauge pressure excludes atmospheric pressure, so ratios at low suction pressures would be grossly wrong or undefined without converting to absolute.
An operator hears a sharp knocking sound from a reciprocating compressor that worsens when the suction line ices up. What should be done first?
Answer: Throttle or close the suction stop valve and reduce feed to the evaporator to stop liquid carryover
Knocking with frosted suction indicates liquid slugging, so the operator should throttle suction and correct the liquid feed to protect the compressor.