Ch.19 Compressors

If a belt-driven compressor with a 6″ pulley is being turned by a motor operating at 3600 RPM and equipped with a 3″ pulley, the compressor's shaft will be turning at _____.

1800 RPM

A ____ compressor compresses vapor between a matched set of helical rotors.

Screw

Which of the following methods is not used to modulate the capacity of a scroll compressor?

An unloader is used to hold the intake valve open so compression cannot take place.

All hermetic compressors require a crankshaft seal.

False

The volume between the top of the piston when it is at top dead center and cylinder plate is known as clearance space.

False

Which of the following explains why exhaust valves present more problems than intake valves?

Intake valves are continuously lubricated by cool refrigerant oil. Exhaust valves operate at a higher temperature than intake valves. Exhaust valve seats are more likely to collect carbon than intake valve seats

Which of the following statements regarding mufflers is false?

Mufflers are used only on hermetic compressors.

Which of the following types of valves has a valve stem that moves up and down in a valve guide?

Poppet Valves

Which of the following statements regarding poppet valves is false?

Poppet valves are closed by spring pressure.

Which of the following statements regarding piston rings is false?

The inner diameter of a piston ring is slightly larger than the piston diameter.

A crankcase heater prevents liquid refrigerant from being trapped with the oil in compressor crankcase.

True

A typical shaft seal is a two-part seal with half of it rotating with the shaft and the other half remaining stationary in the case.

True

The movement of blades in and out of their slots provides the pumping action for lubrication systems in some rotary compressors.

True

The purpose of the cylinder head is to support the valve plate and to seal the cylinder so compression can occur.

True

The types of unloader mechanisms and controls used on screw compressors can provide variable unloading.

True

Oil pumps are typically located _____.

at one end of the compressor shaft

Which type of compressor is most similar in construction to an automobile engine?

reciprocating

An overload relief valve must be built into an oil pump to protect the system against excessively high oil pressure.

true

On external drive compressors, the crankshaft seal rubbing surfaces should be lubricated.

true

Poppet valves are suitable only for low-speed compressors.

true

The pistons of some small hermetic compressors do not have piston rings.

true

A(n) ____ is used to temporarily reduce cylinder pressure during compressor start-up.

unloader

In reciprocating compressors, the intake and exhaust valves are located on the _____.

valve plate