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单选题
To obtain maximum efficiency, two stage air compressors are usually （）.
A
horizontally mounted
B
never fitted with intake filters
C
fitted with intercoolers
D
operated in an unloaded condition at all times
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考题
Compressed air is supplied by air compressors to______.A.the air receiversB.the starting valvesC.the cylinder coversD.the distributors
考题
Diesel engines obtain combustion air through turbo chargers，blowers，or ______．A.Air startersB.CarburetorsC.Natural aspirationD.Air receivers
考题
单选题Hot gas defrosting uses the hot gas from （） to defrost the evaporator.A
starting air bottlesB
diesel enginesC
boilersD
refrigeration compressors
考题
单选题By far the greatest use is for diesel engine starting using air pressure of 25 bar or more provided by （）.A
rotary compressorsB
reciprocating compressorsC
centrifugal compressorsD
screw compressors
考题
单选题Condensate must be drained periodically from the air compressor receivers to prevent （）.A
second stage cylinder lockupB
oil sump contaminationC
faulty operation of pneumatic valvesD
corrosion of air receiver baffles
考题
单选题Condensate must be drained from the intercooler and after-coolers of an air compressor because （）.A
the cooling effect of the condensate reduces the compressors efficiencyB
a danger of explosion exists whenever water is present in a compressorC
water causes erratic operation of pneumatic componentsD
the volumetric capacity of the first stage is reduced if water remains
考题
单选题Tube leaks in the distillate cooler of a two stage flash evaporator will result in （）.A
loss of second stage vacuumB
contamination of the distillateC
lower feed inlet temperatureD
contamination of the second stage condenser
考题
单选题Intercoolers installed on starting air compressors, reduce the possibility of（）A
dust entering the high pressure stageB
lube oil carbonizationC
discharge pulsationsD
inter-stage vapor lock
考题
单选题In the operation of a flash type evaporator equipped with air ejectors,the air and non- condensable gases are evacuated directly from the （）.A
first stage flash chamberB
second stage flash chamberC
first stage after condenserD
second stage distilling condenser
考题
单选题Which of the following statements is true concerning the overall efficiency of air compressors?（）A
High pressure compressors are more efficient than low pressure compressorsB
Mechanical efficiency divided by compressor efficiency will equal the overall efficiency of the compressor unitC
Two stage compressors are generally more efficient than single stage compressorsD
The volumetric efficiency is decreased in multistage compressors
考题
单选题On small, low pressure, air compressors, the cylinders are usually lubricated by the （）.A
splash methodB
mechanical force feed lubricatorsC
detached sump methodD
internal cooling passages in the crankshafts and connecting rods
考题
单选题Increased air （） will raise scavenge efficiency and allow a greater mass of air to be compressed； more fuel may now be burned giving an increased power.A
specific volumeB
densityC
viscosityD
calorific value
考题
单选题Which of the listed operating conditions would have the greatest effect on the volumetric efficiency of an operating reciprocating air compressor?（）A
The density of the air entering the compressorB
The temperature of the air entering the compressorC
The designed rotating speed of the compressorD
A leaking head gasket
考题
单选题In reference to air conditioning, when air attains the maximum amount of moisture it can hold at a specific temperature, it is said to be （）.A
superheatedB
saturatedC
condensedD
convected
考题
单选题In order to distribute the side pressures over a wide area of the cylinder walls and liners, which of the listed types of pistons are used in modem low pressure air compressors?（）A
DifferentialB
TrunkC
BarrelD
Valve-in-head
考题
单选题An un-loader is installed on an air compressor to （）.A
bypass the high pressure stage to the low pressure stage on 100% of the air compressors in serviceB
prevent excessive inter-stage pressure buildupC
control compressor discharge pressureD
remove all but the frictional load during starting
考题
单选题Pump up the starting air reservoirs to their maximum pressure and （）the air reservoirs and air system.A
openB
closeC
drainD
vent
考题
单选题Bad valves operation of the reciprocating air compressors can be detected by observation of （）.A
the discharge temperature lowB
the discharge temperature highC
the discharge pressure riseD
the inter-stage pressure low
考题
单选题A vacuum is initially established in the first and second stages of a low pressure evaporator by the use of （）A
vacuum drag from the auxiliary condensate systemB
individual vacuum pumpsC
a single non-condensing air ejectorD
a two stage air ejector
考题
单选题Adequate attention must be given to the water cooling system of the air compressors, for （） can cause condensation on the cylinder walls.A
overcoolingB
poor coolingC
overloadingD
unloading
考题
单选题By far the greatest item of maintenance of the reciprocating air compressors concerns （）.A
the lubricationB
the coolingC
the moisture separationD
the valves
考题
单选题The efficiency of turbocharge system is increased by fitting a charge air cooler （） the compressor.A
insideB
beforeC
afterD
against
考题
单选题Explosions do occur （） caused by the ignition of oil or vapour gaining access from compressors or defective engine starting valves.A
in boiler drumsB
in refrigerating plantsC
in starting air pipesD
in air coolers
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