单选题In a refrigeration system, foaming of the crankcase oil may cause the （）.Aexpansion valve to overfeedBcompressor to knockCwater regulating valve to failDcrankcase drains to plug
单选题
In a refrigeration system, foaming of the crankcase oil may cause the （）.
A
expansion valve to overfeed
B
compressor to knock
C
water regulating valve to fail
D
crankcase drains to plug
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Crankcase explosions in propulsion diesel engines result from ____.A.the splashing of lubrication oil by the crankshaftB.the dilution of crankcase oil with particles of combustionC.broken fuel lines spraying oil on the crankcaseD.the ignition of unburned fuel and air in the crankcase
If the refrigeration compressor crankcase is sweating, the cause may be due toA.a shortage of refrigerantB.the compressor running continuouslyC.liquid refrigerant returning to the compressorD.the compressor short cycling on the high pressure cutout
第二组Under normal operation, some lubrication oil mist may be discharged from the air compressor to the air start system. This oil may be from excess compressor cylinder lubrication, from faulty oil scraper rings, or may even be suspended oil vapor contaminating the engine room atmosphere and drawn in at the compressor suction. Oil discharge is kept to a minimum by draining the after cooler, air receiver and starting system. If small quantities of lubrication oil do get passed into the starting air system, they will deposit as thin moist film over internal pipe surfaces but are not readily combustible. If a cylinder non-return valve leak while the engine is in operation, some hot gas, possibly with unburned fuel and cylinder lubrication oil, may be blown through the valve to the adjacent air manifold. With further heating from the leaky valve, this, together with the already deposited oil film, will carbonize and form. incandescent carbon. If starting air is applied to the system while still hot, the high pressure air coming into contact with the burning carbon may cause an explosion. Such an explosion will cause a flame to pass back through the air start pipe system, evaporating the deposited oil film and igniting it in the presence of air. Very high velocities and shockwaves are generated which may rupture pipes and fittings.Alternatively, if excessive oil has entered the air start system, a mixture of air and oil droplets may be discharged through the open cylinder non-return valve during starting. This spray may ignite due to high temperatures in the cylinder, causing a flame through the still open valve to the air manifold.To prevent an explosion, air start valves must be correctly maintained and lubricated to ensure correct timing and free movement with positive closing. Oil in the system must be kept to a minimum, pipe lines must be drained and cleaned internally when necessary and oil discharge from air compressors must be kept to a minimum by good maintenance.The passage is mainly aboutA.crankcase explosionB.scavenge box fireC.starting air pipeD.the danger of explosion in the starting air system
Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur when the compressorA.has run continuously for a long periodB.suction pressure is below normalC.oil level is below normalD.starts after a long idle period
Sweating of the refrigeration system compressor crankcase is caused by_______ .A.too much superheatB.insufficient superheatC.suction pressure too lowD.excessive refrigerant returning to the compressor
______continuously extract the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity(不透明性) measuring track.A.The oil mist detectorsB.The smoke detectorsC.An oily water monitorD.Oil discharge monitoring and controlling system
Sludge may be formed in the oil in the crankcase of a reciprocating air conditioning compressor as a result of ______.A.refrigerant bubbles in the lube oilB.refrigerant reducing the lube oil viscosityC.oxidation(氧化) of the lube oil from overheatingD.reducing the floc or cloud point of the oil
单选题Before starting a diesel engine, you should always（）Acheck the pyrometer readingsBcheck the crankcase oil levelCcheck the fuel oil strainersDclean the fuel system
单选题The sudden reduction of pressure occurring within the crankcase of a refrigeration compressor during starting causes the （）.Asudden evaporation of wax crystals in the lubricantBsudden evaporation of entrapped air in the lubricantCrelease of refrigerant from the oil/refrigerant mixtureDrelease of dissolved lubricant from the refrigerant
单选题A refrigeration system compressor crankcase is sweating or unusually coldThis is an indication of（）.Aa shortage of refrigerant in the systemBair in the systemCan accumulation of liquid refrigerant in the crankcaseDa shortage of oil in the crankcase
单选题Refrigeration system compressor crankcase sweating is an indication of （）.Ainsufficient lube oil circulating through the systemBexcessive circulation of lube oil through the systemCinsufficient refrigerant in the systemDan overworked compressor
单选题If a refrigeration system compressor crankcase is sweating, you should （）.Aadd refrigerant to the systemBadjust the thermal expansion valve to the proper settingCadjust the float valve to the proper holding pressureDopen the hand expansion valve
单选题Large crosshead type engine generally has two lubrication systems, a function performed only by crankcase oil system is（）AlubricatingBcoolingCcleaningDneutralizing
单选题Excessive oil foaming in the crankcase of a refrigeration compressor can result in （）.Aoverheated compressor bearingsBexcess lube oil viscosityCcarbon deposits on the compressor piston ringsDwax crystals forming in the lubricant
单选题If the refrigeration compressor crankcase is sweating, the cause may be due to （）.Aa shortage of refrigerantBthe compressor running continuouslyCliquid refrigerant returning to the compressorDthe compressor short cycling on the high pressure cutout
单选题Foaming of the oil in a refrigeration compressor crankcase is caused by （）.Arefrigerant boiling out of solution from the lube oilBliquid refrigerant flooding the compressor and systemClube oil viscosity being reduced by refrigerant dilutionDcompressor suction pressure suddenly increasing
单选题An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.Aoil foaming in the compressorBhigher than normal suction and discharge pressures with a higher box temperatureChigher than normal discharge pressure with a normal box temperatureDthe compressor to run continuously
单选题Crankcase explosions in propulsion diesel result from（）Athe splashing of lubrication oil by the crankshaftBthe dilution of crankcase oil with particles of combustionCbroken fuel lines spraying oil on the crankcaseDthe ignition of unburned fuel and air in the crankcase
单选题Excessive oil foaming in the crankcase of a refrigeration compressor at start up can cause（）.Acompressor damage from improper lubricationBrefrigerant absorption by the lubricantCincreased viscosity in the lubricantDcarbon deposit on the compressor suction valves
单选题Crankcase sweating in a refrigeration system is caused by （）.Aa stuck solenoid valveBa shortage of refrigerantCtoo much oil in circulationDtoo much superheat
单选题The accumulation of air and other non-condensable gases in a refrigeration system will （）.Acause a loss of the liquid sealBcreate a vapor lock in the liquid receiverCcollect in the condenserDcause foaming of the oil in the crankcase
单选题In engines with system, the lubricating oil can be added to the engine through the filling hole in the crankcase cover, by using a hand oil can, or through the separator pipe（）Alubricating oilBdry sumpCcirculated tankDwet sump
单选题Sludge may form in the lubricating oil crankcase of a reciprocating air conditioning compressor as a result of （）.Awax precipitation in the lube oilBcontamination by dust, scale, or moistureCrefrigerant bubbles in the lube oilDrefrigerant reducing the lube oil viscosity
单选题The oil mist detectors continuously（） the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity measuring track.AdetractBextractCpump upDpump down
单选题Sweating of the refrigeration system compressor crankcase is caused by （）.Atoo much superheatBinsufficient superheatCsuction pressure too lowDexcessive refrigerant returning to the compressor
单选题Sludge may be formed in the oil in the crankcase of a reciprocating air conditioning compressor as a result of （）Arefrigerant bubbles in the lube oilBrefrigerant reducing the lube oil viscosityCoxidation of the lube oil from overheatingDreducing the floc or cloud point of the oil
单选题Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur（） when the compressor.Ahas continuously for a long periodBsuction pressure is below normalCoil level is below normalDstarts after a long idle period