Low compressor head pressure in a refrigeration system can be caused by（）.

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  A . unload valve B . cooling water C . oil cup D . sum

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• A non-return valve in the air delivery line near to the compressor must be （）type similar to the compressor discharge valve.

  A、the low inertia B、the high inertia C、the low velocity D、the high velocity

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• Generally speaking, suction heads require to be （） for high speed or large capacities than for low speed or small capacities.

  A . greater B . smaller C . better D . worse

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• If the head pressure of a reciprocating refrigeration compressor is excessive, （）.

  A . the relief valve should open before the high pressure cutout B . the relief valve should open and allow the excess refrigerant to flow to the receiver C . the high pressure cutout switch should operate before the relief valve opens D . you should close in on the suction valve

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• 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 . Differential B . Trunk C . Barrel D . Valve-in-head

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• When a refrigeration compressor has developed a high head pressure as a result of a refrigerant overcharge, you should （）.

  A . increase the amount of cooling water to the condenser B . decrease the amount of cooling water to the condenser C . add more refrigerant to the system D . remove some refrigerant from the system

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• If a refrigeration compressor were short cycling on the low pressure cutout switch, the probable cause for this might be the （）.

  A . system was overcharged with refrigerant B . high pressure switch was improperly adjusted C . expansion valve strainers were fouled D . suction valves were leaking slightly

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• The device used for low-pressure control and high-pressure cutout on a compressor is called （）.

  A . cutout B . controller switch C . pressure controller D . cutout switch

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• A compressor should never be stopped （）.

  A、without first cooling it B、without first heating it C、without first unloading it D、without first loading it

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• On small, low pressure, air compressors, the cylinders are usually lubricated by the （）.

  A . splash method B . mechanical force feed lubricators C . detached sump method D . internal cooling passages in the crankshafts and connecting rod

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• 在音响调音专业中，英语单词Compressor表示“（）”。

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• If a refrigeration compressor is short cycling on high head pressure, you should （）.

  A . purge the condenser if the waterside is dirty B . check for proper water flow through the condenser C . increase the high pressure cutout setting D . reduce the cooling water flow

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• The major difference between the discharge and suction valves installed in most low pressure, reciprocating air compressors is that（）

  A、one valve seats upwards, while the other seats downwards B、the reed valves used on the discharge are made substantially thicker and heavier than thesuction valves C、the suction valve springs exert a greater tension than the discharge valve springs D、the discharge valve springs exert a greater tension than the suction valve springs

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• Before starting an air compressor, It should be （）.

  A . unloaded B . primed C . filled with water D . greased

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• Broken valve strips in an operating low pressure, air compressor will cause （）.

  A、an immediate crankcase explosion B、oil contamination in the compressed air C、a decrease in compressor capacity D、no immediate loss of the compressed air capacity

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• The unloading system on an air compressor will （）.

  A . increase compressor discharge pressure on demand B . increase compressor operating speed as necessary C . allow the motor to turn the compressor opposed only by friction D . reduce the compressor frictional load when starting

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• Air compressor cylinder un-loaders enable the compressor to （）.

  A . vary their speed according to temperature and load B . start and come up to speed before air compression begins C . change speed according to overload demands D . reduce compressed air charge density

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• A centrifugal compressor’s purge recovery unit（）

  A . reclaims water B . purges air without losing refrigerant C . purges air with some loss of refrigerant D . purges lube oil from the refrigerant

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• Badly leaking refrigeration compressor discharge valves will cause（）.

  A . overfeeding of the expansion valve B . damage to the condenser C . constant running of the compressor D . flooding of the receiver

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• If a refrigeration crankcase compressor were short cycling on the low pressure cutout switch, the cause might be that the （）.

  A . system was overcharged with refrigerant B . system was low on refrigerant C . suction valves were leaking slightly D . relief valve was leaking slightly

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  A.crawl B.retreat C.proceed D.drag

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• LOW ABOUT 300 MILES SOUTHWEAT OF LISBON 1004 MOVING SLWLY SOUTHEAST COMMA FILLING 1006 BY MIDNIGHT. This phrase is likely to be under the heading of ______.

  A.GALE WARNING B.24 HOURS FORECAST C.GENERAL SITUATION D.TROPICAL CYCLONE WARNING

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