Air Compressors (Part I)
Aftercoolers are used with air compressors to ______. a) reduce the temperature of compressed air b) decrease the density of compressed air c) dampen pressure pulses in the discharge air d) ensure complete expansion of the compressed air
a
Air compressors are equipped with unloading systems for the purpose of ______. a) removing all but the frictional load during starting b) relieving intercoolers of high temperature buildups c) providing high starting torque in the drive motor d) seating valve plates during compressor shutdown
a
An air compressor is equipped with an intercooler to ______. I. increase the efficiency of the compressor II. reduce the low pressure cylinder designed operating temperature a) I only b) II only c) Both I and II d) Neither I nor II
a
The device shown in the illustration is commonly used to ______? See illustration GS-0120. a) compress air b) pump heavy liquids c) pump refrigerant d) generate electricity
a
The device shown in the illustration is used to ______. See illustration GS-0029. a) unload the cylinders of an air compressor b) reduce the pressure in the ship's service air system c) grind sewage prior to entering the sewage treatment plant d) maintain correct tension on the drive belts while the compressor is in operation
a
The function of an unloader on a two-cylinder, two-stage medium pressure, air compressor is to ______. a) remove all but the friction load on the compressor motor when starting b) prevent water accumulation in air lines c) reduce motor starting voltage d) vary compressor speed
a
The function of the illustrated device is to ______. See illustration GS-0034. a) relieve compressed air from the intercooler after the compressor has cycled off b) relieve compressed air directly from the low pressure cyllinder after the compressor has cycled off c) provide variable discharge air flow to the compressed air system depending on the load on the system d) direct compressed air from the air receiver directly to the low pressure cyclinder unloading device
a
Air compressor cylinder unloaders 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
b
Air line lubricators are used in compressed air systems to lubricate ______. a) the suction and discharge valves b) tools and equipment served by compressed air c) air line reducing valves d) all of the above
b
An air compressor can be unloaded at start-up by ______. a) holding the discharge valve open b) relieving the intercooler pressure to the atmosphere c) using an enlarged, permanently opened clearance expansion space d) a precharged accumulator
b
For any given volume of compressed air produced by a multistage air compressor, interstage cooling will ______. a) increase the power required for compression b) decrease the power required for compression c) allow isothermal compression of the air charge d) allow the compressed air volume to remain constant
b
If all of the air charge has been lost from a ship service air receiver, the compressor mechanical unloading system will ______. a) fail to work, and the drive motor will trip the circuit breaker as the compressor will be overloaded b) fail to function as designed, but the compressor having no load will start with little or no difficulty c) still function normally at start-up d) Still function normally, but the safety interlock will stop the drive motor
b
If the intercooler of a low pressure air compressor becomes fouled either internally or externally, the ______. a) total capacity will be reduced b) volumetric efficiency will be decreased c) discharge pressure will decrease d) normal running time will be decreased
b
One function of the air receiver in a compressed air system is to ______. a) dry the air discharged from the intercooler b) minimize the system's line pulsations c) receive exhaust air from pneumatic accessories d) remove all traces of oil from the air
b
One of the functions of the component labeled "E" shown in the illustration is to ______. See illustration GS-0119. a) act as a hydraulic accumulator b) separate oil from the compressed air supply c) act as a oily water separator d) provide for expansion of refrigeration gases
b
Over pressurization of an air compressor intercooler is prevented by the ______. a) aftercooler relief valve b) intercooler relief valve c) last-stage unloader d) first-stage unloader
b
The function of the springs used with channel or plate-type valves for reciprocating air compressors is to ______. a) open the valves during downward strokes b) provide positive closing of the valves c) reduce compressor discharge pulsations d) reduce air intake and exhaust pulsations
b
When air compressors are arranged for automatic operation, the cylinders can be unloaded during starting by ______. a) bypassing the discharge valves b) fitting depressors which hold the suction valve plates open c) applying reduced voltage to the motor d) all of the above
b
When the compressed air reservoir is placed in line with an air compressor and is used as an aftercooler, the reservoir must be ______. a) fitted with a manhole b) frequently drained of condensed water c) fitted with a moisture trap at the inlet d) fitted with a sight glass
b
An air compressor is equipped with an intercooler and an aftercooler to ______. a) inject water vapor into the compressed air b) prevent overheating of first stage valves c) increase compressor efficiency and economy d) reduce the compressed air charge density
c
Condensate must be drained from the intercooler and aftercoolers of an air compressor because ______. a) the cooling effect of the condensate reduces the compressor's efficiency b) a danger of explosion exists whenever water is present in a compressor c) water contamination causes erratic operation of pneumatic components d) the volumetric capacity of the first stage is reduced if water remains
c
Condensate must be drained periodically from the air compressor receivers to prevent ______. a) second stage cylinder lockup b) oil sump contamination c) faulty operation of pneumatic valves d) corrosion of air receiver baffles
c
Separators are installed ahead of air line lubricators for the primary purpose of removing ______. a) the heat of compression b) air supply pressure pulses c) moisture in the air supply d) turbulence in the air supply
c
The air charge leaving an intercooler, or aftercooler of an air compressor can be expected to be ______. a) superheated b) supercooled c) at or below the dew point d) all of the above
c
The cylinders and intercoolers of most low pressure air compressors are cooled by ______. a) water b) oil c) air d) CO2
c
The device shown in the illustration is commonly referred to as a ______. See illustration GS-0119. a) hydraulic steering gear pump b) multistage ballast pump c) rotary lobe type air compressor d) control air dehydrator
c
The primary function of the device illustrated is to ______. See illustration GS-0029. a) intensify the pressure developed by an air compressor during its normal running operation b) open the discharge valves during the compressors operation to supply compressed air c) remove all but the frictional load of an air compressor at start up d) precharge the cylinders of an air compressor prior to the start-up of the unit
c
The purpose of an air compressor unloading device is to ______. a) drain water from the air receiver b) drain water from the cylinders c) delay the compression process until the motor is up to speed d) check pump alignment
c
The running unloader of the device shown in the illustration operates by ______. See illustration GS-0119. a) temporarily discharging the compressed air to the atmosphere b) holding open the high pressure stage reed-type suction valves c) throttling a butterfly valve located in the compressor suction line d) the use of an intercooler relief device
c
The unloading of an air compressor may be provided by ______. I. holding the intake valve off of its seat II. temporarily relieving the the intercooler to the atmosphere a) I only b) II only c) Both I and II d) Neither I nor II
c
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 compresser opposed only by friction d) reduce the compressor frictional load when starting
c
The usual method of unloading a low pressure air compressor at start-up is accomplished by ______. a) holding the discharge valve open b) the use of a precharged accumulator c) holding the suction valve open d) temporarily discharging to the air receiver
c
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
c
Which of the listed valve types is typically used for suction and discharge valves on modern low pressure air compressors? a) Poppet b) Rotary c) Reed d) Sliding
c
Air compressor receivers should be 'blown down' at least ______. a) yearly b) quarterly c) monthly d) daily
d
An important point of consideration when replacing a dry type intake filter on an air compressor is to ______. a) use the same wetting oil on the element as is used in the compressor lubrication system b) install a smaller size filter to allow for expansion of the element c) install only a filter consisting of a treated paper element d) select the proper size filter so that air flow is not restricted
d
An unloader is installed on an air compressor to ______. a) bypass the high pressure stage to the intercooler b) prevent excessive interstage pressure buildup c) control compressor discharge pressure d) remove the compression load as the compressor comes up to speed during starting
d
An unloader 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 service b) prevent excessive interstage pressure buildup c) control compressor discharge pressure d) remove all but the frictional load during starting
d
In addition to a pressure gage and a relief valve, an air receiver should be fitted with a ______. a) sight glass and manhole b) thermometer and sight glass c) thermometer and manhole d) drain connection
d
Intercooling of a multistage air compressor provides the advantages of reducing the work of compression on the succeeding stages, and ______. a) condensing part of the original water vapor content b) reducing the maximum piston loads c) increasing the volumetric efficiency d) all of the above
d
Moisture and impurities can be removed from pneumatic systems by using ______. a) air intake heaters b) desiccated suction strainers c) multi-orificed suction valves d) blowdown valves and filters
d
The heat of compression is partially removed from compressed air by ______. a) intercoolers b) aftercoolers c) compressor water jackets d) all of the above
d
Unloading of a low pressure, reciprocating, air compressor at start-up can be accomplished by ______. a) holding the L.P. discharge valve open b) the use of a precharged accumulator c) using a permanently enlarged clearance expansion volume d) temporarily discharging back to the compressor intake
d
When air compressors are arranged for automatic operation, the cylinders can be unloaded during starting by ______. a) bypassing the discharge to suction b) fitting depressors which hold the suction valve plates on their seats c) step unloading the cylinders in a multi-cylinder machine d) all of the above
d
Which of the following describes the function of the air receiver in the compressed air system on a MODU? a) Condenses moisture. b) Provides overpressure protection. c) Purifies the air. d) Acts as an accumulator.
d
Which of the following frequent maintenance procedures is required of compressed air receivers? a) A close watch on the temperature. b) Constant cleaning to remove oil and dirt. c) Constant testing of the relief valves. d) Frequent draining of water.
d
Which of the following statements describes the function of an air compressor intake filter? a) Protects against suction valve float. b) Provides a positive pressure on the air inlet valves. c) Prevents lubricating oil contamination of the compressed air supply. d) Protects against the damaging effects of airborne solid particles.
d
Which of the following statements is true concerning V-belt drives for reciprocating air compressors? a) Belts generally stretch slightly during the first few months of use. b) Excessively tight belts will overload the bearings. c) Belts are generally replaced as a set. d) All of the above.
d
Which of the following statements regarding low pressure, reciprocating, air compressor valves is correct? a) A relatively large cylinder clearance space is required for valve operation. b) Mechanical operating valve gear is required to open and close the valves. c) Only the suction valve requires a push rod and rocker arm mechanism for valve operation. d) Due to the physical construction of the valves, a relatively small cylinder clearance space is required for operation.
d
