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单选题
The gear, screw, and vane pumps are all classified as （）.
A
variable stroke pumps
B
multistage pumps
C
positive displacement pumps
D
triple-ported pumps
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Which statement is NOT true?A.While displacement pump works, volume of the working chamber will increase and decrease alternatelyB.A gear pump always has two gearsC.Any vane pump will have a rotor within a ringD.A balanced vane pump has two outlet ports and they are positioned symmetrically
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Gear pumps are widely used to transfer any one of the following but .A.fuel oilB.lube oilC.hydraulic oilD.fresh water
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第二组Displacement pumps are those where the volume of the pump chamber is alternately increased to draw the liquid in from the suction pipe and then decreased to force the liquid out into the delivery pipe. Centrifugal pumps are those wherein an impeller rotating at high speed throws the liquid by centrifugal force from the center to the periphery of the impeller where the liquid is discharged through the delivery outlet.Gear pump consists of two or more meshing gears (spur, single or double helical teeth) enclosed m a close-fitted housing. These are used extensively for pumping fuel oil, lubricating oil and hydraulic oil. When gears are unmeshed on the inlet side, a pressure drop occurs that helps the atmospheric pressure acting on the surface of the oil in the reservoir to force it up the pipe to fill the void, the oil is then transferred around the periphery of the pump housing. As the gear teeth mesh again on the outlet side, they form. a seal that prevents oil from backing up to the inlet, the oil in the void is then be forced out into the discharge line.All vane pumps have a rotor driven within a ring (cam ring) by a drive shaft coupled to a prime mover. A cylindrical rotor with sliding vanes, generally in radial slots, rotates within the ring. The center of the rotor is offset from the center of the ring. In a simple vane pump, as the rotor turns, the vanes are forced outward against the inner surface of the cam ring by centrifugal force. This outward radial movement of the vanes and turning of the rotor causes the chamber between the vanes to increase as the vanes pass further away from the inlet port. This increase in volume results in a lowering of pressure until the atmospheric pressure is sufficient to force oil from the reservoir into the inlet chamber. Oil from the inlet is swept away by the vanes toward the outlet port through a decreasing series of chambers until it is forced through the outlet port. A vane pump of balanced design has an elliptical cam ring so that two pumping chambers are formed. This pump is in hydraulically balance, since the two intake and two outlet ports are diametrically opposed to each other. Therefore the side loads exerted on the rotor cancel out, thereby increasing bearing lift and permitting high operating pressure.According to the last sentence of paragraph 1, from where the liquid is discharged through the delivery outlet?A.from the eye of the impellerB.from passage of impellerC.from the periphery of the impellerD.from the impeller
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（1）onlyB
（1）and（2）C
（2）and（3）D
（1），（2）and（3）
考题
单选题A gear pump belongs to （） according to its working principle.A
reciprocating pumpsB
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depending onB
in relative toC
regardless ofD
because of
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单选题（） connected to the moving tiller will bring the floating lever pivot and the lever into line at right angles to the screw shaft axis.A
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（1）and（2）B
（1），（2）and（3）C
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单选题Cooling water pumps driven by direct reversing diesel engines are usually of the straight impeller vane type pump with a concentric housing to（）A
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diffuserC
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a reciprocating pumpB
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考题
单选题Gear pumps are （） type because they discharge a near constant amount of liquid regardless of pressure.A
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non-positive displacementC
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考题
单选题Which of the following statements is/are true regarding hydraulic pumps in general? （）A
Variable volumes can be obtained with gear pumps only by variation of the pump drive speedB
A radial piston pump houses sliding pistons in a stationary cylinder block through which passes a rotating pintle or ported shaftC
The amount of fluid displaced per revolution of an axial piston rotary pump is dependent on the angle formed between the cylinder block and valve plateD
All of the above
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单选题With reference to rules governing steering gear, which one of the following rules is incorrect? （）A
It is required that all ships are provided with two independent steering gear systems that is one main and one auxiliaryB
The auxiliary gear could be power operated in passenger shipsC
The auxiliary gear must be of adequate strength and sufficient to steer a ship at navigable speedD
All moving parts of the steering gear must be guarded against any possible damage
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单选题All diesel engines are classified as（）.A
four cycleB
compression ignitionC
vacuum ignitionD
external combustion
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单选题One of the main differences between the various types of screw pumps is in the （）.A
stuffing box diameterB
direction of rotation of the screwsC
pitch of the screwsD
type of driving gears
考题
单选题The gear and screw pumps are classified as （）.A
variable stroke pumpsB
multistage pumpsC
positive displacement pumpsD
triple-ported pumps
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