单选题A （） pump is that where the volume of the pump chamber is alternately increased to draw the liquid in and then decreased to force the liquid out.A injectorB positive displacementC centrifugalD centripetal

Which statement is NOT true?

A.In a simple vane pump, the rotor and cam ring are exactly concentric

B.Balanced vane pump has an elliptical cam ring

C.Liquid in both gear pump and vane pump are forced out to the outlet.

D.Balanced vane pumps can work at a higher pressure than the simple vane pump

The amount of fuel delivered by a helical plunger fuel injection pump is controlled by ______.

A.varying the pump discharge pressure

B.varying the pump return pressure

C.rotation of the pump plunger

D.rotation of the pump barrel

Which statement is NOT true?

A.While displacement pump works, volume of the working chamber will increase and decrease alternately

B.A gear pump always has two gears

C.Any vane pump will have a rotor within a ring

D.A balanced vane pump has two outlet ports and they are positioned symmetrically

If it becomes necessary to pump bilges while a vessel is in port, which of the following procedures should be followed?

A.Pump only if the discharge is led to a shore tank or barge

B.Pump only during the hours of darkness

C.Pump only on the outgoing tide

D.Pump only as much as is necessary

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 impeller

B.from passage of impeller

C.from the periphery of the impeller

D.from the impeller