An increase in rotor clearances in a rotary pump will （）.

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

An increase in the fuel injection pump discharge pressure can be caused by a/an _______.

A.leaking delivery valve

B.excessive bearing end play

C.plugged injector spray hole

D.increased plunger stroke

In a modern three-phase A.C. synchronous brushes generator, the excitation winding is on the rotor. That means .

A.The generator need not excitation.

B.The winding on the rotor is for inputting excitation current.

C.There are three phase windings on the rotor.

D.The generator has no brushes.

Which method should be used to warm up the pump turbines prior to discharge ________．

A.Lock the turbine rotor and slowly bleed in steam until operating temperature is reached

B.Run the pump at high speed with the discharge valves closed

C.Run the turbine at slow speed with the pump disconnected

D.Shut the discharge valve and run the pump at slow speed

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

An increase in rotor clearances in a rotary pump will ______.

A.increase discharge pressure

B.decrease pump capacity

C.decrease pump cavitation

D.decrease reaction ring clearance

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

Which pump must always be primed ________．

A.Centrifugal pump

B.Reciprocating pump

C.Rotary pump

D.All of the above