RADIAL

Which davit type may be operated by one man ________．

A.Quadrantal

B.Gravity

C.Sheath-screw

D.Radial

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

At the middle pressure and large air quantity,_________ is more suitable.

A.an axial flow fan

B.a radial flow blower

C.a centrifugal fan

D.an auxiliary blower

题干材料：Due to the large amount of heat picked up by the air in boiler and engine rooms, it would be impracticable to maintain ambient conditions within the comfort zone by air conditioning or any other means. The normal practice is to provide copious mechanical ventilation; in boiler rooms, the quantity is equated to the combustion requirements, while in a motor ship engine room the supply may be 25-50% in excess of the requirements of the engines.

The axial flow fan is particularly suited to handle these large air volumes at the moderate pressures required, while of course the “straight-through” flow feature places it at an advantage over the centrifugal fan.

The increasing adoption of automation, with the provision of a separate control room makes less significant the fact that comfort conditions cannot be maintained in the engine room all the time.

问题：Which of the following devices should be taken to maintain ambient conditions of the boiler and machinery space?

A.air compressor

B.air cooler

C.air-conditioning plant

D.mechanical ventilation plant

In a motor vessel, the air quantity which the engine room need is_______ of the requirements of the engines.A.less than 25-50%

B.more than 125-150%

C.more than 25-50%

D.less than 125-150%

According to this passage, which of the following statements is true?

A.In boiler and machinery spaces, there is the air conditioning

B.In the boiler rooms the requirement of air volume should meet 25-50% of combustion requirement

C.To maintain the comfort zone in the separate control room the air conditioning plant should be fitted

D.The comfort conditions can be maintained in the engine room all the time

At the middle pressure and large air quantity,_________ is more suitable.A.an axial flow fan

B.a radial flow blower

C.a centrifugal fan

D.an auxiliary blower

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