单选题The injector pump is operated by a cam which drives （） up and down.A the needle valveB the plungerC the pistonD the cylinder

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Older loop scavenged engines may have a single injector mounted centrally in the cylinder head. Because the exhaust valve is in the center of the cylinder head on modern uniflow scavenged engines the fuel valves (2 or 3) are arranged around the periphery of the head. The pressure at which the injector operates can be adjusted by adjusting the loading on the spring. The pressures at which the injectors operate vary depending on the engine, but can be as high as 540 bar. Some injectors have internal cooling passages in them extending into the nozzle through which cooling water is circulated. This is to prevent overheating and burning of the nozzle tip. Injectors on modern engines do not have internal cooling passages. They are cooled by a combination of the intensive bore cooling in the cylinder head being close to the valve pockets and by the fuel which is re-circulated through the injector when the follower is on the base of the cam or when the engine is stopped. As well as cooling the injector, re-circulating the fuel when the engine is stopped keeps the fuel at the correct viscosity for injection by preventing it from cooling down. Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder. Injectors should be changed in line with manufacturers&39; recommendations, overhauled and tested. Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed. The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomization and dribbling.

Modern uniflow scavenged engines have______.

A.a single injector mounted in the center of the cylinder head

B.several injectors mounted around the external boundary of the cylinder head

C.a single injector mounted at the external boundary of the cylinder head

D.several injectors mounted in the center of the cylinder head

A. up to 18 virtual libraries, 64 virtual drives, and 55000 virtual cartridges

B. up to 6 virtual libraries, 128 virtual drives, and 110000 virtual cartridges

C. up to 12 virtual libraries, 256 virtual drives, and 128000 virtual cartridges

D. up to 24 virtual libraries, 512 virtual drives, and 256000 virtual cartridges

Which of the following will be the advantage of a centrifugal pump as compared with a reciprocating pump? l.Its discharge is continuous; ll.It has no internal valves: lll.Upon accidental closing of discharge valve, excessive pressure will not build up()

A.l, ll

B.ll, lll

C.l ,ll.III

D.llonly

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

A spur gear pump should be operated with the discharge valves ______.

A.slightly opened

B.throttled

C.fully opened

D.halfway opened

Which of the following is operated from the main engine room console on an automated vessel?

A.Fire pump and lube oil pump

B.Lube oil pump and distilling plant

C.Distilling plant and shaft alley door

D.Shaft alley door and fixed CO2 release