Valve overlap is the period during which （）.

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• A turbocharged, four-stroke/cycle diesel engine has a larger valve overlap than a naturally aspirated four-stroke/cycle diesel engine, in order to in crease the （）.

  A . temperature of the exhaust gases B . energy supplied to the turbocharger C . air pressure to the intake manifold D . purge of exhausted gases from the cylinder

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• During the valve overlap period, the exhaust pressure of a turbochargers, four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure （）

  A . effective cylinder scavenging and cooling B . constant pressure from the turbochargers C . cooler operation of the exhaust system D . effective constant pressure for turbocharger operatio

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• The（） is fitted in pair one is the main valve, the other the auxiliary or standby.

  A . main stem stop valve B . auxiliary steam stop valve C . feed check or control valve D . blow down valve

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• Now that the valve is not worth （）, I suggest it （）.

  A . to repair；to renew B . repairing；be renewed C . repairing；will be renewed D . to repair；to be renewed

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• What is the minimum recommended access point overlap for voice roaming？（）

  A . less than 10 percent B . 10 to 15 percent C . 15 to 20 percent D . 25 to 30 percent

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• In an engine with air inlet valve and exhaust valve on its cylinder heads the fresh air will enter into the cylinder （） and the gases exhaust （）, there being an adequate overlap between the inlet opening and the exhaust closing.

  A . downwards；upwards B . upwards；downwards C . downwards；downwards D . upwards；upward

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• Turbocharged four-stroke/cycle diesel engines utilize valve overlap for（）.

  A . improving cylinder scavenging B . preheating the combustion chamber C . reducing air charge density D . preventing valve wear

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• The emergency bilge suction valve is typically used （）.

  A . to inject cleaning additives when the bilges are extremely dirty B . when the main condenser becomes fouled, in order to provide additional cooling water circulation C . to connect the rose box to the independent bilge suction D . if the bilges become flooded and they can not be emptied by any other mea

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• A two-stroke diesel engine exhaust temperature will be lower than a four-stroke diesel engine of the same displacement because the （） (1) MEP is lower and the scavenging air is cooling the exhaust gases (2) valve overlap in a four-stroke

  A . (1) only is correct B . (2) only is correct C . both (1) and (2) are correct D . Neither (1) or (2) are correct

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• The diesel engine valve subjected to most severe conditions of service is the （）.

  A . cylinder exhaust valve B . air starting valve C . air inlet valve D . cylinder relief valve

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• The valve that prevents water from backing out of the boiler into the feed line is the（）.

  A . bottom-blow valve B . skin valve C . feed-check valve D . feed-stop valve

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• Which one of following statement is not true concerning the suitable sites of the direct acting relief valve and the pilot operated relieve valve?（）

  A . the direct acting relief valve is used for controlling lower flows and pressure B . the pilot operated relief valve is used for controlling higher flows and pressure C . the pilot operated relief valve is used for controlling lower flows and pressure D . the controlling accuracy of direct acting relief valve is worse than that of the pilot operated relief valve

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• The period of valve overlap is when （）.

  A . the inlet valve is open B . the exhaust valve is open C . both valves are close D . both valves are ope

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• If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.

  A . open；short；after B . closed；short；after C . open；long；before D . closed；long；before

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• The bulb for the thermal expansion valve is located（）

  A . in the middle of evaporator coils B . near the evaporator coil outlet C . near the evaporator coil inlet D . on the bottom row of evaporator coil

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• The function of the bypass valve on the self-contained breathing apparatus is to（）.

  A . control the pressure of the oxygen as it enters the body B . allow the wearer to manually give himself oxygen C . release excess heat which would otherwise cause the bottle to explode D . allow exhaled gases to pass outside the bottle

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• The emergency bilge suction or bilge injection valve is used to prevent （） of the ship.

  A . proceeding B . overloading C . collision D . flooding

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• To provide efficient roaming between the cells， which percent of cell overlap is recommended for2.4 GHz and 5 GHz access points？（）

  A . 5 to 10 percent for both 2.4 GHz and 5 GHz B . 10 percent for both 2.4 GHz and 5 GHz C . 20 percent for 2.4 GHz and 15 to 20 percent for 5 GHz D . 20 percent for 2.5 GHz and 10 percent for 5 GHz

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• The（） is a smaller valve fitted in the auxiliary steam supply line, and is usually of the non-return type.

  A . main stem stop valve B . auxiliary steam stop valve C . feed check or control valve D . blow down valve

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• On the all-purpose nozzle，the position of the valve when the handle is all the way forward is（）.

  A . shut B . fog C . solid stream D . spray

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• When a refrigeration compressor is in the ‘off’ cycle, the thermal expansion valve will（）.

  A . always be wide open when the compressor restarts B . continue to operate as if the system were in operation C . remain open until evaporator pressure equalizes, then close until the compressor restarts D . always be completely closed until the compressor restart

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• An interlock in the remote operating valve line stops the valve （） when the engine turning gear is engaged.

  A . to open B . opening C . open D . opened

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• When a refrigeration compressor is in the ‘off’ cycle, the thermal expansion valve will .

  A.always be wide open when the compressor restarts B.continue to operate as if the system were in operation C.remain open until evaporator pressure equalizes, then close until the compressor restarts D.always be completely closed until the compressor restarts

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• When the relief valve is used as a constant pressure valve, it is connected to the outlet of the hydraulic pump to ensure that the outlet pressure of the hydraulic system (pump) is constant.

  A:正确; B:错误

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