A non-return valve in the air delivery line near to the comp

According to this passage, if the cylinder non-return valve were not leaky

A.an explosion would not be caused

B.there still would be a danger of explosion

C.oil would not deposit in the air pipe

D.pipe lines would not have to be drained

To add refrigerant to the low side of an air conditioning system, the refrigerant should be introduced through the_______ .

A.suction service valve as a vapor

B.suction service valve as a liquid

C.discharge service valve as a vapor

D.charging valve as a liquid

On a weather map, a large letter “H” means ______.

A.a high pressure area with cool, dry air, and fair weather

B.a high pressure area with warm, moist air, and inclement weather

C.horse latitudes, with rough seas and strong winds

D.a heavy squall line near the “H”

_______is usually driven by the engine camshaft and supplies pilot air to the cylinder air start valve.

A.An air receiver

B.An operating valve

C.An automatic valve

D.An air distributor

If the engine does start on air, but combustion does not immediately begin, the cause may be _____.

A.failure of the fuel pumps

B.starting air pressure too low

C.stop valve in air line closed

D.the turning gear still engaged

第二组

Under normal operation, some lubrication oil mist may be discharged from the air compressor to the air start system. This oil may be from excess compressor cylinder lubrication, from faulty oil scraper rings, or may even be suspended oil vapor contaminating the engine room atmosphere and drawn in at the compressor suction. Oil discharge is kept to a minimum by draining the after cooler, air receiver and starting system. If small quantities of lubrication oil do get passed into the starting air system, they will deposit as thin moist film over internal pipe surfaces but are not readily combustible. If a cylinder non-return valve leak while the engine is in operation, some hot gas, possibly with unburned fuel and cylinder lubrication oil, may be blown through the valve to the adjacent air manifold. With further heating from the leaky valve, this, together with the already deposited oil film, will carbonize and form. incandescent carbon. If starting air is applied to the system while still hot, the high pressure air coming into contact with the burning carbon may cause an explosion. Such an explosion will cause a flame to pass back through the air start pipe system, evaporating the deposited oil film and igniting it in the presence of air. Very high velocities and shockwaves are generated which may rupture pipes and fittings.

Alternatively, if excessive oil has entered the air start system, a mixture of air and oil droplets may be discharged through the open cylinder non-return valve during starting. This spray may ignite due to high temperatures in the cylinder, causing a flame through the still open valve to the air manifold.

To prevent an explosion, air start valves must be correctly maintained and lubricated to ensure correct timing and free movement with positive closing. Oil in the system must be kept to a minimum, pipe lines must be drained and cleaned internally when necessary and oil discharge from air compressors must be kept to a minimum by good maintenance.

The passage is mainly about

A.crankcase explosion

B.scavenge box fire

C.starting air pipe

D.the danger of explosion in the starting air system