152 STEAM BOILERS 



the necessity of straining the oil before admitting it to the 

 oil-burning system. The presence of sand and grit in the oil 

 supply vri.ll cause wear of the pump and erosion of'the burner 

 nozzles and orifices, and may result in the clogging of small 

 orifices. 



Oil Pressure. One of the requirements for the efficient 

 operation of an oil-burning plant is uniformity of the oil sup- 

 ply; for, if the oil supply is intermittent or varies in amount, 

 the combustion will be irregular and incomplete. To obtain 

 a uniform rate of feed it is customary to supply the oil at a 

 constant pressure by means of an ordinary duplex feed-pump. 

 The pressure at which the oil is delivered to the burners varies 

 in different plants and under different conditions. It may 

 range from 1 or 2 Ib. to 150 Ib. per sq. in., although the pressure 

 is usually between 10 and 40 Ib. per sq. in. The type of 

 burner employed will have some influence on the pressure 

 required; also, forcing of the boiler above its normal rating will 

 necessitate an increase in the oil pressure, to produce an 

 increased flow of oil. 



Objection to Gravity Feeding of Oil. When a standpipe is 

 used as a pressure regulator, the oil flows to the burners by 

 gravity. Some insurance companies refuse to insure plants 

 in which gravity feeding is practiced, on the ground that, if 

 a valve is left open, the boiler room may be flooded with oil, 

 thus greatly increasing the danger from fire. To overcome 

 the objection to having a considerable amount of oil held in 

 reserve above the level of the burners, a new form of apparatus 

 has been produced. This consists of a pump having a relief 

 valve between the suction and delivery sides. The relief 

 valve is set at the desired oil pressure, so that, if that pressure 

 is exceeded, the valve will lift and the excess of oil will be 

 returned to the suction side of the pump. When a standpipe 

 is used, it should be fitted with an automatic drain valve that 

 will open and drain out all the oil when the steam pressure falls 

 below the lowest pressure at which the oil can be atomized. 

 The flooding of the burners, with the attendant danger of 

 explosion, will thus be averted. 



Heating of Oil Fuel. The viscosity of certain crude oils 

 at ordinary atmospheric temperatures is very great, and it 



