Fig. 33 shows the installation of pumps and heaters at the City and County Hospital power plant, San Francisco.
When using air either at high or low pressure as a spray ing medium it is exceedingly desirable that the air be superheated before passing to the spraying tip, as thereby a considerable gain in efficiency can be anticipated.
Inasmuch as crude oils have been obtained from the earth they necessarily carry more or less sand or grit. The more viscous the oil the easier the sand and grit are held in suspension. In any installation of an oil burning plant special provision should be made for straining out all sand and foreign matter. Sand in oil not only clogs the burner openings but also wears out the small annular nozzles. Nearly all of the strainers inserted in oil burning systems are simple in construction and are often formed of a wire-gauze gasket set in the joints of the oil pipe. In order to take out the strainer for cleaning, however, it is necessary with such an installation to unbolt the joints of pipe and the more satisfactory arrangement is to use some strainer of the type shown in Fig. 34. Strainers of this type can be easily removed without tools or wrenches. The wire-gauze used in strainers should be made of wires of a width of mesh work equal to about one-half the width of the oil orifice in the burner. In the best practice a strainer is placed on each side of the oil pump, serving the two purposes of preventing sand from entering the pump and keeOng any particles of old packing or other material from the pump itself from going through the system into the burner.
Fig. 35 shows another type of strainer. By simply remov ing one cap screw the strainer can be withdrawn from the casing and thoroughly cleaned.
Any water entering an oil storage tank will settle to the bottom of the tank. When the oil is drawn from a fixed outlet at the tank bottom, this water will enter the system.
There is no practicable device that will directly separate the water from the oil. This separation can only be satisfactorily effected by allowing the water to settle to the bottom of the tanks by gravity. It therefore follows that if the suction to the oil pumps are placed in the bottom of the tanks, water will be often drawn when only oil is desired. A thread of water blown into the oil burner effectually extinguishes the flame in the furnace, and if oil does not soon follow the water, there may be difficulty in relighting without introducing an outside flame.
With most burners it is desirable that a uniform pressure should be maintained on the oil circuit to the burner. If it were possible to keep the pumps automatically and perfectly regulated, a uniform pressure could be secured. There are many devices on the market which set out to secure this uniformity of action. Oil-pressure regulators similar to those used as regula tors on steam mains have been tried, but in general have been found to be unsatisfactory, owing to the fact that the moving parts ,become clogged with sand or hydrocarbon. A so-called oil' pressuie regulator used as a single device is seldom satis factory. A reliable plan is to provide the oil chamber of the pump with what would correspond to an air chamber on the water pump, or to provide a separate tank or chamber in which a constant air pressure is maintained on top of the'oil by addi tional means. There are a number of designs of apparatus on the market which contain this feature of an oil 'air chamber, and corresponding regulating apparatus, which have given satis faction. Many of these installations contain automatic arrange ments whereby the change of level. of the oil in the chamber effects a control of the steam supply to the oil pump, and thus affords an automatic method of controlling the quantity of the oil supply to the burner system. In all oil installations it, is very important that the control of the oil pump and of the steam to the burner or of the compressed air, where air is used, should be so arranged that in case the delivery of any one of these fluids is reduced, or interrupted, a corresponding reduction or shutting off should be effected in the supply of the other elements. It is especially important that oil should in no case continue to be forced or pumped to the burners when the steam or air required for spraying is shut off, as in such event the unsprayed oil is liable to flood in upon the hot brickwork and a furnace explosion is sooner or later likely to occur. The underwriters' regulations in many cases specifically require that in the event of the stoppage of the oil flow to the burner all the other functions shall be caused automatically to cease. These are precautions dictated by considerations of ordinary safety, and various applications of valves and devices are in the market whereby these results can be attained.