EXHAUST-STEAM HEATING Buildings having their own power and lighting plant should be heated by exhaust steam, about 90 per cent of the steam that passes through the en gines and pumps being available for this purpose.
A portion of this steam is used for heating the feed-water to the boilers. In a properly arranged system, very little fresh water need be supplied, since the condensation from the radiators, properly pu rified, is returned to the boilers.
To accomplish this purification, and to rid the steam of oil in order to prevent its coating the pipes and radiators, the steam is passed through a separator attached to the heater when all the steam is al lowed to enter it, or through an independent separator when only a portion of the steam passes through the feed-water heater. Only about one-sixth of the exhaust steam in w given plant is required to heat the feed-wai er that must be supplied to the boilers to take the place of the steam used in the engines, therefore all the exhaust need not enter the heater for the purpose of keeping up the proper tempera. ture of the feed-water.
A type of heater with a coke fitter is shown in Fig. 37; while Figs. 38 and 39 show two methods of making connections, the first when all the steam is allowed to pass through the heater, the latter when only a portion of the exhaust from the engines is allowed to enter.
A very essential appliance used with exhaust-steam heating is the valve, which makes good with live steam any de ficiency in exhaust that may occur. By adjusting the weight, any desired pressure, within limits, may be obtained.
A valve must be used with exhaust-steam heating, to regulate the pressure to be carried. It also acts as a safety-valve in case of over-pressure from any cause.
Heating systems are sometimes arranged by bringing to them live steam to be reduced in the building to any desired pressure by a reduc ing valve. In such cases there is no back-pressure valve; therefore a safety-valve should be placed on the main to act in case of trouble with the reducing valve and prevent too great a pressure on the radiators.
A by-pass should be used in connection with all pressure-reducing valves, to provide for overhauling them. A steam gauge connected not less than 6 feet from the valve on the low pressure side is a necessary attachment.
With exhaust-steam heating, an exhaust head should be placed at the top of the vertical exhaust main, to condense, as far as pos sible, the steam passing through it.
The drip pipe from the ex haust should be connected with the drip tank; or, if the exhaust has been passed through a first class separator, it may, if desired, be returned to the feed-water heater.
When a closed type feed water heater is used (see Fig. 40), a separate tank must be provided for the returns from the heating systems. High-pressure drips are trapped to this tank. In the case of the heater shown in Fig. 37, the live-steam returns are trapped to it. A common type of trap is shown in section in Fig. 41. In the position shown, the float or bucket hinged as shown, is held up by the buoyancy of the water, and keeps the valve at the upper end of the spindle in contact with the seat, preventing the escape of steam entering with the water through the inlet. The water, rising around the bucket, overflows it and overcomes its buoy ancy, causing it to fall and open the valve, the steam pressure on the water then forcing it out of the bucket until a point is reached where the buoyancy of the bucket again comes into play and closes the valve until the action is again repeated.
An extremely simple form of float trap is shown in Fig. 42, the hollow float raising the spindle and valve, permitting water to escape, but falling and thus closing the outlet when the water level reaches a point too low to cause the ball to float, thus preventing the escape of steam.
Special forms of traps known as return traps are used in small plants for returning to the boiler the condensation from the heating system.