have been used with success in which the back-pressure was less than atmospheric, and in the table of proportions which has been given such cases are considered.

Such a system can be constructed by connecting the dis

charge from the system to an air-pump which will remove the water of condensation and to a great extent the atmospheric pressure; the heating surface will act as a condenser for the engine, and in case it is insufficient for this purpose a jet or surface condenser, supplied with cold water may WATER be used to supplement it. Instead of an air-pump and condenser, a siphon condenser, Fig. 196, may be used. This latter instrument is regularly on the market, and consists of a chamber above a convergent tube which receives the exhaust steam and a jet of water. This condenser depends for its action upon the fact that

SUPPLY

a column of water 34 feet in height will balance and overcome the atmospheric pressure. For its successful use it must be set so that the top of the condenser is at least 34 feet higher than the end of the discharge-tube, the bottom of which is to be submerged.

In a system of exhaust heating by-pass connections to the condenser should be provided, so that the heating surface would not need to be used in warm weather.

Besides the general system which has been described, other systems of great merit have been devised and put on

the market with many special and patented features. Of these we may mention first the Willames system, which is shown in Fig. 197, with details of construction. It will be seen that the exhaust from the engine is received into a large upright stand-pipe with back-pressure valve at top, and that the steam is drawn from near the top, and after passing through the

FIG. 197.-WILLAMES SYSTEM OF EXHAUST-STEAM HEATING.

radiating system, is received into a large branch-tee, which is

supplied with injection-water and serves as a condenser. The suction-pipe of the air-pump is connected to the branch-tee and acts to remove the atmospheric pressure from the entire system. A by-pass for summer use is shown. Water is heated

in the closed hot-water tank by a portion of the return, and may be used for any purpose needed, as, for instance, feedwater for boilers, heating by hot-water circulation, etc.

Another system of this kind which, by increasing the efficiency of surface, has met with much favor is that invented. by Andrew G. Paul. This differs in construction and principle of operation from that described, in that instead of using an airpump which receives all the exhaust, a small tank is connected with an induction condenser called an exhauster, which is connected to all the drips and to the air-valves of the radiators. An automatic device stops the operation of the exhauster as soon as the air is removed. The advantages of this system depend principally upon the quick removal of air from the various radiators and pipes, which constitutes the principal obstruction to circulation; the inductive action in many cases is sufficient to cause the system to operate at a pressure slightly below the atmosphere. Fig. 198 is a diagram* showing an application

FIG. 198.-PAUL SYSTEM.

of the Paul system to the exhaust-piping of a steam-engine. The connections of two radiators are shown, one of which is of the single-pipe, the other of the two-pipe, system. The exhauster, shown in the lower left-hand corner, receives all the

*Heating and Ventilation, November 15, 1894.

drips from the piping and radiators, and is connected with the air-valve of each radiator.

134. Combined High- and Low-pressure Heating-sysIn nearly all systems of heating with exhaust steam it is

tems.

necessary to arrange the piping so that at times live steam may be admitted in any amount required, as substantially described in Article 130.

In some instances high-pressure steam is carried in the boiler and may possibly be used in a few radiators, while the principal part of the building is heated with low-pressure steam

which is drawn directly from the boiler, and is reduced in pressure by passing through a reducing-valve. In this case the return-water of condensation passes to a tank or chamber at the lowest portion of the system, and is fed into the boiler by means of a return-trap or steam-pump. The principal elements of such a system is shown in Fig. 199, as designed by the Albany Steam Trap Company, and forms a useful illustration of the method of piping essential. To start the pump automatically and to keep it moving at the proper speed a pump-governor (Article 135) is used.

135. Pump-governors.—In non-gravity systems of heating the water of condensation is returned to the boiler by returntraps, as described in Article 99, page 167, or by steam-pumps. The trap is automatic, and when in good order will operate without attention, but the ordinary steam-pump needs to be started and stopped, as required, to remove the water. Το render the pump automatic a device termed a pump-governor is often employed. Many forms are used, but they consist in nearly every case of a tank containing a fleat or equivalent device, connecting with levers to the valve which admits

FIG. 200-PUMP-GOVERNOR WITH

OUTSIDE LEVERS.

steam for operating the pump. The tank is connected to the suction and located above the pump. When the tank is full of water, the steam-pump is put in operation by the rising of the float, which opens the steam-valve. When the tank is empty, the float falls, closing the steam-valve and thus stopping the pump.

A pump governor consisting of a float-trap with outside connections to a steam-valve, as described by F. Barron,* is shown in Fig. 200.

A steam-pump with attached governor is shown partly in section Fig. 201. In this case the float is of the bucket form, the valve for supplying steam to the pump is flat with a single

*Heating and Ventilation, March, 1894.