US1928220A - Apparatus for heating by subatmospheric steam - Google Patents

Description

' Sept. 26, 19335 c. A. DURHAM PrARA'rus r03 HEATING BY suanuosramfic sum 4 Sheets-Sheet 3 Original Filed July 15. 19 27 Imfmfi [205/7512 A Julia 112 c. A. DUNHAM APPARATUS FOR- HEATING BY SUBATIOSPhERIC S TEAI Sept. 26, 1933.

Original Fi 1ed July 15, 1927 4 Sheets-Sheet 4 Im/enm [@7072 Azania Patented Sept. 26, 1933 PAT m OFFICE APPARATUS FOR HEATING BY QUE- ATMOSPHERIC STEAM Clayton A. Dunham, Glencoe, -lll., assignor to C. A. Dunham Company, Marshalltown, Iowa,

a corporation of Iowa Original application July 15, 1927, sci-m no.

205,978. Divided and this application February 25, 1929. Serial No. 342,557

. 9 Claims.

This invention relates to an improved apparatus for heating by sub-atmospheric steam, and more particularly to improvements in a multiple-unit vacumn heating system. Such a system is particularly adapted for use in very large buildings,

wherein different sections of the building are simultaneously subject to different temperature conditions, due to diiferent locations in the building, diiferent distances from thesource of steam 10 supply, difierent exposures, diiferences' in building construction, or other conditions, so that there are different heating requirements in these different building sections. This application is a division of mycopend'ing application Serial No. 205,978, filed July 15, 1927. In this parent application, the new method of heating by sub-atmospheric steam is claimed.

This system is an adaptation to the requirements noted hereinabove of the differential vacuum steam heating system disclosed and claimed in my Patent No. 1,644,114, granted October 4, 1927. Such a system includes a steam generator or other source of supply, from which steam is supplied to the radiators at an'adjustable subatmospheric pressure. A thermostatically operated trap at the outlet of each radiator normally prevents the escape of steam, but permits the escape of accumulated liquid condensate and air to a. return main leading down to an accumulator tank. Suitable'vacuum producing means serve to withdraw this liquid condensate and air, vent the air, return the water to the steam generator, and maintain the necessary vacuum in the return main and also throughout the system. By means of a' suitable reducing valve in the supply pipe, and suitable restricting orifices at the inlets of the radiators, the sub-atmospheric pressure of the steam delivered to the radiators may be varied, in accordance with the heat output de.- sired to meet the temperature requirements.- Dual control means is provided for the vacuumproducing mechanism whereby it is automatically operated to maintain a substantially constant dif-- ference in pressure between the supply and return sides of the system, regardless of the absolute pressure maintained in the supply main, and is also operated in accordance with the level or the accumulated liquid condensate in order to return this water to the steam generator.

According tothe present invention, in its preferred embodiment, each separate section of the building is provided with a diiiermtial vacuum heating system of the type just briefly described. A single generator or group of boilers is provided for supplying steam to the several separate distem might be advantageously used.

tributing systems, and the reducing valves for all oi. the systems are grouped or centralized adjacent suitable temperature indicating instruments connected with certain key-rooms in each of the sections or the building. These instru- 80 ments indicate the different simultaneous temperature requirements in the different building sections, and in accordance'with these indications the operator may suitably adjust the different reducing valves so that the subatmospheric pressure of the steam supplied to each unit or branch "of the system will correspond to the heating requirement in that building section. The returns from the several distributing systems are lead back to a group of separate vacuum-producing 70 mechanisms, all of which discharge their accumulated liquid condensates back to the common source of steam supply.

The principal object of this invention is to provide a new apparatus for heating large buildings, such as has'been briefly described'hereinabove and as is disclosed more in detail in the description which follows.

Another object is to provide means whereby an auxiliary pressure-controlled unit may be temporarily substituted for any one of the similar units normally used in the several distributing systems.

Another object is to provide means whereby an auxiliary vacuum-producing mechanism may be substituted for the similar mechanism normally 35 used in each of the systems.

Another object is to provide means whereby exhaust steam from an engine or other source may be distributed at the proper sub-atmospheric pressure to any one or all oi. the several distinct distributing systems.

Other objects and advantages of this invention will be more apparent from the following detailed description ofone approved for .n of apparatus suitable for carrying out the principles of this invention.

In the accompanying drawings:

Fig. 1 is a diagrammatic illustration of a large ofllce building wherein this improved heating sys- Fig. 2 illustrates the essential parts of any one distributing unit'of the heating system.

Fig. 3 is a plan view of the centralized supply and return portions of the heating system.

Fig. 4 is a vertical section through the boiler room and adjacent portions of the building, illustrating in elevation the mechanism shown in Fig. 3.

Fig. 5 is a detail elevation illustrating certain additions to and modifications of the structure shown in Figs. 3 and 4, whereby exhaust steam of the building.

Fig. 6 is an elevation, partly in section, through one of the radiator inlet valves and restricted inlet orifices.

Referring first to Fig. 1, which illustrates a large building of the new set-backconstruction, it will be noted that this building has been divided graphically by dotted lines into eight separate blocks or sections A, B, C, D, E, F, G'and H. The section Dis not visible, but its location will be obvious from the drawings. It will be apparent that a building of this size is subject in different locations to a widely diifering variety of temperature conditions. Certain portions of the building will be continuously shaded or protected by adjoining structures, whereas other portions will be constantly exposed to the sun or air currents. These conditions will vary at different sides of the building, and at different heights. As a general rule in this country, the heat requirements on the southern sides of buildings are not as great as on the northern exposures. The decreased cross-sectional area and proportionately increased outside exposure of the upper portions of the building will usually increase the heat loss and require increased radiation from the heating system. If the steam or other heating medium were supplied to all portions of the building at the same temperature, it will be apparent that ..this temperature would have to be sumcient to meet the heat requirement of the coldest section of the building, and would, therefore, be greatly in excess of the heat requirements in other portions of the building. According to this invention, the building is divided into a plurality of separate divisions or-sections, and the heating medium is supplied to the group of radiators in each section at a temperature suiiicient to meet the average heat requirement of. that section. The steam or other heating medium is supplied from a common source and the temperature of the steam delivered to each section of the building is controlled by the sub-atmospheric pressure of the steam supplied to this section. More specifically, the pressure of the steam taken from the common source is reduced when it is delivered to each separate distributing system so that the sub-atmospheric pressure of the steam supplied to that system will correspond to the steam temperature necessary to meet the average heating requirements in that section. In the example illustrated, the main lower section of the building has been divided into four corner blocks or divisions A, B, C and D. The next largest setback has been divided into two sections E and F. Presumptively one oi these would be a northern exposure and the other a southern exposure. The

two upper set-backs have been divided vertically into two sections G and H. The example shown is merely illustrative, and each building would be divided into more or less'sections, of varying size and location, according to the particular conditions presented by the location and construction Referring now to Fig; 2, I will briefly describe a single unit oi a differential vacuum steam heating system, such as is disclosed and claimed in my'Patent No. 1,644,114, hereinabove referred to. Steam from any suitable generator is supplied through the reducing valve K andsupply main L to the radiators M. Condensate and air are drawn out of the radiators through thermostatic traps N and through return main .0 to the accumulator tank P. The vacuum producing mechanism incumulated liquid condensate in the tank P.

Steam passes from the boiler or other source of supply through pipe 1 and cut-off or gate valves 2, to andthrough the reducing valve K into the supply main L. The reducing valve K may be of the well known form embodying balanced cutoff valves whose movements to closed or open positions are governed by the enclosed pressure diaphragm 3 and the balanced weights 4 and 5. The diaphragm 3 is subject on one side to the steam pressure in supply main L, by means of the pipe 6 connected at one end to the housing of the diaphragm and at the other end to the supply main at a point sufflciently remote from the valve K to be uninfiuenced by pressure disturbances in the vicinity of the valve. This reducing valve Kdiifers from similar valves heretofore in use, in the fact that the balancing weights 4 and 5 are so proportioned and positioned that a desired sub-atmospheric pressure may be maintained in the supply main L, while a higher pressure (either sub-atmospheric or super-atmospheric) exists in the supply pipe 1. By properly adjusting the weights 4 and 5 (or other equivalent spring or balancing devices which may be used), any desired degree of vacuum may be maintained in the supply pipe L. Preferably a pressure gauge 7- is provided to indicate this ,vacuum or subatmospheric pressure.

Instead of the manually adjusted reducing valve K, as shown in Fig. 2, an automatic temperature controlled valve might be substituted, as disclosed for example in my Patent No. 1,644,114, hereinabove referred to.

The risers 8 lead from the supply main L to furnish steam to the several radiators M, two of which are here shown by way of example, although it is to be understood that any desired number of radiators may be used. In a similar 1- manner the risers 9, here shown, lead to. radiators on a floor above those indicated in the drawings. Steam passes from the riser 8 through inlet valve 10 into the radiator This inlet valve will normally be open when the radiator is in service to permit free passage of steam from the supply main to the radiator, but the valve may be closed when any individual radiator is not to be used for heating purposes.

As indicated in Fig. 6, an orifice plate is interposed in the pipe leading from the valve 10 to the radiator, this plate restricting the flow of steam so that for average pressures in the supply piping, the maximum quantity of steam that the radiator will receive is fixed and proportioned to the condensing capacity of the radiator. The

orifices 111 in the plates 110 of the various radiradiator M is a thermostatically operated steam trap N, which normally retains the steam within the radiator, but permits the outflow of accumulated liquid condensate and air through pipe 11 to the return main 0. This thermostatic steam trap is preferably of the type emb dyin a valve which is moved toward or from its seat by the expansion or contraction of a fluid-filled thermostatic disc.

The liquid condensate and air flow downward by gravity, assisted by the suction of the vacuum producing mechanism R, hereinafter described, through the return main 0 and suction strainer 12 into the accumulator tank 1?. The water of condensation and air accumulating in the supply main L is vented through the pipe 13 and float and thermostatic trap 14, and pipe 15 to the return main 0, and is afterwards handled along with the condensates from the radiators. I

The suction producing mechanism R, as here shown, comprises a tank 16 partially filled with water, from the lower portion of which a pump 1'7 withdraws water through pipe 18 and forces this water upwardly through a Jet exhauster 19 back through pipe 20 into the upper portion of tank 16. This hurling water circuit produces a suction in the casing of ejector, 19, which draws up the water and air from the lower portion of the accumulator tank P, through pipe 21, these gases and condensates being carried along with .the water of the hurling circuit and discharged into the tank 16. A one-way check valve 22 in pipe 21 prevents the return of these materials to the accumulator tank. The gases discharged into tank 16 are vented to the atmosphere through pipe 23, provided with check valve 24. The pipe 23 is here shown as discharging into a sewer connection at 25. A second outlet from the centrifugal pump 17 leads through valve 26, pipe 2'7, check valve 29 and cut-ofl valve 28 back to the steam generator, or to a feed water heater, stain the installation hereinafter described. A float 30 in the tank 16 operates, when the level of accumulated liquid in the tank 16 has reached a certain height, through the link and lever connections 31 to open the valve 26 and permits the pump 1'1 to force water out through pipe 27 and check valve 29.

The motor 32 which drives the pump 17 is connected by. wires 33 with the starter 34, which is under the separate and independent, control of two distinct switch mechanisms as and as. Switch 35 is controlled through lever mechanism 37 by a float'38 positioned in the accumulator tank P. When a certain amount of liquid condensate has gravitated through return main 0 into this tank, the float 38 will be lifted sumciently to close the switch 35, which results in starting the motor 32 and the vacuum producing mechanism commences to function to withdraw the condensates and air in tank P and discharge them into tank 16. Here the gases are vented through pipe 23, and when suilicient water has accumulated, it is returned to the boiler or to the feed water heaterv in the manner already described. v

Switch 36 is controlled by the diflerential pressure regulator S, which comprises a movable diaphragm adapted in a well known manner to open or close the switch 36 through the lever connections 39. The diaphragm of differential pressure regulator S is subject on its opposite sides to the pressure existing in the supply and return mains, one side being connected through pipe 40 with the supply main L, and the other side through pipedl withthereturnmalno. Sincebothpipes 40 and 41' will become filled with liquid condensate, they are initially 'fllled with water and the vertical lengths of the two pipes must be of the same vertical height, as shown, in order to equalize the water head pressing on each side of the diaphragm of the pressure regulator. when the diflerence in pressure between the two mains falls below a certain minimum, switch 36 will be closed, whereupon the motor 32 will be started and the pumping mechanism will operate to suck liquids and air from the tank P and thence from the return main 0. This will lower the pressure in the return main 0 and the pump-will continue to operate until a desired maximum pressure differential is established between the return and supply mains, whereupon switch 36 will be opened to stop the motor 32.

In the normal operation of the system, as so far described, the reducing valve K is adjusted so as to maintain the desired degree of vacuum in the supply main L. Asis well known, steam will be generated at atmospheric pressure at 212 F. Under higher pressures steam will be generated at higher temperatures, and conversely under a vacuum, steam will be generated at lower temperatures, the temperature of the steam depending upon the degree .of vacuum existing in the system. This principle is utilized in this heating system sothat by varying the sub-atmospheric pressure in the supply main L, the temperature of the steam delivered to the radiators M is correspondingly varied so that steam at comparatively low temperatures may be maintained in the radiators when prevailing weather conditions necessitate only a mild radiation of heat from the radiators. Steam may be more economically generated at lower temperatures, and it is more emcient and economical to maintain a constant supply of steam at a comparatively low temperature than an intermittent supply of steam at a higher temperature.

, While the degree .of vacuum existing in the system may be varied from atmospheric pressure, or slightly above, to as low as perhaps 24 inches of vacuum, in order to obtain the desired heating effect from the radiators, it is also desirable that a substantially constant and relatively small difference in pressure be maintained between the supply and return sides of the radiators, this pressure differential being just sumcient to insure the proper circulation of steam and provide for withdrawing the condensates and air. Accordingly, the vacuum producing system is adjusted to operate to maintain this fixed pressure differential between the supply and return mains, but as hereinafter explained, in order to maintain this fixed differential, it will also function to maintain the desired degree of vacuum throughout the system.

When starting the operation of this system,

with steam in the pipe 1, the pumping mecha-.

nism R is put into operation to create a suction in the system. At this time the system will be empty of steam and the thermostatic traps N will be open. There will be no substantial difference in pressure between the return and sup-- traps until-such time as suiiicient condensate has 150 accumulated to open these valves and-permit its withdrawal. The pumping mechanism R. will continue to operate until the sub-atmospheric pressure in return main 0 (which is now out of: from the supply main L bythe closed traps N) has been lowered until the necessary pressure difierential has been attained, whereupon the control mechanism S will operate the switch 36 to stop the motor 32. As steam condenses in the radiators M, the pressure in the radiators and supply main L will be lowered below the subatmospheric pressure for which the valve K is set, and this valve will open and admit more steam to the supply main and radiators, thus keeping the radiators full of steam at the desired sub-atmospheric pressure. The thermostatic traps N will automatically open to permit the accumulated condensate and air to pass out into the return main 0, and will again be closed when steam attempts to pass through these traps. This entry of air and condensate into the return-main 0 will somewhat raise the pressure in this main so that the diiference in pressure between the return main and supply main may fall below the necessary minimum, whereupon the control device S will operate the switch 36 to start the motor 32, and the pumping mechanism R will begin functioning at once to again reduce the pressure in the return main 0. The pumping mechanism' R will only operate at such intervals'as is necessary to maintain the pressure difierential between the supply and return mains, or when the accumulation of liquid in the accumulator tank P necessitates its removal to tank 16 and thence to the generator.

The object sought to be attained by this systemis the substantially constant emission of heat from the radiators at a rate just suflicient to replace the heat lost from the building. This is accomplished, not by turning the radiators on or off at intervals, but by changing the temperature of the steam maintained in the radiators, and this in turn is accomplished by varying the sub-atmospheric pressure of this steam. This pressure variation is accomplished, in the system here disclosed, by adjustment of the reducing valve K.

Having thus briefly explained the operation of one unit of the improved differential vacuum heating system, I will now return to the explanation of the multiple-unit system which forms the particular subject matter of the present invention. In general, it may be stated that a system such as has just been briefly described is utilized to independently heat each of the sections A to H inclusive of the building, as shown in Fig.

1. Referring now to Figs. 3 and 4, at W is shown thesteam generating plant, consisting in this case of a group of boilers 42 to 47 inclusive. At X is shown the grouped or centralized control valves for the several branches of the system, and at Y is similarly grouped the pumping mechanism for the several units. At Z is indicated the e neers room or control room, wherein the operator may observe the temperature conditions in the various portions of the building.

The several boilers 42 to 47 inclusive each feeds through a pipe 48 and valve 49 into the high pressure header 50. Steam is fed from high pressure header 50 through reducing valves 51 and pipes 52 to the lower pressure headers 53 and 54. Steam is supplied through the several pipes 1 leading from headers 53 and 54 to the group of reducing valves K to K inclusive to the supply pipes L to U inclusive of the eight distinct branch heating systems which supply heat to the respective sections A to H or the building, as indicated in Fig. 1. At an adjacent location, the return pipes O to 0' of these respective branch heating systems lead back to the accumulator tanks P. to P', respectively. The condensate delivery pipes 27. of the several branch systems all feed into a common header pipe 55, leading through check valve 56 to the 'feed water heater indicated diagrammatically at 57. A pair of similar boiler teed pumps 58 and 59 connected in multiple so that either one or both may be used, serve to pump water from the feed water heater 5'7 through pipe 60 and header 61 back into the several boilers 42 to 47 inclusive. By means of the several valves 62 and feed pipes 63, the water may be fed selectively from header 61 into anydesired boiler or boilers.

Steam may flow from the low pressure header 53 through pipe 64 and the auxiliary reducing valve K (similar in all respects to any one of the reducing valves K to K), into the by-pass pipe 65 positioned transversely of the several supply pipes L1 to L8 inclusive. From the bypass pipe 65, branch pipes 66 lead through outofi valves 67 into the respective supply pipes L to L This reducing valve K and by-pass 65 serve as an emergency control valve which may be substituted for any one of the main reducing valves K to K", respectively. In a similar manner, branch return pipes 68 lead through cut-off valves 69 into the by-pass pipe 70 which feeds into an auxiliary accumulator tank P The auxiliary pumping unit R feeds back into the header 55 similarly to the main pumping units R to R inclusive. By suitably manipulating the cut- oil valves 28 and 69, the auxiliary pumping unit may be substituted for any one of the units R to R". In this way, anyone of the pumping units may be withdrawn from service when repairs are necessary, without incapacitating the corresponding branch heating system.

In a certain key-room '11 (see Fig. 1) in each of the sections A to H inclusive, which rooms are selected to give the average temperature conditions in each respective section, are located thermometers or thermostats which respectively actuate certain indicating instruments '72 in the instrument room Z. By means of these indicators 72} the engineer or operator can see at any time the temperature conditions existing in each of the several sections of the building and can regulate the reducing valves K accordingly to bring the temperatures to any desired normal. For example, let us suppose that it is desired to maintain a temperature of 70 F. throughout the building, but the engineer notes that the indicator 72 corresponding to the section G indicates that a'temperature lower than this, for example, 65", prevails in that section or the building. Assuming that the reducing valve K controls the branch heating system leading to section G, the

engineer will adjust this valve so as to increase the pressure (or decrease the vacuum) of the steam supplied to this branch heating system. This will increase the temperature of the steam delivered to this respective section of the building ,and will bring the temperature back to normal. On the other hand, let us suppose that one of the indicators shows that the temperature in building section F has become too high, for example F. Assuming that the reducing valve K controls this branch heating system, the engineer will adjust this valve so as to decrease the pressure (that is increase the vacuum) in the supply pipe 1. leading to this section oi the building. This will decrease the temperature oi the steam deliveredto this branch heating system, and the resulting decreased radiation irom the radiators in this section oi the building will bring the temperature back to normal. Ii desired, pressure indicators 73 may also be located in the instrument room Z showing the respective sub-atmospheric pressures existing in the several branch heating systems. Other pressure indicators will also be located either in the instrument room or adjacent the several pumping units to show that the proper pressure diiierential is being maintained betweenthe supply and return pipes of each branch system.

The distinct advantage-oi this system resides in the iact that steam oi various temperatures can be simultaneously furnished to diflerent parts oi the same building having diiierent exposures and different heat losses. The amount of heat waste is minimized throughthe prevention oi overheating an unexposed section in order to keep the exposed section iully heated. With this system it is possible to maintain the entire building at a substantially uniiorm temperature without continually turning on and of! the radiators in those portions oi the building where less heat is required. The centralized system oi control permits the entire system to be regulated by a single operator who is always cognizant oi the temperature conditions prevailing in any. part oi the building.

While in theexample here illustrated, we have shown a steam generatorcapable oi developing high pressure steam, this steam pressure being brought down by reducing valves beiore it is delivered to the low-pressure headers 53 and 54, it is not at all essential to the-operation oi this system that high pressure steam be developed.

The pressure in the boiler need notexceed the pressure required to heat the most exposed portion oi the building, and this boiler pressure may cities to have central steam supplied from an outside sourcefinstead oi by a boiler plant in the building. In such an installation the steam would be delivered to the low pressure headers 53 and 54 through suitable reducing valves in a similar manner to that already described. In such a system, that'portlon oi the apparatus which is utilized to deliver the condensate-back to the boiler could be eliminated.

In Fig. 5 is illustrated a modification whereby exhaust steam irom engines-or other high pressure apparatus may be utilized. A header '74 positioned parallel with the low pressure header.

54 is connected through branch pipes '15 in which are located reducing valves '76 and cut-oi! valves 77, with the several supply mains L. The exhaust steam header '74 may. take the] place oi the by-pass pipe 65, already described, or may be arranged in parallel therewith. The reducing valves'lcmaybesimilarinallrespectstotl ie the reducing valve in each oi' these pipes, each reducing valves K, already described, and by suitably adjusting these valves and the cut-oi! valve 7'7, the exhaust steam may be fed into any or all of the supply pipes L, either simult with or as a substitute for the steam supplied direct from the boilers through the reducing valves K. It will be noted that this exhaust steam is "delivered directly into the vacuum mains L, thus making possible a reducing oi the pressure in the exhaust pipes and adding materially to the power. oi the engines. v

I claim:

1. :In a steam heating system, a header receiving steam irom a source of supply, a plurality oi distributing systems each system including a supply pipe and a reducing valve through which the supply pipe communicates with the header, an auxiliary reducing valve communicating with the header, and a by-pass pipe leading irom the auxiliary valve and having valved branches leading respectively to the supply pipes oi all oi the systems.

2. Ina steam heating system, a header receiving steam irom a source oi supply, a plurality of distributing systems each system including a supply pipe and a reducing valve through which the supply pipe communicates with the header, a second source of steam supply, and independent connections irom this source to each oi the supply pipes at the low pressure side oi of these independent connections including a reducing valve.

3. In a steam distributing system, a source oi steam, a plurality oi distinct distributing systems each receiving steam at sub-atmospheric pressure from the source,each system comprising a means for regulating the sub-atmospheric pressure oi the steam supplied to the system in accordance with the heat output desired in that system, said regulating means comprising a vacuum-producing means ior maintaining the sub-atmospheric pressure in that system, and

a control means ior maintaining a pressure diiierential between the inlet and outlet sides oi the system suflicient to insure a flow oi steam through the system, an auxiliary vacuum pro-' ducing means, and a by-pass pipe having branches connecting thelast named means with" the outlet side oi each oi the systems.

4. In steam heating apparatus, a source oi steam, a plurality of distinct distributing systems each receiving steam irom the source, each system comprising a group of radiators, a supply pipe leading from the source and having 188a branches leading to each radiator, exhausting means ior withdrawing air and condensate irom the radiators without permitting the escape oi steam therefrom, and separate restricting means positioned in each supply pipe and in each branch thereoi for separately controlling the quantities oi steam delivered to each distributing system and to each radiator therein, the exhausting means and the restricting means in the supply pipes cooperating to separately maintain the steam in each separate group oi radiators at a distinct sub-atmospheric pressure which is determined by the setting oi the respective restricting means in each supply pipe.

5. In a steam heating apparatus, a steam generator, a plurality oi distinct distributing systems each receiving steam irom the generator, each system comprising radiating means, means ior separately regulating the sub-atmospheric pressure oi the steam supplied to the system in accordance with the heat output desired in the space heated by that system, and means for withdrawing non-condensable gases and condensate from the system and venting the gases, and means for collecting and returning the condensate from the several systems to the generator.

6. In a steam heating apparatus, a steam genorator, a header supplied with relatively high pressure steam from the generator, a plurality of separate distributing systems each supplying steam at sub-atmospheric pressures to different portions of a building, each system comprising a supply pipe, radiating means, 'a reducing valve in the supply pipe for controlling and adjusting the sub-atmospheric pressure of the steam supplied from the header to the radiating means, a return pipe through which non-condensable gases and condensate are withdrawn from the radiating. means, means for maintaining a substantially constant diflerence in pressure between the supply and return pipes, andmeans for venting the non-condensable gases, and means for collecting the condensate from the several systems and returning it to the generator.

'1. In a steam heating apparatus, a source oi steam, a plurality of distinct distributing systems each system comprising radiators, a supply conduit leading from the source and having branches leading to the several radiators, an exhausting means, a return conduit having branches leading from the radiators, the return conduit connecting with the exhausting means, traps at the outlets of the radiators, a reducing valve in the supply conduit, the exhausting means functioning to maintain a pressure differential between the supply and return conduits sufllcient to insure a :ilow of steam into the radiators and cooperating with the reducing valveto maintain the steam in the radiators at a sub-atmospheric pressure which is determined by the setting of the valve and which may be varied in accordance with the heat output desired in that particular distributing system, the reducing valves being located in a centralized group to permit of coordinated control of the several distributing systems.

8. In a steam heating apparatus, a source of steam, a plurality of distinct distributing systems each system comprising radiators, a supply conduit leading from the source and having branches leading to the several radiators, an exhausting means, a return conduit having branches leading from the radiators, the return conduit connecting with the exhausting means, traps at the outlets of the radiators, a reducing valve in the supply conduit, the exhausting means functioning to maintain a pressure differential between the supply and return conduits sufiicient to insure a flow oi. steam into the radiators and cooperating with the reducing valve to maintain the steam in the radiators at a subatmospheric pressure which is determined by the setting of the valve and which may be varied in accordance with the heat output desired in that particular distributing system, the reducing valves and the exhausting means being respectively arranged in centralized groups to permit of coordinated control oi the several distributing systems.

9. In a steam heating apparatus, a source of steam, a plurality of distinct distributing systems each system comprising radiators, a supply conduit leading from the source and having branches leading to the several radiators, an exhausting means, a return conduit having branches lead-' ing from the radiators, thereturn conduit connecting with the exhausting means, traps at the outlets of the radiators, a reducing valve in the supply conduit, the exhausting means functioning to maintain a pressure differential between the supply and return conduits suflicient to insure a flow of steam into the radiators and cooperating with the reducing valve to maintain the steam in the radiators at a sub-atmospheric pressure which is determined by the setting of the valve and which may be varied in accordance' with the heat output desired in that particular distributing system, the reducing valves being located in a centralized group, and a centralized group of means positioned adjacent the grouped valves for indicating the temperature CLAYTON A. DUNHAM.

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