US2088071A - Heating system - Google Patents

Description

July 27, 1937. w. TALLMADGE HEATING SYSTEM Filed March 16, 1935 INVENTOR m a ATTORNEY V certain two-pipe systems or to a system which Patented July 1937 UNIT D sT- ATE PATENT EQ'F E 1-1 claims. 40!. 23740) p Thisinvention relates to-a steam'heating sys-.

tem, and more particularly to what is known as a one pipe system,jalthough equally applicable to combines the one andtwo-pipe principles, and with special referenceto' the heating'of small and medium sized buildings where the steam is supplied to the radiators at relatively low pressures;

and one object of the invention is to improve the circulation and distribution of steam. to a group or radiators and tosoregulate the heat given off thereby as to enhance the comfort and healthp! the occupants, reduce the water noises, and effect an economy in fuel or steam, while "a further opject'is to provide a simple automatic temperature control whereby to effect with a single thermostat located in a key or-chosen position therein a moreuniform distribution of'the steam, and

' consequent equalization of the heat in all parts 01 a small building or building. i W i A one-pipe heating system may be described as consisting of a source of steam supply, either a boiler or supply main, a damper regulator or a valve fonregulating the pressure and consequently the flow of steam, distributing pipesand t risers leading fromthe regulator valve to'the radiators, radiator supply shut-off valves, radiator air valves, and drip pipes and a wet return pipe'or pipes. Q i

In ordinary everydaypractice such systems are installed for thesole reason that they are lower in first cost; and little has been done to improve their operation as compared with the improveequipped with'the usualon and off thermostatic control there is always a lag in' response to the thermostat-sometimes called "fly-wheel" effectcaus ng short periods of alternate overheatingand overcooling, which will be the more pronounced the farther away the radiator is located, and overheating'and overcooling effects will also be produced in'those remaining in use by the turning off and on of some of the radiators.

in a zoned section of a larger aware,the only regulation here- I have remedied these long known and long) outstanding defects in the one-pipe heating system and have improved the two-pipe system by; my present invention, which in its simplesttorm. comprises, essentially, control apparatus (such, for. example, as that shown and described in Letters Patent No. 1,935,166 lssuedto me under,

date of November 14, 1933, orsomemodification thereof), adapted to automatically regulate the supply of steam, whether from the boiler 01 a furnace or from a supply main, so as to shut it oif entirelyor to effect a flow thereof through the distributing pipe or pipes and to the several muators of the system under one of two or' more accurately defined pressures-1401 example, one apredetermined maximum pressure and a second some predetermined and preferably small, fractionthereofwhen and as required byItemperature conditions within the buildingor the zone to be heated, and, cooperating therewith, means permitting, the escapeioi' air from the main distributing pipe and radiatorsequipped with at least two air valves-aprimary air valve, which is located at or adjacent the inlet end of the, radiator not-at its outlet endas heretofore, and which preferably opensto allow the escape oi. air from the distributing and branch pipesunde'r a light pressure, slightly below that or the steam;

when supplied at the predetermined lowvpressure, and closes ,when reached and heatedbylthe steam, and a secondary air valve, 9. modification of the primaryvalve, which may be'and preferablyis located at or close to the lower corner 01' the outlet end of the radiator and isioperative to allow the escape of, the air therefrom only under a pressure approximately that oi the steam when supplied at the predetermined maximum pres-- sure, closes when reached and heated by the cessive stages, as follows: (1) steamis supplied 7 under low pressure to each radiator oi, the group with an escape of air through a iree flowing thermo float valve on the outer end of the dis-- tributing pipe and the primary air valve ,on'the radiator and so fills and heats the pipes and the radiator itself up tothis valve; (2) the steam,

after heating and closing this valve, and still under low pressure, partially compresses the air more of the surface of theradiator for the effective transference of heat. Then, when temperature conditions within the heated area call for less than full heating, the steam supply is cut off and is kept off for a period sumcient to allow the radiator to cool down and by the partial vacuum created by the condensation of the steam therein to draw in air through the secondary air valve to recharge the system with air, in readiness for a repetition, or partial repetition, of the cycle.

For a full understanding of the invention reference will be made to the accompanying drawing, in whicha Figure 1 is a diagrammatic view of a combination oneand two-pipe heating system, illustrating one practical embodiment of my improvements, as applied to such a system; Fig. 2 is a view, in vertical section and on an enlarged scale, of the air valve here used on the radiators as the primary air valve; and Fig. 3 is a view, similar to Fig. 2, of the upper part of the valve as modified to serve as the secondary air valve.

Refering to the drawing, and assuming that the system is designed to operate under a steam pressure of say eight ounces per square inch for full heating and of one-half ounce for partial heating, indicates the supply pipe or main through which steam is supplied to the system, and 2 is the regulating valve which controls the quantity thus supplied and which is operatively connected with and is actuated by the motor 3, here shown as a vapor-tension motor of standard make. From the low pressure side of the regulating valve the steam is conducted through a distributing pipe 4, provided with an ordinary check-valve 5, to admit air thereto upon the formation of the partial vacuum, to branch pipes or risers 6, 6 and thence through the usual steam shut-off valves I, to a plurality of radiators 8, 8 and 8 8, the radiators 8, 8 being additionally provided with return pipes 9, 9 to a water return main I which is provided as usual with an air-vented water seal trap The distributing pipe 4 is also connected at its outer end as usual to the water return main I0 by a drip pipe l2, and at least in the larger installations, with a free flowing thermo float valve |3. Each of the radiators is equipped on its inlet end with a primary air valve l4 and on its opposite or outlet end with a secondary air valve 15, the primary valve being preferably located as low down on the radiator as practicable and the secondary air valve close to the bottom thereof, especially in the case of the one- pipe radiators 8, 8.

Each primary air valve l4, of the thermo float type, consists of the usual outer casing Hi from the base of which projects a nipple l6, by which the valve is connected with a threaded opening in the wall of the radiator. The usual sealed and longitudinally expansible inner chamber containing the volatile substance, is suitably supported at the lower part of the outer casing and.

at its upper end carries a valve [8. And the screw plug I9, set into thehpper end of the outer casing, and cap 2fl together provide a seat for the valve 3, an air passage 2|, and an outwardly opening check-valve consisting of the valve chamher-22, ball 23 seating on the enlarged upper end of the passage 2|, and air passages 24, 24. The weight of the ball is so proportioned to the area of the opening on which it is seated that it will lift on a light pressure, say one-half ounce, sufiicient to force the steam the entire length of the distributing pipe 4 before it starts up the riser pipes 6, 6 to the radiators, thus insuring an even distribution of steam to the radiators whatever the length of the main distributing pipe. In tall buildings however, it will usually be found desirable to omit this ball, leaving the valve a free flowing valve, on the radiators of the top floor with an up feed and of the bottom floor with a down feed system.

The secondary air valves l are or'may be like the primary valves in all respects except that for the threaded plug l9 and cap 20 of the latter there is substituted a plug l9 and cap 2|) which provide a'passage 2| with seat for the valve l8, and two check valves-one opening outwardly and the other opening inwardly-consisting of lower "valve chamber 22 ball 23? seating on the upper end of the passage 2|, passage 24 connecting the top of valve chamber 22 with the bottom of upper valve chamber 25, ball26 seating on the upper end of the passage 24, by-pass 21 from passage 2| to upper valve chamber 25, and outlet-inlet passage 28 between passage 24 and the outer air. This valve functions, when the main valve I8 is withdrawn from its seat, to allow the escape of air through the passage 2|, lower valve chamber 22- and passages 24 and 28, but only when the pressure within the radiator is sufiicientapproximately eight ounces, the pressure required for full heatingto raise the ball 23 from its seat; and, on the shutting off of the steam and the cooling of the radiator, the partial vacuum thus created, lifting the ball 26 from its seat, draws in the outer air through the passages 28 and 24, upper valve chamber 25, bypass 21, and passage 2 I.

The valve actuating motor 3 is supplied with electric current, to heat its operating coil 29, from a'suitable source such as the secondary winding 30 of a small transformer, over circuits which include the conductor wires 3|, 32., 33, 34, 35, 36, 31, 38 and 39, and which may be, and in the embodiment of the invention-here illustrated are, controlled jointly by what, may be designated as a dual-controlled thermostat 40 and pressure-responsive device 4|, with a secondary control by the time clock 42 and timing device. 43, all as presently to be described.

The thermostat 4D has, as shown, three spring contact-fingers 12, II and Ill, suitably supported and carrying the usual contacts, and attached to the outer face of contact-finger 12 and forming part thereof is the usual bimetallic thermostatic element I2 so arranged that on cooling this finger bends to theleft and on heating bends to the right. The arrangement and adjustment of its parts are such that, with. a day-time setting at a mean room temperature of 72, for example, the contact-fingers will be in the relative position shown, with both sets of contacts open. If the temperature drops say one degree, to 71, contact-finger 12 will be bent to the left to an extent suflicient to close its contact against the cooperating contact of contact-finger II, and on a furing has not so raised the room temperature as to effect an opening ofcontact-fingers I and H, a new circuit will thereby be established through the heating coil of the motor, parallel to that above described, fronrwire 32, closedi contacts of switch 46, wire 36, coil wire.31,

contacts of switch 48, wire 38,, contact-fingers 10, II and 12 and wire 39. The motor, continuing to operate, will further lift the regulating valve and as the valve opens the pressure on the steam supplied therethrough to the radiators will be built up, opening the motor circuit at the contacts of switch 46 and further compressing the air bound within the radiators and heating up more of their surface, until it is sufficient to openthe secondary air valves l5, l5, whereupon with the escape of air therefrom the steam substantially fills and heats practically the entire heat transfer surface of the radiators. And, as before, the pressure-responsive device 4| serves'to hold the motor and valve closely to the position required to supply steam to the radiators at the predeterminedmaximum pressure for full heat, so long as the contacts of the contact-fingers I0 and H remain closed, by alternately opening and closing the motor circuit on variations of pressure slightly above and slightly below such maximum, preventing an over-supply of steam to the radiators. In case, however, the conditions are such that the partial heating of the radiators effects a rise in the roomtemperature slightly above 70 before the time clock closes'the contact switch 48, the closing of this switch will be without efiect since the new circuit through the coil of the motor closed thereat will 'be broken at the contacts of the. thermostat. Accordingly, the circuit con trolled by switch 45 of the pressure-responsive device will continue to so operate the motor as to hold the reducing valve in its position for partial heating. But if at any time this partial heating of the radiators so raises the room temperature, above say 71, that the thermostat opens the contact between its contact-fingers H and 12, the motor circuit will be broken and the regulating valve will drop and remain closed until the room temperature falls and the thermostat again closes contact between its contact-fingers H and 12, whereupon the motor will be started to again left the valve to restore the system to a condition of partial heating.

.Assurning, however, that the temperature conditions are such that a full heating of the radiators is required to raise the room'temperature to say 71, on a slight further rise the thermostat will open the contacts of its contact-fingers II and I2, breaking thereat the circuit through the heating coil of the motor, and so allows the motor to cool and the regulatingjvalve to close. But during every period of full heating the motor is controlled by the circuit which includes the contacts of switch 46' of the pressure-responsive device and the coil 5! of the timing device 43, and this coil so heats the bimetallic element 49 that it bends to the right out of contact'with the contact 50, thereby breaking at this point the operating circuit of the motor for partial heating which includes the contacts of switch 45 of the pressure-responsive device. Hence, on the breaking of the motor circuit at the thermostat after a period of full heating, the motor cannot again'be started, to lift the regulating valve, until after the lapse of the period required by the bimetallic element 49 to so cool as to bend back to the left and again make contact with contact 50, with the result that during this period of delay the radia tors will have had time'to so cool down and condense the steam therein as to produce a vacuum suiificient to raise the ball in the upper valve chamber of their secondary air valves and draw in outside air to restore them to condition for a resumption of partial heating, and later of full heating for and'asrequired and under control of the thermostat on the closure atthe contact 50 of the operating circuit of the motor through the contact switch 45.

The operative principle of the system, in whatever form it may be embodied for practical'use, is that the steam' supplied to heat the radiators is admitted to-the interior thereof in stages, fl'rst with moderate flow and under low pressure to the inlet end only of the radiators, and'iinally, if required by temperature conditions, at full flow and under relatively high pressure to practically the entire interior of the radiators.

By thus heating the pipes and radiators gradually, or by stages, I reduce to a very considerable I extent the heavy starting demandfor steam, and consequent abnormal amount of water condensate, characteristic of the ordinary one-pipe heating system, with the result that the pipe capacity. is not overtaxed and the condensate will, flow reducing to aminimum, the amount of the residual air which will be entrapped and bound therein; In consequence, I am able to promptly efiect, without lag or fly-,wheel effect, a substantially'uniform distribution of the steam to a group of radiators, regardless both of their location and of variations from time to time of the number thereof in use, whether at a low pressure for partial heating or at a higher pressure for full heating as selectively determined by the thermostat according to the prevailing weather conditions, and to accomplish all this with the elimination of most if not all of the water noises and a material saving both in first and in operative cost.

. While I have shown and described my improved system as controlled by a regulating valve operated by a vapor-tension motor, it is to be understood that an electro-magnetic motor, gravity motor, air, oil, or water motor, or motor power of any-suitable type, may be substituted therefor; and in case the regulating valve is of the type actuated by a screw-spindle the motor to be used therewith will of course be one adapted to effect a rotary instead of a reciprocating movement of the spindle. The desired regulation can also be effected, as hereinabove indicated, by operatively connecting the motor to the dampers of the furnace of a steam boiler as in my earlier patent.

It is also to be understood that, while the motor has been shown and described as jointly controlled in its operation'by a thermostat and a iorthe motor operative to eflect a. shifting of i may be varied as desired-higher pressures being required in installation for largebuildings and occasionally andunder special conditions even in small bulldings and 1 the pressure-responsive de-o vice, when used; neednot be associated with the distributing pipe as shown but may be operativeh! connected with the distributing system at any valve itself orelsewherefi g What I claim as newfand desire to secure by Letters Patent, ls-- '1. An automatic air valve for a steam radiator comprising a main float and thermostaticaldiiferential pressure and a one-way ball valve 1y actuated valve which is normallyopenand is closed by heat and/or water, andg mount'ed upon the outer end of the fixed valve membera cap providing passages connecting the outlet of the valve with the air-outside and controlled respec tivelyby a one way ball valve opening to permit the outward flow of' air under a relatively high opening to permit the inward i flow a light differential pressure. I

2 'In a heating system of the type describedthe combination with a source of steam supply and a plurality of radiators connected bypiping therewith, of meansfoperative to selectivelyprovide a substantially constant supply of steam from the supplysource to the radiators at one of, two predetermined pressures, either a low pressure for a partial heating-or a ;higherpressurej for, the full heating-of theradiators, and means operative on the starting up of the heating sys-ftem after a shuttingdown thereof to maintain the supply of'steam to the radiators at the: lower pressure for a predetermined timeinterval I before it can be raised to the higher pressure.

I I the combination, with a source of steam supply pressurefor a partial heating or at a higher pres-j sure for the full heating "of the radiators, and H I it-can beraised to thehigher pressure and the second operative afterthe end of aperiod at i "'3. In aheating systembf thetype described the combination, with a source of steam supply and a. plurality of radiators connected by piping therewith, of a motor actuated valve "controlling theadmission oi stearnjfrom the supply source to the radiators, and control means for the valve motor operative to effect a shifting of the valve adapted to maintain substantially constant the supply of steam Ito the radiators atjone of two,

selectively determined pressures? either "afllow heating system is started up after a. shutting down thereof to maintain the supply-of the steam T to theradiators at the lower pressure for a 'pre-' it can be raised y i again be supplied to the radiators.

determined time interval before to the higher pressure. y H

"4. In a, heating system if the type described and a plurality ofradiatorscomiected by piping ,therevvithQof means operative to selectively pro 60 vide a substantially constant supply of steam from the supply source to the radiatorsatone of two predetermined pressures, either" a lowpressure for a partiafheating or a higher pressure for the fullheating of the radiatorsfiholudf-j ing timing means operative; to interpose a preperiod" at which the steam has been supplied to i the radiators atthehigherfpressure before the "steam can again be supplied thereto.

5. In a; heatingsystem of the typede nbed the combination, withia source of steam supply a and a plurality of radiators connected by piping I therewith,of ajvalvecontrolling the flow, of the steam [from the supply source to'the radiators, V a.

75 m tor tcontrollingjthe valve, and control ineans suitable point, as on the low pressure side of the the steam has'been suppliectto the radiators at; the higherypressure to interpose a predetermined. time interval before the steam can again be of Z air under the valve adapted to maintain, the supply of higher pressure for the full heating of the ra-. diators, said control means includinga timing device operative after the end of a period atwhich' 1 supplied theretm 1 V 6, In a heating systemof the typedescribedthe combination, witha source of steam supply and-a plurality of radiatorsconnected bypiping therewith, of means operative to providea supply"of"the steam to the-radiatorssubstantially;

constant at one of two selectively determined pressures, eithera l'owpressure for apartialnor I a'higher pressure'for the full heating'of them- .2

diators, timing means operative-on the starting ing which thesteam will be supplied to the radiatorsat the lower pressure before it can be supplied theretoat thehigher pressure,'and a second timing' means operative after the 'end of a period at whfihthe steani has'.,been supplied up" of the system after'a shutting-down thereof I to interpose a predetermined time interval durto theradiatorsiatthe higher temperature to interpose a predetermined time interval before the steamican again'be suppliedto the radiators. '7. In a heating system of the typedescribed the combination, with a source of supply and a plurality of radiatgrggeonnected by piping therewith, of a valve contrcilingthe flow of thesteam fromthe supply source to the radiators, a motor controlling the valve, andzcontrol means for the motor including a thermostat responsive to tem perat ure in the area heated by the "radiators and a pressure device responsive to pressure 'on' the low pressure side of the valveoperative to maintain a supply of the steam to theradiators"subs't'antially constant at either one of two given pressures as selectively determined by the temperature responsive device, and two timing means one operative on thestartingup ofthe system after a" shutting down thereof to-mairitain the supply of steam tothe radiators atthe lower pressure for a predetermined time interval before determined time interval before'ithe steam can 8, "In a heating system ofthe type described" the combination, with a source ofsteamsup'ply therewith, of automatic means for securing either a substantially equal partial "heating aria substantially equal full heating of all the radiators ing the steam, at .a relatively lowjpressure to first thef-radiators and forsuppI ying. the la and means operative whenlafter a period of: full heating of the radiators a partial heating only i is required to interpose "a time interval between of the group as'selective'ly determinedabya de-i I vice. responsive to variations inthe' temperature, saidmeans including means ior'supply higher pressure-to-expel theair fro'rniand sub N stantially fill the entire bodies 'of the radiators, j

,thecutting'ofi and againlcuttingbn'of the'supply 1c" steam supplied to the radiators, electric circuits for said motor, control means for said electric circuits including a thermostat responsive to changes in room temperature and a pressure device responsive to variations in the pressure of steam in the piping to the radiators. operative to provide a substantially constant supply or steam to the radiators at one of two predetermined pressures as selectively determined by the thermostat, and means including thermo air valves associated one with the mainline of piping and one with each end of the several radiators operative to allow the steam when supplied at the lower pressure first to expel the air from and fill the main line of piping and thereafter to expel the air from and fill the branch lines of piping to and the inlet ends only of the radiators and to allow the steam when supplied at the higher pressure to expel the air from and fill substantially the entire bodies of the radiators.

10. In a one-pipe heating system the combination, with a source of steam supply and a plurality of radiators connected by piping therewith ,of means for providing a substantially constant supply of steam from the supply source to the radiators at one of two selectively determined pressures, a thermo air valve associated with the inlet end of each radiator adapted to open to allow the escape of air therethrough only under a pressure approaching the lower pressure at which the steam is supplied to the radiators and to prevent any intake of air-therethrough, and .a thermo air valve associated with the outer end of each radiator adapted to open to allow the escape of air therethrough. only under a pressure approaching the higher pressure at which the steam is supplied tothe radiators and on the shutting off of the steam and the cooling of the radiator to permit the ingress of air therethrough.

11'. In a one-pipe heating system the combination, with a source of steam supply and a plurality of radiators connected by piping therewith, of means for providing a substantially constant supply of steam from the supply source to the radiators at one of two selectively determined pressures, a thermo air valve associated with the inlet end of each radiator adapted to open to allow the escape of air therethrough only under apressure approaching the lower pressure at which the steam is supplied to the radiators and to prevent any intake of air therethrough, a thermo air valve associated with the outer end of each radiator adapted to open to allow the escape of air through a one-way ball valve opening outwardly only under a pressure approaching the higher pressure at which the steam is supplied to theradiators and on the shutting off of the steam and the cooling of the radiator to permit the ingress of air through a second one-way ball valve opening inwardly, .and means. operative when the steam is turned off after a period during which it has been supplied to the radiators at the higher pressure to interpose a time interval before the steamis again supplied thereto sufiicient to allow theradiators to cool and become recharged with air. I

12. In a one-pipeheating system the combination, with a source of steam supply and a plurality of radiators connected by piping therewith, of

means for providing a substantially constant supply of steam from the supply source to the radiators at one of two pressures as selectively determined by the room temperature, a free venting thermo air valve associated with the main piping tothe radiators operative to allow the steam to expel the air therefrom and to fill the same at a pressure materially below the lower of the two pressures at which the steam maybe supplied to the radiators, a loaded thermo air valve associated with the inlet,end of each radiator operative to allow the escape of air therethrough at apressure approaching the lower of the two pressures at which the steam may be supplied to the radiators, and a loaded thermo air valve associated with the outer end of each radiator operative to allow the escape of air therethrough only at a pressureapproaching the higher, of the two pressures at which the steam may be supplied to the radiators, the air valve associated with the outer end of each radiator being adapted to permit the ingress of air through a one-way ball valve opening inwardly on the cooling of such end of theradiator. 1

13. In a one-pipe heating system the combination, with a source of steam supplyand a plurality of radiatorsconnected by piping therewith, of means controlled by devices responsive respectively to temperature and to pressure for maintaining the steam supplied to the radiators substantially constant at either one of two given pressures as selectively determined by the temperature responsive. device, means permitting the escape of air from the inlet ends of the radiators under the lower and from the outer ends of the radiators under the higher of the two said steam pressures, and means for recharging the radiators with air when after a supply of steam thereto at the higher pressures a supply at the lower pressure only is required.

14. In a one-pipepheating system the combination, with a source of steam supply and a plurality of radiators connected by piping therewitnoi a motor controlling theamount of steam supplied to the radiators, control means for said motor including a device responsive to variations in the room temperature and a device responsive to variations in the pressure of the steam in the piping to the radiators and adapted to selectively maintain the same substantially constant at a given maximum or at a given fraction of such maximum as selectively determined by the temperature responsive device, means associated with the respective radiators permitting the escape of air at their inlet ends only under the fractional and at their outer ends under a full pressure of steam, and means for delaying the supply of steam to the radiators at a full pressure for a predetermined period after a supply thereof at the fractional pressure on'starting the operation of the system.

15. In a one-pipe heating system the combination, with a source of steam supply and a plurality of radiators connected by piping therewith, of a motor controlling the amount of steam supplied to the radiators, control means for said motor including a device responsive to variations in the room temperature and a device responsive to variations in the pressure of the steam in the piping to the radiators and adapted to maintain the same substantially constant either at a given maximum or at a given fraction of such maximum as selectively determined by the temperatureresponsive device, means associated with the respective radiators permitting the escape of *air at their inlet ends only under the fractional and at their outlet ends under a full pressure of steam,

and means for recharging the radiatorswith air before steam can again be supplied to the radiators at the fractionalpressure after having-been supplied thereto at a fullpressure.

16. In a one-pipe heating system, the combination, with a source of steamsupply and a plurality of radiators connected by piping therewith, of a vapor-tension motor controlling the amount of steam supplied to the radiators, electric circuits for said motor, and control means for said electric circuits including a thermostat responsive at each temperature setting to at least three differ:

ent degrees of room temperature and a pressure device responsive to variations in the pressure of steam in the piping to the radiators adapted to maintain the pressure'oi steam to the radiators substantially constant at either apredetermined maximum or, at a predetermined fraction thereof as selectively determined 'by the thermostat, and

' air valves respectively connected with the inlet and outer ends of the several radiators, the valve at the inlet end of each radiator having. a main valve normally open and closed by heat and operwardly under a pressure through the main valve approximating the full pressure of steam and the other opening inwardlyunder a light pressure through the main valve.

17. In a one-pipe heating system, the combination,lwith a source of steam supply and a plurality of radiators connected by piping therewith, of

automatic meansfiir cludinga motor for supplying the steam to the radiators at either a prevariations in the room temperature, air valves respectively connected with the inlet and outer ends of the several radiators, thevalve at'the inlet end having-a main valve-normally open and closedby heat and a one-way subsidiary check -valve opening outwardly under a light pressure through the main valve and the valve associated with the outer end having a main valve normally open and closedby heat'and two one-way subsidiary check valves one opening outwardlyunder a pressure through the main valve approximating the maximum pressure of the steam and the other opening inwardly under a relatively light pressure through the main valve, and supplemental control means for the motor adapted to delay the supply of heat to theradiators at the'fractional pressure after a supply of steam thereto atthe:

maximum pressure, WEBSTER TALLMADGE.

way .subsidiary check valves one opening cutdetermined maximum pressure or a predeter mined fractionv of such maximum pressure as selectively determined by a device responsive to"

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