US1797258A - Steam trap - Google Patents

Description

March 24, 193.1.

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\ STEAM TRAP Original Filed Dec. 50. 1927 willIIII'IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIllllllllllll); -v/IIII'IIIII7IIIIIII -tvlllnllllIII/IIIlfllfllllllllllllllIIlIIIIIIIIIIllI/L uma/nu nun,

ing, wherein Patented Mar. 24, 1931 UNITED STATES PATENT OFFICE DAVID N. CROSTHWAIT, JR., OF MARSHALLTOWN, IOWA, AND CLAYTON A. I)'U1 IHAM,

0F GLENCOE, ILLINOIS, ASSIGNORS TO C. A. DUNHAM. COMPANY, OF MARSHALL- TOWN, IOWA, A CORPORATION OF IOWA STEAM TRAP Application filed December 30, 1927, Serial No. 243,578. Renewed September 11,1930.

a hermetically sealed expansible and contrac tible vessel or capsule containing a vaporizable fluid, and to the utilization of such traps for effecting the retention of steam in and the evacuation .of condensate and non-condensible gases from steam spaces, for example the radiators of a steam heating system. A steam trap in order to be efiicient must retain all of the steam in the radiator, or other steam space which it controls, without allowing any substantial portion of it to escape, and, on the other hand, must allow I water of condensation and non-condensible gases to drain out by gravity, to .be forcedout by the incoming steam, or be drawn out by a vacuum in the outlet pipe, depending upon the type of heating system with which the trap is used and upon the particular phase of its operation. For instance, in a vacuum steam heating system the condensate and air will ordinarily have to pass through the trap from a zone of higher pressure, the radiator,

' to a zone of lower pressure, the return pipe, when the system is under steam; but when the system is cold, the trap, in order to operate effectively, must permit outflow by gravity of condensate from and to spaces which may be at substantially the same pressure. The altitude of the apparatus through variation in barometric pressure is'also a variable factor.

The primary object of the present invention has been to provide a steam trap which will meet these requirements more effectively than traps heretofore known, that is to provide, a trap which, without readjustments, will retain the steam against leakage and also allow substantially complete evacuation of condensate and non-condensible gases when subjected to external pressures varying over a very wide range extending below, as well as above atmospheric pressure.

The application of the invention to practice is illustrated in the accompanying draw- Fig. 1 is a view in side elevation of the radiator of a steam heating system provided Fig. 3 is a similar sectional View, the full lines showing the contour of thecapsule after it has been exhausted, and as it is at ordinary temperature, 70 degrees F., for example, the dotted lines illustrating the contour of the capsule, as manufactured, that is before being exhausted.

The mechanical features of the trap and its capsule are known, the invention dealing exclusively with the nature of the volatile liquid used and with certain other features incidental thereto. The invention is not, therefore, limited to any particular construction of trap or any particular form of capsule.

The trap, as shown in the drawings, comprises a casing 10 connectedto the radiator 11 by a nipple 12, and a corrugated flexible metal capsule 13 containing a volatile liquid 14, the capsule being adjustably secured to the cover plate 15 of the casing and provided on its under side with a. valve 16 adapted to engage avalve seat 17 having a port communicating with the return pipe 18. Steam is sup plled to radiator 11 through a supply pipe 19.

The capsule 13 is hermetically sealed and contains a liquid which vaporizes at a temperature below the minimum steam temperatures to which the trap is exposed. The expansible and contr'actible capsule is subject on the inside to the vapor pressure developed, on rising temperatures, by the vaporization of the liquid 14. On the outside it is subject to steam pressures in the radiator. The in- .ternal vapor pressures must exceed the exbe seen from the following table taken from Marks & Davis Tables and Diagrams of the Thermal Properties of Saturated and Superheated Steam, 1909, showing the comparative temperatures and pressures of saturated steam, the water phase employed in steamheating, the column at the left side of page Algolute Steam 8 am steam pressures temperaigg tures ,8 are nch 125 1. 9 140 2. 9 161 4. 8 176 6. 8 187 8. 8 196 10. 7 205 12. 7 212 14. 7 218 16. 7 224 18. 7 230 217 235 22. 7 239 24. 7 24s 26. 7 24s 28. 7 16 lbs per square in- 252 30. 7 18 lbs. per sguare in. 255 32. 7 20 lbs. per square in. 259 34. 7 22lbs. per square in.-- 262 36.7 24 lbs. per square in. 265 38. 7

The above figures are based on a standard barometer of 29.921 inches of mercury or approximately 14.7 lbs. per squa're inch atmospheric pressure. Inasmuch as there is no single known substance wliich volatilizes at a point sufficiently below the boiling point of Water to give an excess of internal pressure that will effectively expand the capsule of a trap and move the valve to its seat, and which has vapor pressures paralleling the vapor pressures of water over the range of temperatures such as given above, and which will in other respects fulfil the requirements of a volatilizable fluid for the capsule, it has been-necessary to find a mixtur solution or compound. which will serve the purpose. But before approaching this primary requirement the several variable conditions which have to be considered in the making of'the trap will besule so as to. corrode it or impair its elasticity, or injure the seal between its metal parts.

(3) The liquid itself must not be impaired throu h chemical reactions set up between it and t e metal of the capsule or the solder or fluxes used in manufacturing and sealing the capsule.

(4) The vapor should be a saturated vapor for all working temperatures. That is, at all temperatures to which the instrument is subjected there must remain some unvolatilized liquid in the capsule. If, as in some 7 types of thermostatic traps, the amount of liquid is so small that all of it is volatilized at the higher temperatures of the working range, the vapor will be unsaturated at such higher temperatures so that its'pressures will depend not only upon temperatures, but also on volumes which latter increase, necessarily, as the capsule expands. sure of a saturated vapor is independent of changes in volume. Hence by using a vapor which is saturated for all working temperatures this variable factor may be eliminated.

a boiling point sufficiently below that of Water to develop at all working temperatures a vapor pressure sufficient to expand the capsule and set the valve firmly upon its seat. In practice, for a capsule of the type shown in the'drawingsthis excess of internal pressure over external pressure, for each tempei'ature of the range of working temperatures, should be about 11 lbs. per square inch; although it will be understood that the required internal pressure may be more or less in accordance with the mechanical structureof the instrument and the service which it is called upon to perform.

(6) The liquid must have a low specific heat (coefficient of thermal capacity) in order that it may respond sensitively to temperature changes.

(7) .T he liquid must have a low latent heat of vaporization for the same reason.

(8) The liquid must have a high coeflicient of conductivity also for the same reason.

(9) In the manufacture of the traps the capsules must be adjusted to compensate for variations in elasticity of the metal so that this factor will be uniform for all instruments. The adjustment of the capsules may be accomplished in accordance with the method described in the copending applica- The vapor pres- (5 The liquid must have, as stated above, Y

tions filed September 30, 1925, Serial No.

pand by internal air pressure; and also so that under all pressure conditions the expansion will be due substantially entirety to the internal vapor ressure developed and not to any considerab e extent to pressure of air. In practice a vacuum within two inches of the barometric vacuum is obtained. In any case, the presence of the residual air in the capsule, even tlfough the quantity is small, must be taken into account in the selection of the liquid mixture, since this residual air will expand less on rising temperatures than will the vapors developed from the liquid. A higher vacuum than that'abo've mentioned might be obtained, except for the cost, and in su ch case the liquid mixture will necessarily be altered slightly to compensate for the diminished quantity of air.

(11) Finally, the component liquids must be selected so that for every temperature Within the working range'the excess of internal pressure over external steam pressure will be approximately constant and this can be most efiectively accomplished by using components which are miscible or soluble with eachother in the proportions used at all operating temperatures rather than by using liquids which are not mutually soluble at all or some temperatures within the operating range. However, the excess of internal pressure need not be absolutely constant. In

act it is. preferable that the internal vapor pressure curve should not exactly flparallel the external steam pressure curve. The 1nternal pressures may deslrably increase slightly over the external pressures and so provide the additional force necessary to compensate for the velocities of the outgoing fluids which increase disproportionately, that is as the squares of the pressures, in relation% to the increase of radlator pressures, the pressure in the return or outlet pipe remaining ordinarily substantially constant. By describing the excess of internal pressure over external pressure as approximately or substantially constant for all temperatures of the working range, we do not intend to exclude the slight and desirable increase of internal over external pressures above referred to.

The selection of components for the liquid 5 for the capsule is made in accordance with the following principles: (a) when liquids are mixed which dissolve one in the other,

partly or wholly, the vapor pressure of the Any of the liquids suitable for use in thermostatic traps, if taken singly, will, within a single liquid is used the excess of its vapor pressure over thevapor pressure of saturat ed steam, if correct for a low temperature will be too great for a high temperature, and if correct for a high temperature, will be too small for a low temperature; with the result that the valve of the trap will not open or close properly and at the right time except at temperatures within a relatively narrow compass. In accordance with the invention one otherwise suitable liquid for the trap is mixed with another, or with more than one other, in such proportions that, considering one liquid as a base liquid, the tendency oi its vapor pressures to increase with rising temperatures is partially offset byits solution with the other liquid or liquids to an extent sufiicient to give resulting vapor pressures for the mixture in excess of the vapor pressures of saturated steam by a constant amount, or approximately so, for all temperatures within the desired range. The approximation of the vapor pressure curve of the liquid mixture to parallelism with the vapor pressure curveof saturated water vapor is obtained by adjusting the proportions of the constituent liquids in accordance with known or readily obtainable data as to the solubilit-ies and vapor pressuresof the liquids concerned, and in accordance with the well known laws governing the vapor pressures of liquid mixtures, to give a liquid mixture having the desired-vapor pressures for each temperature within the range of the trap.

For example, for steam pressures from a, vacuum of 25 inches of mercury to 25 lbsqper square inch above atmosphere excellent results have been obtained by a mixture consisting of chemically pure benzene (C H 99.5% by volume and denatured alcohol,

United States Treasury Department Formula No. 30, 0.5%; the denatured alcohol consistin of ten parts by, volume of ethyl alcohol ((ZH 'OH), and one part of methyl alcohol (QH OH), the total amount of alcohol being 95% by volume and the balance water.

The presence of the small quantity of water in the alcohol should be taken into account. It tends to increasethe vapor pressure of the mixture at the lower temperatures of the range where the vapor pressures of the benzene are too small. Benzene and alcohol are mutually soluble, substantially at all working temperatures of the instrument. 1

Water is only slightly soluble in benzene at the low temperatures, but becomes more soluble as temperatures rise so that its eifect is practically nil at the higher temperatures, at which the vapor pressure curve for bens zene is too far from the vapor pressure curve of saturated steam, the Water vapors at these high temperatures being absorbed in the base liquid or solvent. The eflect of the alcohols, in the proportion stated, is to modify the vapor pressure of the benzene at both ends of the range of temperatures to make the vapor pressure curve more nearly parallel with the curve representing steam pressures.

The effect of the residual air in the/capsule is to increase the pressure Withinthe capsule at the lower temperatures Without proportionate increase at the higher temperatures, since the rate of increase of the pressure of air, With rising temperatures, is very much less than the rate of increase of the vapors of the contained liquids.

Analogous results can be obtained by the use of difi'erent constituent liquids in dilferent proportions, the same principle of compensation howeverbeing utilized. For example, one can employ distilled Water 71.5% by volume, denatured alcohol (Formula No. 30) 28%, and benzene 0.5%.

It will be observed that this formula Water and alcohol are used in large amounts and benzene in a relatively minute quantity. The principle involved in making this and other possible compounds of these or different constituent liquids is the same as that which dictated the proportions of the first specified formula. Guided by this principle the selection of particular constituents and the determination of their proportions will be a mere matter of routine chemical laboratory Work. Where difierent constituents are to be employed care should be taken to select liquids that Will comply with requirements stated under captions (1) to (3) and (5) to (8) above. Enough liquid mixture should be used so that some will remain unvolatilized at all Working temperatures. The air should be exhausted from the capsule before it is sealed preferably to produce as high a vacuum as possible, The amount of residual air should be determined, and the efiect of its presence on vapor pressures compensated for all temperatures of tma working range.

Claims: a

1. A steam trap comprising a valve and an expansible and contractible capsule to operate the valve containing a mixture of, by volume, approximately 99.5% benzene and 0.5% of denatured alcohol of United States Treasury Department Formula No. 30.

2. A steam trap comprising a valve and a sealed expansible and contractible capsule for operating the valve which is substantially evacuated of air and containing such quantity of a mixture of approximately 99.5% by volume of benzene and 0.5% of denatured alcohol of United States Treasury Department Formula No. 30, that the vapor developed by application ni heat to the capsule Will be portions that the internal vapor pressures will be in excess of the vapor pressures of saturated steam by an amount constant for all temperatures correspondin to steam pressures from avacuum of appr ximately 25 inchesof mercury to a pressure above atmosphere of approximately 25 pounds per square inch.

4. A steam trap comprising a valve and a I sealed expansible and contractible vessel to operate the valve, substantially evacuated of airand containing, in an amount to give a saturated vapor for all operative temperatures of the instrument, approximately 99.5% by volume .of-benzene, approximately 0.05% of methyl alcohol, minute quantities of air and Water, and ethyl alcohol to make up 100%.

DAVID N. CROSTHWAIT, J R. CLAYTON A. DUNHAM.

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