US1233752A - Safety-valve. - Google Patents

Description

G. H. CLARK. SAFE TY VALVE. APPLICATION mp0 MAR.31,1916.

Patented July 17, 1917.

enonen HALL cLAnx, or CAMBRIDGE, MASSACHUSETTS, ASSIeMon To cnosnx STEAM eAen & vALvn COMPANY, or BOSTON, ASSACHUSETTS, A ConroaATmM or MASSA- CHUSETTS.

SAFETY-VALVE.

Specification of Letters Patent.-

Patented July it, 191?.

Application filed March a1, 1916. Serial No. 87,973.

To all whom it may concern Be it known that I, Gnonon HALL CLARK, a citizen of the United States, and resident of Gambridge,'in' the county of Middlesex and State of Massachusetts, have invented new and useful Improvements in Safety- Valves, of which the following is a specification.

My invention relates to Safety valves, and consists of improvements by which the discharge capacity of safety valves may be substantially increased without detriment to other valuable or essential characteristics of the valve.

Theoretically, the ideal safety valve would possess discharge capacity equal to the unobstructed discharge capacity of the orifice in the boiler or other container of elastic gas under pressure. This ideal has never, so far as I am informed, been realized, but it has figured in the speculations of engineers and inventors as the full-opening safety valve. Nor, so far as I am informed, has any theoretical design for a full opening safety valve been contrived which would, even theoretically, conserve the practically essential characteristics of a safety valve, which, to satisfy engineering requirements should assume and maintain full lift, close with a small permissible blow down, and

have only a limited period of warning at initial lift.

My invention herein described enables the engineer to design theoretically at least a full opening valve without detriment to the essentlal and valuable characteristics diemanded of a safety valve in practice. While it may be that a complete realization of the ideal full opening valve may be difficult, perhaps impossible because of practical constructive limitations,,nevertheless my invention renders it practically ossible to design and construct a safety va ve which will in operation approach closely, if it does not attain, to the ideal conditions of the full opening valve.

Sundry controlling or qualifying conditions should be noted as having general bearing on'the design of a full-opening safety valve, either in the theoretical or practical aspect.

First: As a valve disk rises toward its maximum opening, the point of pressure control gradually recedes from the valve seat-toward the inner extremity of the hole the effective sectional covered by the valve disk. That is to say: When the valve disk is seated, the pressure at the seat is the full boiler pressure; this full pressure is controlling at the initial lift of the disk, but as the disk rises and the valve orifice enlarges, the pressure at the seatfalls; if the maximum opening due to lift of the disk produces the condition of a full opening valve, the point of full boiler pressure will be found at the inner extremity of the hole in the boiler. 'Under such conditions the valve-opening will be simply a continuation of the discharge pipe, area of orifice being substantially equal at all points, whether in the pipe or under the valve disk.

From this it follows, that unless the entrance to the valve-controlled passage has the characteristics of a Standard orifice,

the valve as a whole will not be a full opendeveloped by the lifting of the valve disk is a true standard orifice, the lifting (and sustaining) static pressure on the disk outside the spring load area will remain the same for practically all values of lift of the disk.

Fourth: To secure full-opening conditions, some compensatory lifting factor must be enlisted to offset the diminution in lifting pressureon the spring load area of the disk, due to the fall in pressure at that point. p,

' Fifth: Forthe purpose of. compensation for diminution in pressure on the lifted disk, there is available the kinetic energy of escaping steam, full advantage having already been taken of the static pressure fac- 100 tors.

Sixth: If the design assumes the maintenance of standard orifice conditions, utilization of the kineticenergy of the escaping steam will not detract from the dischar e M5 capacity; no changes in velocity of flow W1 1 be involved.

As stated, the theory of design implies the provision of standard orifice, if conditions most favorable to the attainment of, or close Mt States v "1916, Serial No. 77,318, there is shown and approximation to, full-opening -valve are to be secured. In an application for United patent filed by me on February 9,

described a standard orifice safety valve. A standard orifice" is one so proportioned that an elastic gas under ,ressure (such .as

I steam) .will, in escaping t rough the orifice completely fill all portions thereof and exert maximum pressure on the sides of the orifice, this pressure being approximately 60% of the absolute pressure-1n the. container (such as the steam boiler) at-a point ad'- jacent to the throat or entrance into the orifice. This pressure is maintained on all partsof the orifice up to a point, near its discharge end, where the pressure diminishes jtoward the external r'essure- A cylindrical standard orifice w' l have a toric surface of approachwith a radius not substantially .less'than th'e diameter of the orifice itself, and this diameter will beuniform from throat to; lips Lgor discharge end). Thus, a standard or' ce.safety valve is one which, at a predetermined value of lift (by calculation subject to empirical 'correcvtion) provides an escape orifice which. is

completely filled'by escapingsteam, and of which the 'efiective cross sectional area at the throat (or entrance) is approximately l equal to the effective cross sectmnal area at the lips '(or dischiairgefend).

This standard 0 cc condition is fulfilled by a valve disk and base-having curved opposed surfaces which as they. increase radius from the valve. axis as a center, pro-- gressively approach parallelism to that axis.

These surfaces are toric. surfaces of revolution, developed by geometric rotation about the valve axis of a curve designed to secure the aforesaid equality-in cross-sectional orificialareas at the predetermined value of' lift.. At that value of lift a maximum liftmaintainingpressure will be exerted on the orifice-surfaces,ra-nd maxim-um discharge efliciency will be secured. But a valve of strictly theoretical standard orifice design fications of a sta invention.

will possess the practical defect of large" blow down, and should forthis reason depart slightlyfrom the-simple standard orificeconformat'gn. The practical modiwhich correct the esign in respect to blow down, and also in respect to warning,

without substantially impairing the standard orifice characteristics, are fully described in my aforesaid application for patent. Y In the drawing hereto annexed there" are shown in vertical section the parts of a safety .valve which relate particularly to my -D re resents ,the valve dlSk, on which the usual valve spring (not shown) exerts its effect. B is the base,

rd orifice safety valve,

lower portion of theformed in the valve casing. W- is the we ring adjustably screw-threaded on'the base B at T; R'is' the blow down ring, adjustably screw-threaded on the warning ring W, at T. Thelips of the valveorifice are at'the point d the valve disk D is 'rolon ed at the lip, forming the extension T e orifice from the boiler, formed in the valve casing may be provided with an entrance S, of toric conformation,

so-that the orifice normally closed by the valve disk will, if fully opened, have the essential characteristics of a standard orifice. If, however, the provision of a standard orifice entrance at this point should involve practical difliculties, it may be disfilesnsed with and the consequent reduction in charge efiiciency of the boiler-orifice endured. The valve orifice, however, should preserve standard orifice conditions in order to conserve the advantagesof maximum discharge efficiency and static lifting pressure. 7 4

-As fully set forth in my said a plication, the blow down of the valve is red permissible value by backing the ring R away from the opposite orifical surface, and

the amount of warning is adjusted to a desired value by bac the ring W away from vthe o posite orificial surface. The orificialsur acesare developed at the lippoint (i to a heater approach to parallelism to the'axis a, a, in order to compensate for the clearance produced by backmg off the ring R and toprorduce a proximate equality between effective orifici areas at the-throat and lip, respectively, of the valve-orifice at the predetermined full lift of the valve disk.

With a valve such as illustrated in the drawing, the disk, if lifted by the-pressure e f-steam, is in part sustained by the followingstatic factors: (1) the static pressure -exerted on the spring load area, and (2) the static-pressure exerted over the orificial area lying between the circumference, of the sprmg loadarea and the lip at d. If, as shown in application aforesaid, the curve pressure factors'are available, a full-open mg valve, or one closely approximating to full opening, cannot be obtained.

To compensate for the static pressure diminution due to lift of the valve and consequent relief by escape, I form the curved surfaces of the valve orifice so that the course of escaping steam is reversed, the disuced to a 3W closely to full-opening,

e verse direction of the 55 secured to the boiler b t5 shoulders,

% tially parallel, the direction of final discharge is the same for all values of lift. substantial parallelism between the orificial surfaces is a peculiarity of the standard 01'1- fice safety valve, a valve of this type lends W itself advantageously to the reverse-flow arrangement. The reactive lifting factor will be rovided, by so shaping tghe valve, that its ori ce produces a stream ischarge persist- V ently opposite to the direction of lift, preferably at all values of lift, and inclispensably at the higher values of lift. By providing a dischar site to thedirection of li the static pressure factors above mentioned e reverse or oppo- 2% a thlrd lift-sustaining factor, namely, the reactive efiect due to the direction of final discharge. The kinetic energy of the steam is thus enlistedthe reactive thrust in the direction of lift increases in quantity as the volume of steam per unit of time delivered increases and thus aflords a lift-sustaining factor which augments while the static pressure on the. spring load area diminishes. In order that the valve shall approximate due to utilization of the kinetic-energy of the steam must suflice to compen ate for the loss in static pressure on the spring load area and must further furnish an increment of 5 "energy to compress the valve spring.

The static and kinetic factors afforded by a standard orifice valve are such that a valve which closely approximates to the ideal full opening valve may be designed an well within the limitations imposed by practical structural requirements. In all cases, a lip-extension, as shown at E in the drawing, is to be recommended, since the .effect of such an extension is to conserve the re jet or" stream at high values of lift.

While, as intimated'above, a substantial measure of the advantages of a full opening valve will be secured even if the boiler orisa fice itself be not shaped to conform to stand- I ard orifice conditions, the full efliciency obtainable will require the provision of standard orifice conditions both in the boiler orifice and valve orifice. Thus, if the valve is means of a saddle, or reinforcing ring, such as indicated at F, the surfaces of the base B, saddle F and opening in the boiler shell A, should be shaped so that when all these parts are assembled,

to their adjoining surfaces will "form together a curved surface of approach, at S, which has a radius preferably not less than the fi diameter of the cylindrical orifice below the valve disk D. By eliminating all abrupt corners or edges, in the approach By making the opposed ori-' there is added to' the reaction-factor.

vmembers having to this boiler orifice, the entire passage, in cluding boiler orific and valve orifice, will,

when full-openingronditions are attained,-

become a standard orifice, capable of delivering the maximum quantity of steam which can pass through an orifice of the size of the orifice below the spring-load surface of the valve disk. I

What I claim and desire to secure by Letters Patent is:

1. In a safety valve, the combination of a disk member and a base member, the two members having opposed orificial surfaces forming, when the valve approximates to full opening, a standard orifice, the discharge of said orifice directed in reverse to the direction of lift.

2. In a safety valve, the cdfibination of a disk member and a base member, the two members .having opposed orificial surfaces to form, when the valve is open, an orifice of discharge in adirection reverse to the direction of lift, the disk member provided with 7 an extension in prolongation of the disk surface at the discharge end of the orifice.

3. In a safety valve, the combination of a disk member and a base member, the two members having opposed orificial surfaces to form, when the valve is open, an orifice of discharge in a direction reverse to the direction of lift, at the higher values-thereof, the, disk member provided with an extension in prolongationof the disk surface at the discharge end of the orifice.

4. In a safety valve, the combination of a disk member and a base member, the two members having substantially parallel opposed orificial surfaces to form, when the I charge end of the orifice.

5. In a safety valve, the combination of a disk member and a base member, the two members having opposed orificial surfaces to form, when the valve is open, an orifice of discharge in a directionreverse to the direction of lift at all values thereof, the disk member provided with an extension in prolongation of the disk surface at the discharge end of the orifice. V

6. In a safety valve, the combination of a disk member and a base member, the two posed orificial surfaces to form, when the valve is open, an orifice of discharge in a direction reverseto the direction of lift at all values thereof, the disk member provided substantially parallel op-v ice with an extension in prolongation of the T disk surface at the 7. In a safety valve, the combination of a dlsk member and a base member, the two discharge end of the orimembers having opposed orificial surfaces forming, when the valve approximates to full opening, a standard orifice, the discharge ofsaid orifice directed in reverse to the direction of lift, the disk member pro-- vided with an extension in prolongation of the disk surface at the-discharge end of the both of which possess the ewential characteristics of standard orifice.

9. A safety valve and its adjuncts, comprising a boiler orifice and valve orifice, both of which possess the essential charac: teristics of standard orifice, the orificial surfaces of the valve orifice being curved to form, when the valve is open, an orifice of discharge in a direction reverse to'the direction of valve-lift.

Signed by me at Boston, Massachusetts. 20 this29th day of March 1916.

GEORGE HALL CLARK.

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