US1222071A - Safety-valve. - Google Patents

Description

Patllted Apr. 10, 1917.

a sains-SHEET 1.

G. H`.-CLARK. SAFETY VALVE.

APPLICATION FILED FEB. 9. 1916.

Patented Apr. 10, 1917.

LQQQWL m 4 SHEETS-SHEET 2.

G. H. CLARK.

SAFETY VALVE.

APPLICATION FILED FEB. 9. 1916.

Patented Apr. 10, 1917.

4 SHEETS-SHEET 3.

G. H. CLARK.

SAFETY VALVE.

APPLICATION FILED FEB. 9, 191e.

Patented Apr. 10, 1917.

4 SHEETS-SHEET 4.

GEORGE HALL CLARK, OE CAMBRIDGE, MASSACHSETTS, .AssIGNOE TO CEosB-Y ST j GAGE a VALVE COMPANY, OE BOSTON, MASSACHUSETTS, A CORPORATICN ou i CHUSETTS.

SAFETY-VALVE.

Specicatio ers Patent. lpwlbntill Aplt. IC', 1917.

' l Application led February 9, 19.16. Serial No'. 77,318.

To all lwho/m, t may con/cem.'

Be it known that I, GEORGE HALL CLARK, a Citizen of the United States, and resident of Cambridge, in the county of Middlesex and State of Massachusetts, have invented newA and useful Improvements in Safety- Valves of which the following is a specification.

. My invention relates to safety valves, and is addressed to the following` main objects:

First: Increase in eiiciency and capacity of delivery of steam or other elastic fluid under pressure.

Second: Maintenance of discharge-eiliciency and Capacity independently of variations in back pressure .within wide limits;

Third: Confinement of blow down within permissible limits;

Fourth: Control, by adjustment, of the warning of a safety valve;

Fifth: Freedom fro-m shock etre-seating, notwithstanding high valve-lift- Sixth: Double or cumulative pop with resulting sustained lift and consequent capacity to respond to accumulating pressure.

In the drawings hereto annexed, which illustrate my invention,- 4

Figure 1 is a diagram showing a standard orilice, and graphically indicating pressure conditions in such anxorifice;

Fig. 2 is a diagram showing a modification of a standard orifice, and graphically indigating pressure conditions in such an ori- Fig. 3 is a diagramshowing the manner in which a valve disk and its base may be Shaped to'provide a standard orifice,

Fig. 4 is a fragmentary sectional view, showing the relation of lift to delivery capacity, in a valve such as illustrated in Fig. 3;

Fig. 5 is afragmentary sectional view of a standard orifice valve disk and base, with an adjustable blow down ring incorporated in the base;

Fig. `6 is a diagram illustratinga cylin-A drical Standard, orifice corresponding in respect to cross-sectional areas to lthat producible by the annular orifice shown in Fig. 5, and graphically indicating pressure conditions therein at 'low or initial' valve lift;

Fig. 7 is a diagram illustrating thesamestandard orifice and graphically. indicating'pressure conditions therein at high, or final, lift; i'

Fig. 8 isa fragmentary sectional view of in pressure due to expansion,

a standard orifice valve disk and; base,

with two concentric adjusting rings incorporated in the base; l

Fig. 9 is a diagram approximately illus- A tratin'g by an equivalent cylindrical orifice,

the conditions subsisting ina-valve such as shown in Fig. 8, and graphically indicating the,distribution of pressures at low, or initial lift;

Fig. 10 1s a similar diagram, indicating approximately the conditions and distribution of pressures at high, or final, lift;

Fig. l1 is a diagram indicating more ex actly than'Fig. 9, the conditions subsisting in a valve such as shown in Fig. 8, at low or initial lift;

Fig. 12 is a similar diagram, illustrating the conditions subsisting at full lift; and

Fig. 13 is a vertical central section of a complete safety valve, which embodies the features illustrated by the preceding figures. The cardinal feature of my inventiony is the provision, and substantial retention, notwithstanding the employment of sundry fac-y tors of modification, of what I shall riesig- A nate as the standard orifice in a safetyv v valve.

A standard orifice, illustrated in Fig. 1, is one in which elastic fluid esca-pes under pressure at maximum delivery for the minimum cross section of the orifice, entirely fills all parts of theorifice, and exerts maximum aggregate pressure on the sides of the orifice throughout its length,-pressure which is substantially uniform throughout the length of the orifice-save for reduction at and near the discharge end.

It is well known, that if the curve of approach into an otherwise ,cylindrical orifice,

has a radius substantially and preferably not less than the diameter -of the orifice itself, the discharge of fluid under-pressure through the orifice-will be a maximum; and that the pressure at the throat of the orifice, z'. e. where the curved surface of approach `\self, is ap roximately 60% of the absolute pressure o it flows, and that this pressure at the throat steam will until at the y throat m the pressure becomes 60% of the tangentially joins the cylindrical orifice it- .g

the fluid in the space from which'r lis maintained on all parts of the orifice ex- V age) of 100 j with progressive reduction absolute boiler pressure, or, 54.1 lbs. gage pressure. f

The gradual fall in pressure from c to m is indicated in Fig. 1 by the sure which exists outside the -outlet o. The

pressure conditions from m to o, (assuming atmospheric pressure at o) are indicated in Fig. 1 by the line lw y z.

If the back pressure beyond and at the outlet o be raised, as to values indicated by s', s2, 88, s4, S5, s", the pressure and therefore the flow inthe standard orilice behind the point 'n will not be affected, until the back pressure is raised to a value in excess of the throat pressure under conditions of free flow, when the pressure conditions in the orifice will be as indicated by the dotted lines p S5 85 or p s6 s, according to the back pressure value. 7

Should the orifice be flared or enlarged from the throat m, as indicated in Fig. 2,

, to the seat S are, flow of steam in the pressure at m will be, as before, 60% of the absolute boiler pressure, but the pressures at points between m and n will progressively diminish. The distribution of pressures in such an orifice is indicated by the curve p lw y z of Fig. 2. Thus: for an orifice having any given minimum cross section,.the maximum aggregate pressure will be exerted in the orifice if it be a standard orifice, of uniform cross section throughout, save for the curved entrance.

As the delivery capacity of a given safety valve depends on the height at which it sustains its lift, the maximum lift-sustaining effect due to static pressure will be obtained by a` valve of which the disk and base are shaped to provide a standard orifice of uniform cross section. Maximum lifting force and maximum delivery capacity at all lifts, will thereby be secured, and will be conserved independently of variations in back pressure up to a value vequal to the throatpressure in the standard orifice.

In Fig. 3 there are shown, sectionally, parts of a disk and base, shaped to provide a standard orice. The disk D makes seatf ing contact with the base'B at the narrow annular region S. The sufaesofiapproach' in effect, curved tofsecure uninterrupted contact with these surfaces. 'These curved surfaces' of pproach are equivalent to those shown in lgs. 1 ald 2in relation to a cylindrical pressure curve l constant.

`disk and base were to contmue outward from orifice. A safety valve, provided with 'B will always `fill, and the escaping steam exert maximum lifting pressureon the lower surface of the disk D.

The effective seat ofthe valve, when the disk D and base B make steam tight contact, should be close to the throat of the i orifice, as at S. Though the surfaces B2 and D2 are shown as if they actually made contact with each other at all points when the valve is closed, in practice these surfaces should not make such complete contact, but should have a clearance space between them ,sufficient to insure that the steam tight seat shall always be close to the throat of the valve orifice. If, when the disk D lifts from the base B, the orifice is tobe a standard orifice as above defined, the cross-sectional v area of the passage from the throat (at S)y to the lips b and d at the outlet, must be kept If the meeting surfaces of the the seat in planes at right angles to the direction of lift, the orifice would-in effect be an expanding orifice, like that shown in Fig. 2, and while the curves of approach B and D would insure maximum delivery through the minimum cross Section of the orifice at .the throat (near S) the increase of the crosssectional areas, progressively toward the outlet, would reduce the total lifting pressure on the disk. In order to preserve substantial uniformity of cross-sectional area of orice, I shape the surfaces B2 and D2 so that the eective minimum sectional area between them shall b'e constant (or substantially so) at all points between the throat and lips of the orifice. This may be arl' ranged as sho'wn in Figs. 3 and 4, by shaping the disk and base so that the minimum section of orice at th`e throat shall be equal to the lift multiplied by the circumference,\ the mid-plane of the orifice at that point being perpendicular to the direction of lift, and thence curving the surfaces B2 and D2 at a progressively increasing angle to the said mid-plane. Thus (Fig. 4) the lift l being the same distance at all points of the disk, the orifice area 'at the throat will be Z multiplied by lthe orifice-circumference atl that radial distance, and at the lip b will be the distance t multiplied by the diskcircumference at that radial distance. Strictly speaking, l tor will be a mean between the inner and outer circumferences of the imaginary conical cross-sectional surface at t,

the circumference taken 'as the facf surfaces B2 and 1)2, will progressively di' minish from the throat to the lips of the valve orifice at any degree of lift. 1f Z be the maximum working lift of the valve predetermined by calculation, subject to empirical correction, the curves of the surfaces B2 and D2 should be so shaped that the orifice sections on minimum distances shall be equal at all points; thus theincrease of radius from the disk-axis is compensated for by decrease in minimum distance between the curved surfaces and the orifice becomes a true standard orifice at the lift Z predetermined as aforesaid. Under these conditions, the orifice is one of maximum delivery efficiency, and the lifting pressure on the disk is a maximum, being the same at all points between the throat and the point near the lips Ywhere the pressure declines toward the outside back-pressure value. And, unless back pressure in the region beyond the lips Z) and d rises to a value higher than 60% of the absolute fluid pressure below the disk, back pressure will have no diminishing'effect on the delivery capacity of the valve.

The condition of true standard orifice can be absolutely secured, with a disk and base construction as above described, only at' one value of lift Z; but the approximation to true standard orifice is-so close at smaller values of lift that practically the efiiciencies'of standard orifice are secured at all lifts. Stated accurately, the progression of condition is this: At initial lift, the value represented by throat-area divided by lip area is less than unity, and this value approaches unity as the diskapproaches the lift Z.

But, while high efficiency of delivery, maintenance of maximum lifting effect, and indifference to back pressure values up to 60% of the absolute boiler pressure, are secured by a valve constructed as shown in Figs. 3 and 4, such a valve would yin practice have a seriously large blow-down.

In order to correct the valve design to meet this important practical consideration, I modify it in the manner indicated in Fig. 5.

I provide a blow-down ring R, which, while it forms part of the base B, is adjustably mounted on the base by a thread-connection T. The curve B2 is formed on the ring R, and corresponds to the same curve, as shown in Fig. 4; but, for a purpose presently to be explained, this curve, and the corresponding curve D2 on the disk, is carried farther than before, so that both curves, at the lips Z) and (Z approach more nearly hfan before to parallelism to the direction of Suppose the predetermined or calculated maximum lift be Z as before. j The ring R is backed away from the disk D, to such a Vdistance thatwhen the disk D reaches the lift Z the orificenareaat the/lips will be equal to the orifice areal at the throat. There will then be a slight increase in orifice area at the step or shoulder formed at the threaded part T by the aforesaid adjustment of the blow down ring R. Nevertheless, at the lift Z the condition of standard orifice will be substantially produced, and the valve eficiency both as to delivery and maintenance of lifting pressure, will be'secured, as with the design shown in Fig. 4.

But, it will be perceived, at initial lift, the orifice area at the throat will be less than the sectional areaat any pointfrom the step or shoulder at T outward to the lips b, oZ. The value represented by throat-area divided by liparea will be less than unity at initial lift of the disk D, and as the lift approaches the predetermined maximum value Z, this ratio will approach unity, and attain it when lift Z is reached. Substantially, therefore, the progression of condition, with a I valve -as shown in Fig. 5, is the same as with a valve as shown in Fig. 4. The pressure conditions in the valve orifice at initial lift and full lift, are indicated in Figs. 6 and 7 In these figures, an orifice, of cylindrical character corresponding substantially with the orifice of the valve shown in Fig. 5, is diagrammatically illustrated, the diagrams being uniform in scheme with Figs. l and 2.

Fig. 6 represents the condition at initial v lift. The shoulder or enlargement at T (corresponding to T in Fig. 5) has the eect of bringing the outletfnear to the'throat of the orifice at low lifts and thus reducing the extent of true standard orifice. The area at b, UZ, is appreciably greater than the throat area. The pressure in such an orifice is indicated by the curve 79 w y e, 70 being the boiler pressure and w being 60% of p. Thev total pressure exerted on the sides of the oriice is represented by the area p lw y z.

As the lift increases, the condition illustrated in similar manner in Fig. 7 is progressively approached and finally assumed. Here the entire extent of valve-orifice has progressively approached and finally 'reached a closeapproximation to the condition of true standard orifice; ythe ratio between throat area and lip area approximates to unity, and the pressure curve becomes p 'w when the boiler pressure is reduced in slight degree by escape of steam, the valve disk descends a short distance. This descent, or

reduction of lift inmediately reduces .the total lifting pressure on the disk, inducing immediate further reduction, and so on, un-

' til the condition indicated by Fig. 6 is resumed, with this modiication,-that the boiler pressure p has by this time diminished, so that the area represented by m p fw y 2 (Fig. 6), is less than it was at the moment of initial lift. Therefore the valve disk D, under the pressure of its spring, closes on the base B.

' By moving the blow down ring up or down, the sectional areas of the valve orifice, from the throat outward, can be varied, and the aggregate effective pressure acting on the disk at theprogressive stages of lift can be ealtered. With the blow down ring backed For many situations, the extent of warning may be predetermined by so proportioning the valve base B that thedistance from the throat at S, to the threaded shoulder T yshall be great enough to afford the essential characteristics of a true standard orifice of suchextent that the aggregate pressure f v therein at initial stages of lift shall 'suffice to carry the disk D promptly toward its predetermined full lift'in 'response to a per# missibly small accumulatiomof boiler pressure'. The annular area between thev seat S and shoulder T may, therefore, be termed the warning annulus, sinceitsfextet/will determine the extent of warning given by the valve. To insure retention of theactual seat at S, where vthe throat of the orifice is located, the warning annulus should be given a slight clearance, so as not actually to touch the disk surface when the valve is closed.

I prefer, however, to construct the valve so that the extent of warning may be adjustably determined, and therefore to cor-A rect the standard orifice design for the purpose of reducing and adjustably controlling thel warning of the valve, I provide the modification of Jdesign illustrated in Between the blow down ring R and the seat S, I mount 'an adjustable warning ring W. The blow down ring R threaded at to the warning ring W, and thewarn-- ing ring W threaded to the base-B at T. 1By adjusting the warning ring W so that it .isf'nearly --ush with theA seat S, the seat# having no appreciable efect on the warning, while the adjustment of the warning ring W has, reciprocally, no appreciable effect on the blow down, provided the blow down ring is adjusted to produce a properly small blow down with the warning ring flush with the seat.

The pressure conditions produced at initial and full lift of a valve such as indicated in Fig. 8, are diagrammatically shown in Figs. 9 and 10, which represent cylindrical orifices drawn to thesame scheme as Figs. 1 and 2. In Fig. 9, which shows the conditions at low lift, the distribution of liftin pressure is expressed by thel curve p rw y 2, p being the pressure at which the valve is set to open. The orifice` divisions corre` sponding to the seat S, warning annulus or rin W and blow down ring R are designa d` by S, W and R, respectively. The

clearance produced by the adjustment of the blow down ring R produces a condition in which, at initial lift, the ratio expressed by area 'at m divided by area at o is a fraction considerably less than unity; there is consequently a marked drop in pressure at tw. Thus, if we assume that the aggregate pressure represented by the area p w y y 2 w just suffices .to hold the disk lifted a slight distance from the base, the valve will stand in the warning position until accumulation of pressure reachessay-the value p -(Fig. 9) when the total `aggregate pressure,

represented by the area pw y y z as, suffices to lift the` disk to full predetermined opening; this conditionbeing diagrammatically represented in Fig. 10. Here the area ratio area at m area at '0 L approaches more nearlygto unity than under area at m area at ois.less than unity at initial lift (because of the dliierence in radius at m and o respecmassacri tively) ibut becomes unity at the predetermined lift-value Z (because of the inclina-v tion of the surfaces I)2 and B2 to the direction of lift at the orifice-section t). 1f the curved surfaces 4D2 and B2, in a valve provided with a blow down ring, (Fig. 5) were the same in design and proportion as in Fig. 4, and the blow down ring were then backed away from the surface D2, the area ratio area at m area at o at the lift-value Z, would still be less than unity. Therefore, in a valve provided with a blow down ring, the curved surfaces D2 and B2 are? continued a little farther than in the case represented by Fig. 4, so that the further inclination of the curved surfaces will compensate for the initial clearance produced by backing off the ring R. By this means the valve will, at the predetermined lift-value Z, produce an area-ratio areay at rm.

area at o equal to unity, and thus attain' the condition of true standard orifice.

Y The diagrams, Figs. 11 and 12, illustrate they progressive pressure conditions produced by a valve, such as is shown in Fig. 8, more accurately than Figs. 9 and 10.

In 11, the\condition of warning at boiler pressure p, is indicated. The arearatio is here much less than unitybecause of the joint effect of greater radiusat o, land the backing off of the ring Rf.. VAccuririfiilation of pressure to p', let us assume, increases the aggregate pressure to a value suiicient to carry the disk to greater lifts. As the disk rises, the proportions and inclination of the surfaces D2, B2 at the lips of the orifice compensate progressively for the initialexcess oforifice at o (due to the backing off of the blow down ring R) and the area-ratio p area at m area at o l approaches `and finally reaches unity when the predetermined lift value Z is obtained. This condition is diagrammatically indicated in Fig. 12; the pressure diagram discloses a curve of the same .character as that .of Fig. 1..

improvements above described may be proportioned and adjusted to afford either of two specific modes of operation, in both of which the characteristics of standard orifice are conserved. i

Under some conditions, it is desirable to have a safety valve which will attain maximum lift under accumlating pressure, by means of a second pop, under other conditions, a valve may be demanded which will have a high sustained lift on the initial pop7 opening, and high discharge capacity at the popping pressure. In valves proportioned to afford the latter specific peculiarities in service, there will be no second pop, the lift increasing slowly under accumulation of pressure.

Within the principles of construction hereinabove described there are three variable factors; irst: the angle of inclination of the opposed surfaces of the disk and base, at the lips; second: the relative width of the two rings, and third: the initial clear ance of the two rings.

If'it be'desired to have the valve-disk settle back to a reduced lift after the initial pop, and afford high sustained lift under accumulation of pressure after a second pop, or quick rise from the original point of reduced lift, the warning ring should be rela-- developed to a steeper angle than in the case of a valve designed to give a single pop. When `so proportioned and adjusted, the valve will pop, with little or no warning, and immediately after attaining the initial pop-lift, will settle back to a relatively lower lift, at which the 'disk-sustaining pressure is effective over a surface substantially limited tothe area of the warning ring, because the blow down ring is practically out of` action by reason of its large initial clearance. If

then the boiler pressure accumulates so as ty lift the disk farther, the disk will rise slowly until the conditions of standard orifice progressively extend to the zone occupied by the blow down ring, and, when the condition of standard orifice is more nearly approximated in the blow down ring zone, the effective lifting pressure on the disk will increase and the valve will take a second pop to higher lift, when the standard orifice condition, being fully assumed over the entire orifice-surface, will cause the valve disk to be sustained at the high lift assumed. When the specific pressure in the boiler is relieved clearance.

reduced, the disk will continue to settle until the slight clearance of the warning' ring removes that ring from 1ift-sustaining action,

when the disk will descend abruptly v'to its' seat. This final closing drop of the disk does not take place until the more gradual descent of the disk has brought it very close to the seat; thus there will be no injurious hammering impact of the disk on its seat.

If, on the other hand, the conditions of use require a valve 'whi'chwill assume and sustain highlift at and after the initial pop, without subsidence of the disk (until discharge' has reduced the boiler pressure) the warning ring should be made narrower than for a double-pop valve, and should also be adjusted to. av larger clearance; the blow down ring will here have an initial clearance less than in a double'`l pop valve,both absolutely and relatively to the warning ring The width 'of the blow down i' 'ring will be greater in relation to the warning ring, and the angle of exit at the lips need not be so steep, as in the double pop valve. The sustaining power of the orificial pressure is afforded byd both rings after the firm pop, and the disk will not subside to the point where the warning ring alone is effective, except when the boiler pressure has been'reduced andthe valve disk is on its way to final closure. In such a single-pop valve, accumulation of pressure, while it will increase the lift, will not do so by any sudden increase or second pop.

If accumulating pressure should demand greater relief than the designed full lift of the valve affords, the disk will rise still further, producing a ratio p area at m area at o i which is greater than unity, and `Vthus causy 'so ing the orifice ,to depart proportionately from the true standard orifice. ciency of the valve will, under-such condi-` tions, be diminished, but the available discharge area will be increased, so that absolutely more weightpof steam per time-unit will be discharged, though at lower efliy ciency, than when the normal maximumdischarge was being Ldelivered at maximum standard-orifice efficiency` Intelligent selection of dimensions of a valve, with due regard for the maximum generative capacity.

ofthe boiler, will render such an abnormal condition of excessive lift quite improbable.

Y The ability to sustain high lift makes it feasible to employ a valve, designed according to the' principles herein explained, of

if that pressure then remains dimensions materially smaller than those of an. old-style valve of the same calculated 4 Huid pressure of the boiler has attained a value suiicient to start the disk from its seat, constant, the effect of. the standard orifice is to increase the total lifting force exerted on the disk, and, 4as the rise of the disk from the base produces a progressively closer approximation to perfectstandard orifice condition, this tota lifting force increases; so that with constant pressure at the inlet end of the orifice, the lifting effect increases in absolute value as the orificial area increases, and the discharge efficiency also progressively approaches the maximum at the predetermined full lift at which the standard orifice condition becomes perfected.

^ Also, when the valve disk, in response to diminution of boiler pressure, begins to descend, the total sustaining force becomes progressively depleted by reason of the departure from the condition of true standard o ice which characterized the position of tlie disk at the predetermined or calculated full lift, so that the pressure condition which initiatessubsidence of the valve disk is favorable to continuance of subsidence and ldisk and a base shaped to provide a standard' orifice of substantially equal oriicial area at throat and lips when the disk is at its predetermined full lift.

3. In a safety valve, the combination of a disk and a base shaped to provide a standard orifice ofv substantially equal orificial area at throat and lips when the disk is at its predetermined full lift, said orifice modilied by .an enlargement extending toward the lips from a reglon between throat and'li s.

4. In a safety valve, the combination o a disk and a base, shaped to provide a standard orifice, said disk and base provided with a seat of mutual engagement close rto the throat of said standard orifice.

5. In a safety valve, the vcombination of a disk and a base, shaped to provide a stan'dard orifice, of substantially equal oricial j orifice,

area at throat 'and lips when the disk is at 7. In a safety valve, .the combination of a disk and a base, shaped to provide a standard orifice, one of the members (disk or base) comprising a ring adapted to be backed away from the opposing surface of the other member, one of the lips of the valve orifice being on said ring.-

8. In a safety valve, the combination of a disk and a base, shaped to provide a standard one 'of the members (disk or base) comprising a ring adapted to be backed away from the opposing surface of the other member, one of the lips of the valve orifice being on said ring, and one of the members (disk or base) comprising another ring, adjacent to the throat of said standard orice, and adapted to be backed away from the `opposing surface of the` other member.

9. In a safety valve, the combination of a disk and a base, shaped to provide a standard lorifice of substantially equal orificial area at throat and lips when the disk is at predetermined full lift, one of the members (disk or base) comprising a ring adapted to be backed away from the opposing surface of the other member, one of thelips of the valve orifice being on said ring.

10. In a safety valve, the combination of a disk and a base, shaped to provide a standardorifice of substantially equal orificial area at throat and lips when the disk is at predetermined full'lift, one of the members (disk or base) comprising a ring adapted to be backed away from the opposing surface of the other member, one of the lips of thevalve orifice being'on said ring, and one of the members (disk or base) comprising'another ring adjacentto the throat of said standard orifice, and adapted to be backed away from theopposing surface of the other member.

11. In a safety valve, the combination of a disk and a base, and means to vary progressively the ratio betweenthroat orifigialarea and lip orificial area from a value less than unity toward unity as the valve opens.

l12. In a saft-ty valve, the combination of a disk anda base, shaped to provide a standard orifice, and means to vary progressively -the ratio between throat orificlal area and lip orificial are-a from a value less than unity toward unity as the valve opens.

13. In a safety valve, the combination of a disk and a base, shaped to provide a standard orifice, the opposed surfaces of said disk and base in the region of the lips thereof inclined to the plane of the seat, to equalize the orificial area at throat and lips.

14. 'In a safety valve, the combination of a disk and a base, shaped to provide a standard orifice, the opposed surfaces of said disk and base in the region of the lips thereof inclined to the plane of the seat to equalize the orificial area at throat and lips at a predetermined value of lift, said surfaces when the valve is closed being spaced apart from the lips inward toward the throat, to provide initial excess of orificial area at the lips over that at the throat.

15. In a safety valve, the combination of a disk and a base, provided with a seat of mutual engagement, an adjustable ring adjacent to and surrounding the seat, a second adjustable ring outside the first ring, said rings constituting parts of the said members (disk or base), the opposed surfaces of the disk and base shaped to form a standard orifice.

16. In a safety valve, the combination of a disk and a base, shaped to form a standard orifice, a seat of mutual engagement of said disk and base adjacent to the throat of said orice, the opposed surfaces of the disk and base spaced apart in an annular region adjacent to the seat, and still farther spaced apart outside of said annular region.

17. In a safety valve, the combination of a disk and a base, shaped to provide anv orifice of substantially equal orificial area at throat and lips when the disk is at a predetermined full lift.

18. In a safety valve, the combination of a disk and a base shaped to provide an orifice of substantially equal orificial area at throat and lips when the disk is at its predetermined full lift, said orifice modified by an enlargement extending toward the lips from a region between throat and lips.

19. In a safety valve, the combination of a disk and a base, shaped to provide an orifice of substantially equal orificial area at throat and lips when the disk is at its predetermined full lift, said disk and base provided with a seat of mutual engagement close to the throat of said standard orifice.

20. In a safety valve, the combination of ya disk and a base, shaped to provide an orithroat and lipts mined full 1i when the disk is at predeterone of the members (disk or base') comprising a ring adapted to be backed away from the opposing surface of the other member,

valve orifice being 22. In a safety a disk and a base,

one of the lips of the on said ring.

valve, the combination of shaped to provide an oriv ce of substantially equal oricial area at throat 'and lips w termined full lift',

hen the disk is at predeone of the membersdisk or base) comprising a ring adapted to be backed away from the opposing surface of the other member, one of the lips of the valve orifice being on said ring, and one of the members (diskor base) comprising another ring adjacent to the throat of said standard orifice, and adapted toy be backed away from the opposing surface of the other member.

Signed by me at Boston,

Massachusetts, this eighth day of February,

1916. GEORGE HALL CLARK.

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