US2643666A - Venting apparatus for tanks or the like - Google Patents

Description

June 30, 1953 J. F. LEE ETAL 2,643,666

VENTING APPARATUS FOR TANKS OR THE LIKE Filed May 6. 1947 3 Sheets-Sheet l 5 A INVEN TORS y ioeaiffli/vnm 2 4 96 ki dm Afro/(win June 30, 1953 J, LEE r 2,643,666

VENTING APPARATUS F OR TANKS OR THE LIKE Filed May 6, 1947 5 Sheets-Sheet 2 JNVENTORS wavy/71:5,

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Patented June 30, 1953 VENTING APPARATUS FOR TANKS OR THE LIKE Joseph F. Lee, Lynwood, and George E. Denny, Compton, Calif, assignors to Frank V. Long, Compton, Calif doing business as The Vapor Recovery Systems Company Application May 6, 1947, Serial No. 746,402 11 Claims. (01. 137- 248) This .invention relates to venting apparatus employing control valves for controlling the differential pressure between the interior of, a tank, and the pressure on its exterior. It concerns particularly, a type of control valve in which a bell is employed, that rises to break a liquid seal when a predetermined differential pressure exists between the external pressure and the internal pressure in the tank; and in the operation. of this type of valve, a valve-closure is employed for closing off flow through a duct that communicates with the interior of the tank when the said seal is broken. After the seal is broken, the parts composing the apparatus, cooperate to effect the opening of the valveclosure, and establish flow through the duct until the differential pressure returns to normal. Inv the type of valve referred to, the advantages of a liquid seal valve are obtained, combined withthe. advantages of a mechanical valve, that is, a valve having a mechanical part, which operates as the closure for the duct.

Control valves of this character, are of two types, usually associated with each other ona common fitting; and one of the valves functions when the pressure in the tank rises sufficiently to bring about a predetermined diiferential pressure, which must be relieved, by reducing it.

And the other valves operates to permit an inflow of air or gas from the exterior of the tank when a condition arises in which the internal pressure of the tank is below a predetermined point.

It is found in practice, that when the bell rises and breaks the liquid seal referred to, the admission of the gas under pressure to the duct and to the area of the valve closure that closes this duct, gives such an increase in lifting force to the bell, that the acceleration of its rising movement may, and usually does, develop an oscillating and erratic up-and-down movement of the bell.

One of the objects of this invention is to provide means for easing or dampening the rising movement of the bell after the seal is broken, so as to give a steady rising movement of the hell, that is occasioned by the admission of the internal pressure to the increased area, which determines the upward accelerating force acting on the bell, the general object being to effect a gradual opening of the valve closure without any oscillations or fluttering effect that is associated with a too sudden upward accelerated movement of the bell.

Another object of the invention is to provide a control valve apparatus having a construction which enables it to be readily adapted to incor- 2 poration in a vacuum pressure control valve, as well as a pressure relief valve, for relieving too great an internal pressure within a tank.

Another object of. the invention, as applied to a pressure relief valve, that is to say, a valve that functions to prevent too great a pressure existing within a tank, is to provide means for loading the bell soon after the liquid seal is broken, so that the rising movement of the bell beyond this point, will be dampened or cushioned. In this way, if the bell. rises sufficiently to engage limit stops that limit its upward movement, it will not strike these stops violently, butmove against them with a relatively slower movement, thereby preventing any sudden arrest of the upward movement of the bell from causing an inertia lift of the valve-closure from its seat; in this way, the opening movement of the valveclosure is made dependent upon the force exerted by the differential pressure on the two sides of the valve-closure.

Another object of the invention as applied to the vacuum relief type of valve, is to provide means for easing the rising movement of the bell, and to provide means associated with the valve, that can be regulated to set the bell to rise and break the liquid seal accurately at a given differential pressure. This feature enables a valve of the same diameter to be employed through a considerable range in the working differential pressure for the apparatus. 7

Another object of the invention is to provide a control valve employing such features as those referred to above, in a structure providing improved guiding means for the bell.

Further objects of the invention will appear hereinafter.

The invention consists in the novel parts and combinations of parts to be described hereinafter, all of which contribute to produce an efficient venting apparatus for tanks or the like.

A preferred embodiment of the invention is described in the following specification, while the broad scope of the invention is pointed out in the appended claims.

In the drawings:

Fig. 1 is a side elevation illustrating an outlet connection to be associated with a tanker the like, and illustrating a fitting connected with the outlet and carrying the two types of control valves referred to above, namely, a pressure relief valve for preventing the internal pressure of the tank from exceeding a predetermined amount, and a vacuum relief valve that operates to maingain{ a predetermined partial vacuum within the 3 Fig. 2 is a vertical section through a relief valve embodying this invention, and representing the bell in an elevated position, supporting the load or weight, and with the valve closure in an elevated position to open an outlet from the tank to the atmosphere. In this view portions of the apparatus are broken away. This view is an ideal section.

Fig. 3 is also a vertical section, and is similar to Fig. 2. This view shows the bell in its normal position when it maintains the liquid seal, and also shows the valve closure in its normal closed position.

Fig. 4 is a View similar to Fig. 3, but illustrating the vacuum type of relief valve.

Referring more partciularly to the parts, and especially to Fig. 1, the venting apparatus is indicated generally by the reference numeral I, and this includes a T connection 2 that is mounted on the upper flange of a flame arrester 3 that is usually provided above a tank carrying gas. This flame arrester is seated on a flange of an outlet d from the tank. One end of the T connection 2 supports the relief venting meansor pressure valve P that opens automatically to relieve pressure within the tank above a predetermined working pressure for which the plant is designed. The other end of the T connection 2 supports the venting valve V that functions to maintain a substantially constant pressure in the tank when the tank is operating under a partial vacuum working pressure. These two valves P and V are connected in position through suitable elbows and 6, the former of which presents its horizontal flange 1 in an upward position, and the other of which presents its horizontal flange 8 on its under side. The upper end of the relief valve P is of course open to atmosphere, and the vacuum valve V is open to atmosphere at its lower end.

Referring now to Figs. 2 and 3 that illustrate the pressure relief valve, its construction involves the use of a substantially cylindrical casing or shell 9, the lower end of which is welded or otherwise secured to a shouldered bottom head I0, which head is formed below into a reduced neck ll presenting at its lower end a substantially conical seat ii to receive the convex seat face I3. of an adapter ring or flange I4. This adapter ring I4 is connected by adjusting bolts l5 to the bottom flange [6 on the neck H, which can be tightened up individually so as to maintain the longitudinal axis of the cylindrical shell 9 in a substantially vertical position.

The head ii) is bored to present an annular shoulder Ill that operates as a seat for an inner shell H that extends up a considerable distance within the outer shell, and the upper edge of this inner shell ll operates as a seat for the bell 18. The inner shell I1 and the outer shell 9 cooperate to form an annular space operating as a launder carrying an outer permanent liquid seal at l9. This seal is referred to as permanent, because it is not the seal that is broken by the rise of the bell. This seal, however, permanently cuts off communication from the atmosphere to the interior of the bell.

Fig. 3 shows the bell l8 in its normal position of rest, at which time the cylindrical shell or apron 23 of the bell is maintained with its lower edge deeply immersed in the liquid, the level of which is indicated at l9.

The bell includes a flat plate-form head 21, the outer edge of which is secured by welding or brazing to the apron 2D. This head 2! has a concentric valve opening 22 formed through a valve seat 23 of annular form, which may be secured in place by machine screws 24, and these screws extend down through the head 2| and may be threaded into a flange 25, which is rigidly secured by Welding, or otherwise, to a central duct 26. On the upper side of the valve seat 23 a valve closure 2. normally rests, said valve closure being provided with suitable guiding means for guiding it whenever it rises from its seat. In the present instance, this is accomplished by' providing the upper side of the valve with a valve stem 28, which is guided to slide through the have 29 of a spider 33, said spider being supported on a plurality of posts such as the posts 3|. The annular outer ring of this spider 39 is attached to the upper ends of the posts 3| by suitable small screws or bolts 32.

The lower end of the duct 2'5 is preferably slightly flared outwardly at its lower end, to form a cone 33, the lower end of which dips into a fluid seal at 34, held in a sealing cup 35. This cup is preferably of bowl form, and supported on a plurality of legs or posts 36 seated on the bottom head ill. These posts operate to support the body of the bowl considerably above the inlet opening 3'! through the bottom of the head that connects to the flange 1 as illustrated in Fig. l.

The lower end of the cup 35 is drawn down to a blunt point 38 so as to streamline the gases that come up through. the inlet 31 before they pass through the annular passage 39 between the outer side of the cup and the inner shell ll of the casing.

The level of the liquid seal at 34 is indicated on a sight gauge 40, the lower end of which is connected to the interior of the bowl through an inclined tube 4| (see Fig. 3), and the upper endv of which is provided with a valve fitting 42 and an extension 43 above the same, that is connected by a small bent pipe 44 to the neck ll of the bottom head it) at which point it communicates with the interior of the inlet opening 31. The fitting 42 is secured at 45 to the outer side of the shell 9, but there is no communication through this connection at 45 to the interior of the casing. Through the medium of this tube 44, both ends of the sight gauge 49 carry the same gas pressure as the interior of the tank.

In order to guide the bell as it rises, the cup 35 is provided with a central guide stem 46, the lower end of which is threaded at 4'! into a threaded opening in the bottom of the cup. At an elevated point in the duct 26, radially disposed wings 48 are secured by welding or brazing, and the inner ends of these wings are attached to, and support, a guide tube 49 that slides on the guide stem 36 as the bell rises and falls.

We provide means for easing the movement of the bell as it rises and breaks the liquid seal at 34, and in the present instance, this easing means functions to load the bell immediately after the lower edge of the cone 33 has broken the liquid seal at 34. For this purpose (referring to Fig. 2), We provide a plurality of radially disposed plates 50, the upper edges of which are cut down to form seats 5| for a loading ring 52 (see Fig. 3), which normally rests on this seat. A lost-motion operative connection is employed between the bell and this ring 52, so that as the bell rises, it picks the ring up immediately after it has broken the seal at 34. For this purpose the loading ring 52 is provided with a plurality of upwardly extending stems 53. Each of these stems 53 is telescoped into the bore of a drag rod 55, the upper end of which is attached by a bolt 56 to the head 2| of the .bell'. The lower portion of'each'drag rod is formed'with two diametrically opposite slots '54 through its. wall, and each stem-53 is provided with a through pin-51, the ends of which run in these slots 54. With this arrangement, it is evident that when the bell has risen sufiiciently to enable the lower ends of the slots 54 to engage the pins 51, the weight of the ring 52 will be imparted to the bell. This is most advantageous, be-- cause as soon as the'seal at 34 is broken, the gas under, pressure from the tank, passes up around the cup and into the duct 26; This subjects the under side of the valve closure 2'! to the tank pressure, as well as the annular zone or area of the head 2| that surrounds the outer edge of the valve. This additional area under the tank pressure of course operates to accelerate the rising'movement of the bell. This would of course raise the bell rapidly, to the limit of its upward movement, and even drive it against the lower ends of a plurality of stops 58in the form of posts that project down from the under side of a cover 59,-or hood, that is attached-to the upper end of the outer shell or casing 9. Even if the rise of the bell is not sufiicient to move it against its limit stops 58, in practice, there is a tendency for the bell to oscillate up and down unless it is loaded, and this oscillation would naturally interfere with the proper lifting action of the valve closure 21, due to gas pressure.

In order to adapt the weight of the valve closure 2'l'to specification requirements, its upper face-is recessed so as to form a space to'receive a quantity of lead 69,. or other weighting'maa terial.

The cover orhood 591s of annular form with a downwardly bent concavo-convex marginal flange BI, and has a central opening, 52 over which a substantially conical bonnet 63 extends upwardly, and the interiorof which forms an expansion chamber 64 to reduce the immediate velocity of flow of gas that passes up throughthe open valve closure 21 and down through the annular outlet 65 that is formed between the lower edge of the flange GI and the upper edge of the shell 9.. The hood 59 is supported on: the posts 58 that are attached on the upper edge of the shell 9, and in the space between the upper edge of the shell and the body of the hood, a cylindrical screen 66 is secured in place so that it lies against the'outer sides of these posts.

The interior of the inner shell I! is provided with. meansfor guiding the flow of the gases that pass up around the cup 35when the bell has moved uphighenough to break the seal at..34, which gases pass up into the cone? 33 .as indicated by the arrows in Fig. 2, whichillustrates thebell inan extreme elevated position. For this purpose a substantially conical baffle 61 is provided, which is attached by machine screws 68, or in. any other suitable manner, to the inclined inner edges of the bracket plates 50 already described. When the bell is in its elevated position, the lower end of the cone 33 lies adjacent to the upper edge of the conical bafile 67 so 1 that the opening 69 at the upper end of the baflle, is in'the right positionto deliver the gases flowing upwardly into the gas duct 26. In addition to this, the flow of these gases is streamlined by providing an inner cone ill, the elements of which are concavo-convex. This cone "H1 is of shell form, and its elements are of concavo-convex form, and when the bell is in the elevated position shown in Fig. 2, the base of this cone nearly fills the area of the opening H at the upper edge or lip of the cup 35. This cone is supported at 6. substantially the same level as'the baffle 61, and is supported and centered by means of atubular shell '12, which is brazed or welded to the inner surface of the cone as indicated at 13. The lower end of this sleeve l2is stepped on a'base plate 74, to which it may be brazed or welded as indicated at 15.

The level of the permanent liquid seal indicated at 19, is indicated on the exterior of the apparatus by means of a suitable sight gaugelfi, the upper end of which is connected by a thimble TI to the interior of the shell 9, and the lower end of which is connected by a similar thimble 18 to the interior of this shell just above the bottom head I 0.

Referring now to Fig. 4, which illustrates a vacuum type of venting apparatus, it should be understood that it is not feasible to employ a weight for loading the bell, because the internal pressure of the tank is exerted upon the entire upper area of the bell, including the area of the valve-closure 19, Which is constructed and guided similarly to the Valve-closure 21 already described. However, it functions in the same way as the other valve-closure, to normally close 01? fiow of any gas from the interior of the tank through the central duct of its bell 8|. In this case, we employ resilient means such as ac-oil spring 82, which is mounted in association with other parts in such a way that under normal working conditions, when the cone 83 is immersed in the liquid seal indicated at 84, the spring 82 is under slightcompression, partially counterbalancing the weight of the bell and its attached parts. The upper end of this spring thrusts against a collar .85 that is rigidly secured to the outer side of a-guide tube 86 similar to the guide tube 49 alreadydescribed, and the lower end of this spring seats against the flange of a bushing '87 that is mounted loosely" on the lower end of the central guide stem 88 that corresponds to the guide stem 46 in the pressure relief valve already described. The lower end of this stem 88 is shouldered against a base plate 89, and beyond the shoulder it has a threaded tip 9i! that screws into a threaded socket in the bottom of the sealing cup 9|. The position of this bushing-"Bl can be adjusted up on the guide stem 88 to increase the upward thrust of the spring against the collar 35 to adapt this force to suit any setting for a predetermined point at which a partial vacuum within the tank will be relieved. In order to accomplish this, the lower coils of the spring 82 are centered around a tubular sleeve 92, which has two diametrically opposite slots 93, and the lower end of the stem 88 is formed with a central bore 94. A cross pin extends transversely through this bore 94, and its ends pass through the wall of the bushing 87, and are located in the slots 93. Against the under side of this pin, an adjusting screw 96 rests. This adjusting screw is threaded so that it can be adjusted up and down, and locked in any adjusted position. For this purpose'it may be provided with threads 91 that engage similar threads in the lower end of the threaded tip 99 referred'to'above; and in order to lock this adjusting screw at any point desired, it-is preferably provided with threads 98 atthe-pcin't where it emerges from the bottom end 99 of the streamlined bottom of the cup 9|. At this point the underface of the cup presents a seat for a lock nut I99 that is mounted on the threads 98; 'The lower end of this adjusting screw if desired, may be guided through the nave of a spider 10!, the annular outer rim N2 of which may be attached by small bolts I03 that secure it to the under side of the bottom head I04 of the outer shell I05 of the casing. These same bolts may be socketed into the lower ends of the legs or posts I06 that extend down'from the cup 9!. With this construction, it will be evident that by rotating the adjusting screw 96 in the direction that will advance it along at the threads 91, the pin 95 can be moved upwardly, carrying with it the bushing 81, the flange of which thrusts up against the bottom wrap of the coil spring-thereby increasing the compression force in the spring.

It should be understood, however, that this compression force in the spring is not great, and is intended to partially counterbalance the weight of the bell and its attached parts. The spider IiBI of course admits atmosphere through the opening I0'I in the bottom head I04, and this of course means that atmospheric pressure exists at the annular space I08 surrounding the duct 89, so that at all times the annular area on the under side of the head of the bell at I09, is exposed to atmospheric pressure. At the same time, as long as the liquid seal at 84 is maintained, the valveclosure 10 will be maintained closed by reason of its own weight, and by reason of the presence of the absolute tank pressure that is present in the chamber IIB and in the upper portion of the outer seal I 05 of the casing. In other words, communication is maintained from the interior of the tank through the adapter flange III that is connected up by adjusting bolts II2 to the flange of a reduced neck I I3 that is formed integrally with the upper head I I I of the casing.

For convenience in assembly, and for the pur pose of readily adapting the length of the outer shell I05 to requirements of specifications, the upper end of the shell I05 may include an adapter ring mm, the upper edge of which is attached at H5 to the lower end of the upper head Hi and this adapter belt or ring I05a carries a flange I I5 rigidly attached to it, that matches up with a similar flange I I! that is also welded or otherwise secured to the upper edge or the body portion of the shell I05.

The valve closure I0 is mounted and guided by means similar to that illustrated in Fig. 3, and its upper side is recessed to receive a lead filler II 8, the amount of which can be varied to adapt the valve closure to the required working vacuum that is to be maintained in the interior of the tank, and consequently, within the chamber IIO.

In the regular operation of this vacuum relief venting apparatus, when the partial vacuum in the chamber IIII approaches a minimum limit, the atmospheric pressure exerted on the annular area I09 will cause the bell to rise sufficiently to break the liquid seal at 84, whereupon the atmospheric air will pass under the lower end of the cone 83 and pass up through a choked annular passage I I0 between the edge of the crown cone I20 that corresponds to the cone 1!) already described. By choking the fiow of the atmospheric air at this point, we prevent too sudden a rise in pressure Within the interior of the duct 00, and thereby bring about a more-deliberate and easy upward movement of the valve closure 19. However, as the bell rises, of course the flared form of the cone 83 quickly increases this choke area through which the atmospheric air passes upwardly; and when the bell rises to the limit of its upward movement as determined by the location of the lower ends of the stops 58, the lower edge of the cone 83 will lie near the upper edge of a conical baflie I2 I, which is attached to the inner face of the inner shell I22 of the casing. -When the bell is in this completely raised position, the

baffle I2i and the crown cone I20 cooperate to streamline the atmospheric air as it flows in around the cup, and passes up into the duct 80. 1

The construction described andillustrated in connection with Fig. 4, and particularly the mounting for the spring, operates satisfactorily under ordinary Working conditions associated with a tank operating under a partial vacuum on its interior. However, under unusual conditions, it might happen that a sudden and considerable reduction in the pressure within the tank, would cause the bell to rise very suddenly, and in such a way that its head would impinge with considerable velocity against the lower ends. of

the stops 58. In case at specification required a construction to meet such a contingency, the same spring 82 that dampens or eases the lift of the bell to break the seal, can also operate to retard or cushion the upward movement of the bell toward the limit of its upward movement. This effect could be readily accomplished by attaching the upper end of the spring to the collar 05, and the lower end of the spring to the bushing 8?. With a spring mounted in that way, it will be evident that the spring could operate as a tension spring to exert a force on the bell to reduce its acceleration as it completed its upward travel.

Wherever the word pressure is used in this specification or in the claims, absolute pressure is referred to.

In connection with the operation of the spring 82, it should be stated that as soon as the bell has risen suiliciently to break the seal, or soon after that point, the spring will no longer be in compression. This prevents the spring from exerting a force after the seal is broken, that would give an acceleration to the upward movement of the bell.

Many other embodiments of the invention may be resorted to without departing from the spirit of the invention.

We claim as our invention:

1. In gas venting apparatus for relieving a variable pressure within a tank or the like, the

combination of a bell having a duct for receiving gas at the variable pressure, a valve-closure for the duct, the inner surface of which is exposed to the pressure Within the duct, for normally closing ofi flow through said duct; means for maintaining a liquid seal for the duct, and a liquid seal for the bell; said bell having a head carrying said valve-closure, and having an area exposed to the pressure Within the tank, and an area exposed to an external pressure, said bell operating to rise and break the ducts liquid seal at a predetermined difierential pressure between the variable pressure and the external pressure; all of said parts cooperating when said ducts liquid seal is broken to admit gas to the said duct from the interior of the tank, to flow past the valve closure; and a load picked up by the bell when it rises after breaking the said seal.

2. Venting apparatus for relieving pressure within a tank or the like, according to claim 1, said liquid seal means including a casing having an outer shell and an inner shell, and including a cup disposed centrally within .the inner shell for holding the liquid for the said liquid seal for the duct, means disposed on the axis of said duct for guiding the bell as it rises and descends, a substantially conical bafiie supported above said cup, and means for limiting the rising movement of the bell with the lower end of said duct located substantially adjacent to the upper edge of said bafile.

3. Venting apparatus for relieving pressure within a tank or the like, according to claim 1, said liquid seal means including a casing having an outer shell and an inner shell for holding a sealing liquid for establishing a permanent liquid seal for the lower end of the bell; and including a cup disposed centrally within the inner shell for carrying a liquid for the ducts liquid seal, and means disposed on the axis of said duct for guiding the bell as it rises and descends, including a guide stem secured in the bottom of said cup and extending upwardly therefrom into said duct.

4. In venting apparatus for maintaining a partial vacuum within a tank, above a minimum absolute pressure, the combination of a bell having a duct capable of communicating with the interior of the tank, a valve-closure for normally closing off flow through said duct, means for maintaining a liquid seal located between the valve-closure and the atmosphere, said bell having a head carrying said valve-closure substantially on the axis of the head, said head having an annular area on its inner side exposed to atmosphere; said bell operating to rise and break said liquid seal at a predetermined differential pressure between the interior of the tank and the outside atmospheric pressure; all of said parts cooperating when said liquid seal is broken, to admit atmospheric air to the interior of said duct, thereby enabling the force exerted by atmospheric pressure against the under side of said valve-closure, to assist the force exerted by atmospheric pressure upon said annular area, to lift and accelerate the bell when the liquid seal is broken; and a spring associated with the bell for exerting a lifting force upon the same before, and until the said inner liquid seal is broken.

5. In venting apparatus for controlling varying gas pressure within a tank or the like, the combination of a bell having a duct attached thereto carrying gas of varying pressure; means for guiding said bell to move bodily upward, a valve closure for the duct, the inner surface of which is exposed to the pressure within the duct, for normally closing off flow through said duct; means for maintaining a liquid seal for the lower end of said duct, said bell having a head with an area exposed to the varying pressure, and an area exposed to an external pressure, and operating to rise and break said liquid seal at a predetermined differential pressure between the said varying pressure and the external pressure; all of said parts cooperating when said liquid seal is broken, to permit the difierential pressure to open the valve closure so as to effect flow through the said duct, and a load picked up by the bell after it has risen for increasing the resistance to the upward movement of the bell brought into operation after it has broken the said liquid seal.

6. In a gas venting apparatus for relieving varying pressure conditions in a confined gas, the combination of a gas retaining bell confining a portion of said gas, means for guiding the bell for up and down movement along its own axis, means for maintaining a liquid seal at the lower end of the bell, said bell having a head at its upper end one face of which is exposed to a substantially constant pressure, and the other face of which is exposed to the varying gas pressure, a duct attached to the said head for effecting i0 communication for relief through the head between the space above the head and the space below the head, a valve-closure normally closing he upper end of said duct, means for maintaining a liquid seal at the lower end of said duct, located below the level of said first named seal, said bell operating when a sufficient differential pressure exists between the upper and lower faces of said head, to rise, break the seal for the duct and eiiect the opening of the valve to establish saidcommunication through the duct; and means for subjecting the bell to a damping resistance to its upward movement in addition to its own weight acting only after the liquid seal for theduct is broken, and the bell is moving in the first part of its upward travel, thereby damping the rising movement of the bell and the valve closure.

7. In a gas venting apparatus according to claim 6 forrelieving pressure within a tank, in which the means for resisting the movement of the bell includes a weight operatively associated with the bell so that after the bell rises, it lifts the said weight to increase the resistance to the upward travel of the bell.

8. In a gas venting apparatus for controlling the pressure within a tank or the like, according to claim 6, in which the means for damping the movement of the bell includes a weight having a lost-motion connection to the bell, so that the weight resists the rise of the bell after the same has broken the ducts liquid seal and the valve is opened sufiiciently to permit flow of gas through the same.

10. In a gas venting apparatus for controlling pressure within a tank, according to claim 6, in

which the tank operates under a partial vacuum within the same; and the means for damping the rise of the bell includes a spring, and means for mounting the spring so that the spring loads the bell and resists its rising movement when the bell duct has broken its seal and is rising.

11. In a gas venting apparatus for controlling pressure within a tank or the like, according to claim 6, in which the tank operates under a partial vacuum within the same; and the means for damping the rise of the bell includes a spring associated with the bell, and means for mountin the spring so that it functions to resist the lifting movement of the bell when the liquid seal for the duct is broken.

JOSEPH F. LEE.

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