US2371961A - Tank vent valve - Google Patents

Description

March 20, 1945.l

c. A.A ELLIS TANK VENT VALVE Filed Nov.'25, 1942 ||||I|| Il:

l inches of water.

Patented Mar. 20, h1945 kwarren STATES PATENT VOFFICE This invention is concerned with relief valves for the release of diierential pressures existing between the vapor space above volatile liquids stored in vapor tight tankage and the surrounding atmosphere. f

As is well known, gasoline, crude petroleum,

and similar volatile liquids or liquids containing volatile constituents are normally stored in tanks with vapor tightl roofs capable of withstanding pressurel and vacuum ranging from a fraction of an inch of water pressure to several inches of water pressure to avoid evaporation losses. At the same time, due to expansion and contraction of theicontents of the vapor space due to temperature changes, and also to pumping in or removing liquid, it becomes necessary to provide for egress or ingress of considerablevolumes of vapor or air. Tank vent valves are used to accomplish this purpose, l

This invention has for its object the provision of a liquid sealed vent Valve for this purpose which valve does notA force .passage ofy vented vapors or incoming airl through 'the sealing liquid. It has also the object of providingsuch a valve capable of passing vquickly from closed to full capacity position. i

y The construction of my novel valve will be understood by reference to the drawing attached hereto the figure of which shows a vertical, section through the valve.

In the gure, I is the external shell of the valve, closed at the top byplate I I, and equipped near its upper end with ports I2 of suicient area to vent the maximumy outward gas flow which Athe valve is expected to handle. The cover plate II may be extended and anged downwardly, as at I3 to protect the ports from ingress of rain, dirt, and the like. The valve is mounted upon and supported by a central pipe I4 which communicates with the vapor'space of the tankuto be protected. within valve body lo and aroundy and over pipe I4 there is a valve member I5 composed of a skirt I6 and cover plate I'I.` This valve member is so constructed that its total weight, divided by the area of the underside of plate I 'I which lies within the skirt I6, is that design pressure at which the tank must be vented. This pressure will normally be about 1 to 4 The valve member I5 is so mounted that its skirt I6, which is spaced inwardly from wall I0, as at I 8, dips into and is sealed by liquid I9. This liquid may be water, glycerine, mercury, or any of the .liquids usually usedfor this purpose. I normally prefer water,- and when it is desired that the valve b e kept in service during freezing weather, brine. The submergence of v Y the skirt I6 in liquid I9 is so calculated that any tank pressureless than sucient to lift valve member I5 will not be bypassed under skirt I6. That is, as the pressure in the tank rises the sealing liquid rises within space I8, reaching a level '20 when the pressure reaches design relief pressure level. At that instant valve member I5 lifts, andthe liquid drops away. The length of dip skirt I6 and the distance between the bottom of orices I2 vandithe bottom of the valve body is` such that when the dip skirt I6 leaves the sealing liquid, the outward flange 2| of Valve body cover plate I'I is still below the bottom of ports I2, so that the liquid is permitted to drop away without any more blowing through the liquid. than just enough to transmit tank pressure into passage 20. At this instant the pressure Within thetank commences to act, not' only upon thev bottom area of plate I1 within skirt I6, but also upon the bottoni area of the overhangingoutward ange 2l, giving a' force substantially greater than just necessary to lift the valve member, andthe valve rises to the position indicated by dotted lines, above or-ilces I2 and vents. As, long as it is venting, the lifting pressure works upon both areas, and consequently the valve willnot drop and close until the tank pressure is at a level below that at which the valve was opened.

, This gives a snap return, at a rpressure at which no vented gas will pass through sealing liquid I9.

fromplate 22 by edge-mounted'radial members 26. This structure is so proportioned that the entire weight of the member, divided by. the area of the underside of plate 22 between skirts 23 and 24 is equal to the design vacuum venting pressure. Access of atmosphere to the underside of plate 22 is by annular port 21; formed in the valve body by ring plates 28 and 29. Since the vacuum vent pressure level is lower than the internal pressure vent pressure level, skirt 23 will be shortery than the skirt I6 of the pressure valve member I5, and when the vacuum vent valve assembly is lifted, it' will be stopped by and Within pressure vent valve I5 in the position shown by the dotted By these means I have completely avoided any blowing through sealing liquid, while lines, at which time atmospheric air flowing in through passage 21 will flow freely through the space around the now elevated skirt 23, through the space between plates 22 and 25 in their elevated position, and through pipe I4 into the tank. Also, when the skirt 23 is lifted from the sealing liquid, plate 25 has not yet passed `above the end of pipe I4, and at this instant, the inowing air will exert lifting pressure against the underside of plate 2.5, which is a larger area than that of plate 22, `thus giving vthe same snap action for opening and closing and the same avoidance of blowing through theliquid seal as in the pressure.` :f relief valve assembly. It is equally clear that the. motion of this valve from full closed to full open position will be practically instantaneous, the' sealing liquid around skirt 23 acting n the same manner as that described for that around skirt' venting, skirt 24 is made longer than is skirt 23, and its sea-1 well 3U is correspondingly deepened.l To permit maintenance of liquid in this seal, one or more bridge passages for liquid across'annula'r port 21 are provided, as at 3I. `'lo support theA whole assembly with respect to pipe i4 and pre'- serve its alignment, several Vbracketsl 3 2, usually. three equally-spaced brackets, are provided. An optional faturevwhich is of real merit is utilized to maintainthe seal liquid level over long periods' without inspection, as follows: the cover plate II of the main valve body may be extended upwardly as at 33 to provide an auxiliary seal liquid` container, closed by a plug 34. Downwardly into the valve, through plate II, and extending into the sealing liquid to the plane of normal level of liquid attained in space I8 just lbefore vacuum venting, there extends a pipe 35. Thus, when the seal liquid becomes depleted, as by leakage or evaporation, additional liquid will be fed in at these times, and the proper volume of liquid auto-v matically `maintained within the valve.

The Whole assembly is simple in character, formed of flats and simple tubular shapes, and is most conveniently and cheaply assembled by welding. Since cover plate II is removable, complete and ready 'access may be had to the entire interior by removalof the moving valve members and complete cleaning or necessary maintenance is facilitated. i

I claim:

1*. In a tank vacuum relief val-ve of the kind described a casing having vertical side walls and towallof said casing except.` for sufcientclearance to permit vertical movement andan orice with similar clearance for passage of said centralpipe, said secondary plate similarly clearing said central pipe and being ofsubstantially less area than said top plate, said dip skirt depending from the outer edge of said secondary plate, means to admit atmospheric pressure to the underside of said secondary plate Within said dip skirt, the

. area so exposed being sufficient to lift the valve when exposed to design vacuum relief pressure, the depth of the sealing liquid, the Vlength of the dip skirt, the space between the two plates and the height of the central pipe being such that the dip skirt is pulled from the sealing liquid y.before the top plate passes above the end of the 'central pipe, at which moment the atmospheric pressure Vhas `access to the underside of the top plate to lift the valve to venting position and to prevent closing of the valve until the vacuum is I6. To prevent blowby along pipe I4 on vacuum? 3' reduced to a vacuum substantially below the design vacuum relief pressure.

f2. In a combined ypressure and vacuum relief valve for use' upon storage tanks handing volatile liquids, a casing having substantially vertical walls, a top closure, a bottom closure, and a vcentral pipe adapted to communicate with a tank to be vented, orifices in said casing near the top thereof, a sealing liquid in said casing, a gasometer type pressure relief valve Within said casing', said pressure valve comprising atop plate and a dip skirt, said top plate extending from Wall to Wall of v'said casing except for clearance sufficient to permit vertical movement, said dip skirt being spaced away from the Walls of said casing and Y defining a lift area upon the underside of said top plate sufficientV for lifting the valve at design' relief pressure, the -submergence of the dip skirt and the location of the orifices inthe casing being such that the valve must Amake substantial lvertiv cal travel after the dip skirt leaves the sealing liquid before the top plate clears the orifices and permits free venting, a vacuum valve comprising a top plate and a dip skirt within said pressure 'valve and surrounding said central pipe, means to admit atmospheric air into the space Within the pressure valve at a point under the vacuum valve top plate and above the scaling liquid, the vacuum valve top plate extending fromwall to wall Within the pressure valve dip skirt which acts as a casing therefor except for cearance sufcient to permit vertical motion and 4having an oriiice Withsimilar clearance for the centra-l pipe, the vacuum valve dip skirt being spaced away from the central pipe to permit access of design vaci uum vent pressure to a limited lifting area suincient to lift said valve so long as the vacuum valve isseated, the length of the vacuum valve dip skirt and the height of the point of access to the cen` tral pipe being so proportioned as to require additional travelafter -the vacuum valve dip skirtl has left the sealing liquid before `free venting is permitted. y j

' CLIFFORD A. ELLIS, j j

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