US2517194A - Vapor pressure relief system - Google Patents

Description

Au 1, 1950 o. GARRETSON VAPOR PRESSURE RELIEF SYS'I'EI Filed lay 27, 1946 INVENTOR.

O. L. GARRETSON ATTORNEYS 2 Patented Aug. 1, 1950 VAPOR PRESSURE RELIEF SYSTEM Owen L. Gar-retina, Bartleeville, rhilllpa Petroleum Company, Delaware Okla llllgnor to a corporation of Application Ray 27, 1948, Serial No. 672.600 1 Claim. (Cl. l37-53) This invention relates to vapor pressure relief systems. In one specific aspect it relates to vapor pressure relief systems for tanks containing a liquid of high vapor pressure in which the vapor pressure relief system is designed to preferentially draw vapor rather than liquid from the tank. In another specific aspect, it relates to vapor pressure relief systems for tanks mounted on vehicles, which vehicles may be upset or overturned, but in which the vapor pressure relief system will still preferentially discharge vapor rather than liquid.

Liquids of high vapor pressure are often transported in vehicles. Such vehicles are generally tank trucks and the liquid of high vapor pressure is often propane or butane or mixtures of the same or other hydrocarbons of similar boiling point. Such tanks are provided with relief valves so that when the pressure dllferential across the relief valve exceeds a predetermined amount, the relief valve will open and allow discharge of fluid so that the tank will not burst. Due to such relief valves there has been a minimum of danger connected with the transport of such liquefied petroleum gases.

However, in a few instances the tank truck has been involved in an accident with the result that the truck is displaced from an upright position. In the prior art, this has resulted in the relief valve being connected to the liquid in the tank instead of the vapor space above the liquid. As long as no fire occurs and the relief valve stays closed, there is no difliculty. In a few instances, there have been fires which have raised the vapor pressure inside the tank. The relief valve being connected to the liquid, because of the upset position of the tank truck. the pressure generated by the fire is relieved by the venting of liquid petroleum gas. The relief of liquid is not efficient in relieving vapor pressure above the liquid and the quantity of fuel discharged is greatly increased because liquid is discharged. The liquid fuel discharged vaporizes and becomes ignited by the fire in most instances in which case the fire already existing is greatly increased. which in turn raises the pressure and vents all the liquid.

The present invention provides means whereby the relief valve will only discharge vapor regardless of whether the tank truck is upside down or not. Regardless of the truck position. both the liquid and the counterweight on the pivoted inlet stack are in the lower region of the tank with the result that the relief valve can never discharge anything but vapor. or at least the discharge of liquid through said relief valve is minimized.

. One object of my invention is to provide an improved vapor relief system for tanks containing liquids of high vapor pressure.

any discharge of liquid through such a vapor pressure relief system is minimized.

Another object is to provide automatic means for venting vapor and minimizing the discharge of liquid from a tank regardless of the position in which the tank is disposed.

Another object is to provide a foolproof, simple and eillcient instrumentality for carrying out the above objects.

Numerous other objects and advantages will be apparent to those skilled in the art upon reading the accompanying specification, drawings and claim.

In the drawing:

Figure 1 is an elevational view of a liquid petroleum gas tank truck embodying the present invention.

Figure 2 is an enlarged cross sectional view, with parts broken away, of a portion of Figure 1 showing in detail the vapor pressure relief system.

In Figure 1, an automotive truck or other vehicle 3 is provided with a tank 4 for containing liquid petroleum gas. Tank 4 may [be secured to truck 3 by any suitable means such as bands 5. Tank 4 is provided with relief valve means for discharging fluid under excessive pressure to the atmosphere through stack 6. The outlet end of stack 6 may be closed by an easily removable rain cap I. The relief valve means is not shown in Figure 1, but will be described fully with reference to Figure 2.

In Figure 1, stack 6 and rain cap I are not absolutely essential as the fluid under excess pressure could be discharged from pipe I. It is preferred to attach elbow 8 and stack 6, however, in order to direct the vapors upwardly to reduce chances of their ignition. Rain cap I is easily blown out of pipe i by fluid pressure when the relief of pressure occurs.

In Figure 2, tank 4 may be provided with an opening or man hole Ill and man hole It may be covered by a man hole cover ll secured to tank 4 by bolts I2 or other suitable means. In some aspects of the invention, however, the details of construction as to whether certain parts are integral or separable or whether they detach at some point or another do not form any part of the invention as alternative construction will obviously operate in the same manner.

Man hole cover II has a relief valve opening 13 therethrough and secured to man hole It by welding I4 is the inlet end I! of a relief conduit. The relief conduit also comprises pipe 8, elbow 9 and stack i if desired, although parts i, I, I and 9 may be eliminated if desired.

Pipe I5 is secured in communication with opening l3 and pipe It has an anti-iriction-bearing swivel-Joint Ii mounted thereon. Because any Another object is to provide means whereby .0 suitable type of swivel-Joint may be used at this 3 point, no details of construction are shown. Any usual ball bearing swivel-joint is preferred.

Rotatably mounted to swivel on swivel-joint I6 is a counterweighted stack generally designated as H. Stack I1 may consist of T l8, pipe 19, pipe 20, stack 2| (this having inlet opening 22 at its upper end) and counterweight 23 is secured by welding 24 to pipe 20. Counterweight 23 may contain lead 25 or suitable weighting material if necessary, depending on the ease with which swivel 16 operates.

Any of the usual types of relief valves may be inserted at any point in the relief conduits 2|, l1, l9, I6, l5, II, 8, 9, or 6, but it is preferable to place the relief valve so that it is relatively accessible and yet not likely to be sheared off or otherwise removed from the tank 4.

Therefore, I have located the relief valve generally designated as 26 at the point shown. Relief valve 26 has a flange 21 on the exterior of its body '28 and this flange is secured to man hole cover H by means of collar 29 and bolts or other suitable fastening means 30.

Body 28 has a passage connecting the space inside pipe l to that inside pipe 3, and valve 26 has a valve head 3| normally urged to closed position to close the passage in body 28 by spring 32 acting on valve stem 33. Valve stem 33 is connected with valve head 3 I. Valve head 3| may be provided with an eye 34 which eye is used in testing the relief valve. One form of construction which may be used for the connection between spring 32 and valve stem 33 is the use of collar 35 and lock nuts 36 and 31.

Operation The operation of the deviceis self evident. Should reckless drivers in other vehicles force the driver of vehicle 3 off the highway into a ditch so that tank 4 is in an overturned position, and should the pressure in tank 4 (because of fire or for other reasons) become great enough to open relief valve 26, the relief valve 26 will vent vapor to the atmosphere, because stack 22 will have been rotated up into the vapor space above the liquid due to the action of the force of gravity on counter weight '25, as swivel 16 will allow such rotation.

The axis of rotation of swivel I6 is preferably parallel to the longitudinal axis of truck 3 and, because of the relatively long wheel base of truck 3, a swivel is sufficient at [6. If desired, swivel l6 may be replaced by a suitable universal joint but, because of mechanical difliculties, a simple swivel I6 is preferable. Swivel-joint I6 is preferably packed in the conventional manner to prevent any substantial amount of liquid from leaking from the tank into the relief conduit.

While I have shown in the drawing, a particular illustrative form of my invention, various modifications may be made in the same and in the various features of construction, without materially changing the invention therein, and formal changes may be made in the specific embodiment of the invention described without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claim.

Having described my invention, I claim:

"In a tank for high vapor pressure fluids, the improvement of a pressure relief device, comprising in combination a, single outlet conduit extending centrally through and rigidly affixed in a side wall of said tank; a swivel flexibly attached and supported by the inner end of said conduit and forming a passage therebetween; a stack rigidly attached to said swivel, communieating therewith, and extending upwardly therefrom to a point above the normal liquid level in REFERENCES CITED The following references are of record in the file of this patent: V

UNITED STATES PATENTS Number Name Date 223,396 Shabley Jan. 6, 1880 1,365,567 Thomson Jan. 11, 1921 2,183,034 Voit Dec. 12, 1939 2,364,119 Anderson Dec. 5, 1944

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