Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-03-21
2003-03-04
Trieu, Van (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S624000, C220S216000, C220S220000
Reexamination Certificate
active
06529134
ABSTRACT:
TECHNICAL FIELD
The invention concerns a device and method for remotely selectively securing a floating tank roof in a desired position.
BACKGROUND OF THE INVENTION
Above ground storage tanks are frequently used to store hydrocarbon liquids. When the stored liquid is volatile, the storage tank is usually equipped with a floating roof, which floats on top of the stored liquid and moves up and down with the liquid level. Floating roofs greatly reduce liquid evaporation, preventing loss of the stored liquid and reducing pollution due to hydrocarbon evaporation into the atmosphere.
Such floating roofs are generally provided with support legs which are usually spaced about twenty feet apart and provide support to the roof when the roof is not floating on stored liquid, such as when the tank is emptied or taken out of service for maintenance. It is desirable for the roof to be allowed to drop to within about three feet of the floor during product storage. However, if it is necessary for personnel to enter an empty tank, three feet of clearance between the roof and the floor is insufficient.
Accordingly, floating roof support leg assemblies often comprise a sleeve which penetrates the roof and is securely attached thereto, and which provides a longitudinal cavity. Such support leg assemblies also comprise a sliding leg which slides through the longitudinal cavity of the sleeve. The sleeve extends about three feet, or the minimum desired landing height of the roof, below the bottom surface of the roof. The roof can be landed on, and supported by, the sleeves if the lower landing position is desired. In this configuration, the sliding legs are allowed to slide freely upward through the longitudinal cavities of the sleeves and do not interfere with the downward positioning of the roof.
As the roof floats upward, the sliding legs slide downward through the longitudinal cavities of the sleeves. If the sliding legs are sufficiently short, and the tank sufficiently tall, the roof could float to a position from which the sliding legs would fall out of the sleeves. Accordingly, the sliding legs can be provided with a cap or another stoppage device, such as pins, which prevent the tops of the sliding legs from sliding downward through the sleeves.
Positioning holes cut through both the sleeves and the sliding legs can be set so that they are aligned when the sliding legs extend below the base of the roof a desired distance, such as six feet, or some other height sufficient to allow personnel access into the tank. With the roof floating at approximately the desired height above the storage tank floor, and with the positioning holes in the sleeves and the sliding legs aligned, the sliding legs can be locked into position relative to the sleeves by inserting locking pins essentially horizontally through the aligned holes. Thus, as the storage tank is emptied and the roof lowers, it will be landed in a high roof position on the bases of the sliding legs at the desired height above the storage tank floor.
Current systems which provide this type of floating roof height adjustment require that the locking pins be set by hand. This requirement results in labor costs which must be incurred every time the high roof position must be obtained over an empty storage tank. Further, governmental safety regulations often preclude allowing workers onto a floating roof when the storage tank is in service, so that setting up the roof to obtain the high roof position requires: (1) emptying the tank and landing the roof on the sleeves (the low roof position); (2) refilling the tank with water until the positioning holes in the sleeves and the sliding legs are aligned; (3) manually setting the locking pins; (4) emptying the tank a second time, landing the roof on the sliding legs (the high roof position); (5) performing the necessary work inside the tank; (6) refilling the tank with water again to float the roof; (7) manually removing the locking pins; (8) emptying the water from the tank; and (9) refilling the tank with stored product.
Even if the tank is filled with water during the manual setting and removal of the locking pins, safety regulations may require that personnel on the tank roof be provided with breathing apparatus, which increases the expense of such an operation and requires larger crews to provide the specialized services required.
Accordingly, it is desirable to provide a device which can set and remove locking pins under remote control, and without requiring the repeated and expensive process of draining the tank and refilling it with water to allow the roof height to be set.
BRIEF DISCLOSURE OF THE INVENTION
The invention provides a locking pin setting mechanism for a storage tank floating roof which is remotely actuatable, and which will reliably allow the floating roof to be positioned for a landing on its sliding legs as opposed to its sleeves. The invention comprises a plurality of pneumatic cylinders, each of which is securely attached to, or securely positioned relative to, one of the sleeves. Each pneumatic cylinder controls the essentially horizontal position of a locking pin, and is positioned relative to its respective sleeve so that actuation of the pneumatic cylinder will move the locking pin into, or out of, a positioning hole cut essentially horizontally through the sleeve.
The invention also comprises a plurality of sliding legs, each of which also comprises a positioning hole cut essentially horizontally through it. The sliding legs are inserted through the longitudinal cavities in the sleeves so that, when the positioning holes in the sleeves are aligned with the positioning holes in the sliding legs and the locking pins are inserted through these holes, the floating roof may be landed on the sliding legs and securely maintained at a height sufficiently above the tank floor so that personnel can safely enter the tank. After the personnel exit the tank and the tank is refilled, the pneumatic cylinders may be remotely actuated to withdraw the locking pins and again allow the floating roof to obtain its full vertical range of motion.
Because it is desirable to be able to set the locking pins without emptying the stored liquid from the tank, or to withdraw the locking pins with the stored liquid, rather than water, in the tank, the preferred embodiment of the invention uses spark-free pneumatic cylinders to position the locking pins. As those of skill in the art will recognize, other actuating devices, such as mechanical, electro-mechanical, or electrical devices may be used to position the locking pins. However, such devices may create sparks through either electrical discharge or mechanical friction, thereby presenting a safety hazard.
Each sliding leg of the preferred embodiment also comprises an essentially cylindrical sleeve positioned essentially horizontally through the sliding leg and aligned with the sliding leg positioning holes. This essentially horizontal sleeve assists in guiding the locking pin during the insertion of the locking pin through the positioning holes in the sleeve and the sliding leg. Preferably, the sleeve is secured in position relative to the sliding leg positioning holes by welding the sleeve to the sliding leg at both ends of the sleeve. However, the sleeve can also be supported internal to the sliding leg by providing horizontal or vertical supports which are in turn secured to the sliding leg. Further, in the preferred embodiment, each locking pin comprises a tapered end which is the lead end of the locking pin during the process of inserting the locking pin through the positioning holes in the sleeve and the sliding leg. Such a tapered end aids in preventing mis-alignment of the locking pin with the positioning holes and thereby decreases the likelihood of jamming the locking pin.
It is also part of the preferred embodiment to provide a visual indicator, for example, reflective paint, on the portion of the locking pin at and near the tapered end. Such a visual indicator allows someone above and outside of the storage tank to visually verify that t
Hirschbuehler John F.
Machen Joel L.
HMT Inc.
McConnell R. Perry
Trieu Van
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