Fluid handling – Liquid level responsive or maintaining systems – With second diverse control
Reexamination Certificate
1999-07-28
2001-09-25
Walton, George L. (Department: 3753)
Fluid handling
Liquid level responsive or maintaining systems
With second diverse control
C137S442000, C137S446000, C141S198000
Reexamination Certificate
active
06293302
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a valve assembly and, more particularly, to a valve assembly for a tank that prevents filling of the tank beyond a predetermined maximum fill level.
BACKGROUND OF THE INVENTION
There have been a number of different valve assemblies designed to prevent the fluid level in tanks from exceeding a predetermined level of fluid therein. In particular, with a tank used to contain compressed or liquified gas, such as propane, it is important that the liquified gas loaded into the tank under pressure not exceed a certain fluid level in the tank so that a sufficient amount of head space at the top of the tank is maintained for safety purposes. Because of the high coefficient of thermal expansion of liquified propane gas, increases in ambient temperatures can cause the head space in the tank to be rapidly consumed. The tanks are rated so as to withstand a predetermined amount of internal pressure; however, if the tank is overfilled beyond the maximum level, there is the danger that the internal pressure may exceed the rated strength of the tank, particularly if exposed to excessive temperatures, and lead to potentially dangerous failures of the tank walls, and/or lead to dangerous expulsion of gas or liquid from a relief valve.
In this regard, it is known to provide the tanks with a dip tube that extends through the tank wall into the tank interior space to a specified level below the maximum fill level with its other end open to ambient so that once the fluid level reaches the bottom end of the tube, the liquified gas begins to be evacuated from the tank. As is apparent, if the operator who is filling the tank does not detect this condition and continues to fill the tank, a potentially hazardous situation around the tank filling station is created.
As mentioned, there have been a number of prior art devices that prevent further filling of the tank once the maximum fill level is attained. One of the problems with some of these prior valve devices is that they are not readily adapted for use with current service valves that are already in place on the tanks. In this regard, many of these valves do not allow for outgoing flow therethrough or, if they do so, only allow such reverse flow in relatively small amounts. Another shortcoming with a majority of these devices lies in their complexity, as many require a large number of different parts. For example, in a number of prior art patents, the valves utilize a primary valve member and a secondary valve member controlled by a float assembly. The primary valve blocks incoming fluid flow when the float assembly is operable at maximum fill conditions to seat the secondary valve. When the secondary valve seals its associated port, there is a fluid pressure buildup between the secondary and primary valves that pushes the primary valve onto its seat sealing lateral ports to stop fluid flow into the tank. The use of two moving valve members, and the large number of associated parts in such a valve assembly, is undesirable in terms of driving up the cost for the valve, increased time and complexity for assembly thereof, the greater likelihood of its failure under repeated cycling over time, and the ability to provide for adequate outgoing flow therethrough.
Another problem with prior valve devices is that they have trouble providing precise and repeatable fluid flow cutoff during tank loading operations once the maximum fill level in the tank is obtained. Pertinent regulations specify that a predetermined amount of head space remain above the maximum fluid level for safety purposes, as mentioned. However, with prior valve devices, the point at which they cut-off fluid intake into the tank during loading operations can vary in terms of the fluid level in the tank from the predetermined maximum fill level by as much as 1½ percent.
Accordingly, there is a need for a simpler and less expensive valve assembly that prevents overfilling of tanks beyond a predetermined fluid level therein. More particularly, it would be desirable to provide an overflow protection valve assembly that can be attached to a service valve such as on an LP tank for allowing flow into and out from the tank through the valve assembly. A valve assembly that provides more precise fluid flow cut-off at the predetermined maximum fill level would also be desirable.
SUMMARY OF THE INVENTION
In accordance with the present invention, a valve assembly is provided which stops fluid flow into a vessel at a predetermined fluid level therein, while allowing good fluid flow therethrough for filling the vessel and for discharging fluid therefrom. The preferred form of the valve assembly is for use with an LP tank for containing liquified propane gas. Thus, when the term fluid or fluid flow is utilized herein, it will be understood to encompass both the flow of compressed or pressurized gas (e.g., propane) in a fluid state, and the flow of propane in its gaseous state and combinations thereof where the liquified gas is undergoing two-phase flow depending on the relative pressures in the tank versus the pressurized filling source and/or the ambient.
The valve assembly of the present invention includes a valve member which shifts in a valve housing as controlled by the rising and falling of a float assembly as the fluid level in the vessel rises and falls. The valve member shifts into a blocking position relative to a port of the housing that communicates with the vessel interior at a predetermined maximum fill level in the vessel interior space. A fluid flow path is provided through the housing with the valve member blocking position being between the flow path and the port of the housing. When the fluid level in the vessel is below the maximum fill level, the float assembly shifts the valve member from the blocking position and keeps it removed from the flow of fluid between the flow path and the port. In this manner, the valve member is not exposed to fluid flow in the housing during filling operations of the vessel. Because the valve member is removed from the fluid flow, a substantially unrestricted flow path is provided through the valve assembly herein so as to provide a sufficiently high rate of flow into the vessel for rapid filling of the vessel such as to the maximum fill level, if desired.
In one form, the valve housing includes a seat at the port and the valve member shifts onto the seat in the blocking position at the predetermined maximum fill level with the incoming fluid flow during filling operations assisting in tightly pushing the valve member onto the seat to prevent flow through the port and into the vessel interior. Thus, while the present valve assembly keeps the valve member removed from the fluid flow during filling operations at fluid levels below the maximum fill level, the valve assembly is designed to makes use of the flow in obtaining a tight seal to prevent further flow into the vessel interior once the maximum fill level is attained.
The valve housing may include an inner member in which the valve member shifts and an outer member rigidly attached to the inner member with the flow path defined between the housing inner and outer members. The flow path can include a plurality of discrete flow paths around the housing inner member for redirecting incoming fluid around the valve member in the inner member. Each of the flow paths communicate with the port of the housing for directing incoming fluid therethrough during vessel filling operations and for receiving outgoing fluid through the port from the vessel interior during vessel unloading operations.
In another form, the flow path has a predetermined size for permitting a predetermined flow rate of fluid therethrough during filling operations to limit fluid turbulence that would keep the valve member from shifting to the blocking position at the predetermined fill level. Keeping the valve member removed from the flow of fluid through the valve assembly during filling operations allows for a good flow rate of fluid into the vessel, as previously discussed. It is also
Waters Michael
Yet Chan
Fitch Even Tabin & Flannery
Walton George L.
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