Fluid handling – With indicator – register – recorder – alarm or inspection means – Position or extent of motion indicator
Reexamination Certificate
2000-07-11
2001-08-21
Chambers, A. Michael (Department: 3753)
Fluid handling
With indicator, register, recorder, alarm or inspection means
Position or extent of motion indicator
C251S056000, C137S556000, C074S424830
Reexamination Certificate
active
06276394
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of plug valves and more particularly to the field of non-lubricated double block and bleed plug valves.
2. Background Art
The Twin Seal double block and bleed plug valve uses a “retract before turning to open motion” which displays both ¼ turn rotary and linear movement with multi-turn input. This is presently accomplished by valve operators comprising a two piece stem set which when properly coordinated with the housing, will produce linear travel when the outer stem and housing are locked with the roller preventing rotary motion and allowing only linear motion while the input rotates. Similarly, at the extreme top of the motion of the outer stem, the roller is allowed to move inwardly (radially) locking the inner and outer stem together for only rotary motion (¼ turn only).
There are presently six basic functions being performed in these operators.
1) INPUT—rotary handwheel or motor input—provides turn force;
2) “L” SLOT—prevents operator from overtravel/undertravel/premature travel/improper travel;
3) TRANSLATION—forces rotary or linear travel;
4) THREADS—provides linear force;
5) INDICATOR—provides visual indication of plug position at the top of the operator;
6) PLUG CONNECTION—connects the operator to the plug.
Such prior art deploys these six functions in numerous discrete locations as can be seen in patented prior art designs. Attempts were made in the prior art to “compact” the stem sets by combining the input and threaded sections. Also a rotary translation device was implemented to assist in minimizing stem length, but this device only allowed for one revolution of the stem (¼ for turn ¾ for lift) which limited use to high-pitched stems. Also the stem doubled as the indicator shaft. This reduced the six functions to four discrete locations.
The problem with stem sets having numerous discrete and separate locations for accomplishing the listed six functions, is length. Long operators are inherently more susceptible to damage, less convenient for positioning valves in tight spaces, susceptible to instability and warpage and not conducive to casting with higher strength materials. Moreover, fabrication tends to be more labor intensive thus contributing to a higher price valve.
It would be highly advantageous if it were possible to provide a stem set configuration which significantly reduced the length of the valve operator.
SUMMARY OF THE INVENTION
The present invention provides a radical improvement in the stem set configuration for a double block and bleed plug valve. The improvement provides an operator which can be significantly shorter and more compact than conventional operators for such valves.
The invention makes use of a novel nesting of the threading section whereby a conventional female thread is replaced by a nested male thread surrounded by the translation section. The translation section, in turn, houses the indication section inboard of the nested male threads thereby compacting three functions into one location. This design lends itself nicely to investment casting technology obviating conventional machine shop practices. The invention also combines by use of a long plug stem pin, the plug connection and L slot functions into one location. The input function still remains separate, however, combining ultimately all functions in only three discrete locations and what appears at this time to be the ultimate compacted or nested arrangement.
By turning the handwheel, the input shaft of the inner stem is rotated in accordance with the direction of the handwheel whose torque is transmitted via a key. This input shaft is allowed by virtue of its collar and the housing and retainer plate, rotary motion only (no linear motion).
When roller apertures are in rotary alignment with the roller tracks and the input shaft rotates, by virtue of its male threads it causes the output shaft to travel linearly up and down (handwheel rotates cw down, ccw up). When the roller apertures are in rotary and vertical alignment with the inner stem recesses, the input shaft and outer stem rotate as one unit by virtue of the three rollers “locking” the shafts together.
At the transition of linear to rotary motion, the rollers move from the housing track/outer stem to the outer stem/inner stem. The rollers are configured so that only one position can be supported at the exact corner of the L-slot. However, the rollers require guidance which is the function of the L slot pin.
The advantages of the present invention may be summarized as follows: It is more compact than previous designs; it fits in tighter spots; it allows for more room on walkways and for maintenance; the compact design allows for high strength materials of construction which, in turn, allow the operator to be directly driven without gears and their associated bulk and costs; the compact design reduces weight and mass. High strength materials allow a smaller operator to work at more demanding loads; the compact design and improved harder cast materials extend operator life; the compact design and improved harder cast materials allow for maintenance free operation (w/perm lube); the compact size allows for investment cast technology since warpage/stability is not an issue as in large and especially longer castings; the high strength, high wear resistant, thermally stable material preferably used in the invention needs compact designs to be practical; the compact dimensions allow for extra pull off without adding length.
Another significant feature of the present invention resides in the novel use of at least three symmetrically located rollers in the stem set assembly. Three rollers at 120 degree intervals provide a balanced force arrangement which reduces wear and increases reliability.
OBJECTS OF THE INVENTION
It is therefore a principal object of the present invention to provide a more compact operator apparatus for use with double block and bleed plug valves.
It is another object of the invention to provide a foreshortened stem set for a plug valve operator by employing a nested male thread in a translatable outer stem for receiving a rotatable inner stem.
It is yet another object of the invention to provide a plug valve operator apparatus which is designed to be sufficiently compact in length to permit manufacture by casting of extremely hard materials to virtual net shape.
It is still another object of the invention to provide a balanced force, symmetrical roller assembly in a stem set operator for a double block and bleed plug valve.
REFERENCES:
patent: 3046802 (1962-07-01), Cupedo
patent: 4195816 (1980-04-01), Thompson et al.
patent: 4234157 (1980-11-01), Hodgeman et al.
patent: 4235258 (1980-11-01), Uno
patent: 4350322 (1982-09-01), Mueller
patent: 468270 (1946-08-01), None
Lilie Kevin W.
Smith Gordon M.
Chambers A. Michael
General Valve, Inc.
Tachner Leonard
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