Fluid handling – With leakage or drip collecting
Reexamination Certificate
2000-04-24
2001-11-27
Lee, Kevin (Department: 3753)
Fluid handling
With leakage or drip collecting
C251S331000
Reexamination Certificate
active
06321776
ABSTRACT:
FIELD OF INVENTION
The present invention relates to fluid control devices and in particular to those applications where materials of construction must be compatible with the process fluids and where it is a requirement that minimal volumes of fluids are captured within the valve. Often times the only suitable material meeting these requirements will be PTFE or other Teflon types. Furthermore, these applications often require that no cracks or crevices are present to permanently capture fluids or particulate carried by the fluid. Another requirement where slurries are being controlled is that the fluid should not be subjected to high rates of shear. Lastly, these fluids are often highly toxic and a double containment is necessary for any thin walled barrier in contact with the fluid.
BACKGROUND OF INVENTION
Many forms of throttling valve are found within the field. Viraraghavan describes a valve in patent '530(cited in the references) that that is typical of valves that may, at first, may be deemed to be satisfactory for these applications. However, as is typical in many valve designs the stem must be sealed with o-rings. This introduces both small cracks and crevasses, as well as another material(the o-ring) that may not be compatible with the process fluid. These problems can be solved with diaphragm valves. Linder, in patent '086(sited in the references) describes one such approach. Here a metallic actuation shaft is buried in the flexible diaphragm such that it is susceptible to corrosion from ionic migration from some process fluids. Secondly, this valve contains a large number of parts of metallic content as well as a comparative large volume of fluid should the primary diaphragm fail. Generally valve designs described in the art attack one or two of the problems described, but none approach the whole problem of safely handling highly toxic or corrosive fluids while providing a smooth continues laminar flow in a free draining, low captive volume device.
The throttling mechanisms described in the art contain sharp corners and short flow paths to control the flow. Many fluids are both hazardous and suffer detrimental effects to sheer effects when flowing around such obstructions. The slurries used in the semiconductor industry are known for their sensitivity to shear. It is generally known in fluid mechanics, that laminar flow is achieved for Reynolds numbers of less then 2000. Where the Reynolds number is computed as follows:
Re=Dv&rgr;/&mgr;
e
Where D is the height of the flow channel, v the fluid velocity, &rgr;the density, and &mgr;
e
the fluid viscosity. Furthermore, the pressure drop, &Dgr;P, along the channel is expressed differently for laminar flow that for turbulent flow which occurs and higher Reynolds numbers.
For Laminar flow: &Dgr;P=K(&mgr;Lv/D
2
)
For turbulent flow: &Dgr;P=K′(UD)(v
2
)
Where K and K′ are constants of proportionality that depend on the engineering units selected. It can be clearly seen that the pressure drop, hence, the throttling effect on the flow stream is a linear relationship to the fluid velocity for laminar flow and a velocity squared relationship for the turbulent flow case. Obviously the ideal case is a linear relationship of pressure loss to flow velocity across the throttling range. A less desirable situation is the square law response where the response of the valve continuously varies over the throttling range. Any configuration that results in the flow response being linear over a portion of the range and transitioning to square law at some point will have a detrimental effect on the ability of the controller to smoothly regulate the flow. In additions since both relationships contain the length factor L in the numerator it is desired to have some length to the throttling path.
In order to provide a throttling effect it is necessary to control the opening of the fluid channel. Many means are described in the art. These are typically motors, solenoids, compressed air, or manual adjustment devices. The applications envisioned herein all contain a flow meter to measure the flow and advanced electronics to position the valve to achieved the desired mass or volumetric flow rate. Thus, the position of the valve is not so much of interest as is the results measured by a suitable flow meter. However, in such feed back arrangement the valve undergoes continuous repositioning, and therefore must have a reliable drive mechanism with little or no backlash. Furthermore, as the fluids may be under pressures up to 100 psi the drive mechanism must operate with a wide range of axial loads. Generally drive mechanisms described in the references were judged as incapable of continuous repositioning, or would exhibit excessive backlash detrimental to smooth fluid control. A second feature found to be overlooked in the current art is the ability to remove the drive mechanism and inspect it without the risk of opening the fluid path.
Reviewing the references cited we find that none of them attempt to solve the full range of the problems posed herein.
SUMMARY OF INVENTION
A free draining fluid path with minimal internal volume and no cracks or crevasses and free of sharp corners is achieved by this invention. Furthermore, the invention provides a smooth throttling path of some length and double containment for the process fluid retained by the thin walled diaphragm. The valve body is machined from a solid block of homogenous material. In this embodiment it is Teflon(PTFE), but could be anything compatible with the anticipated process fluid. An inlet directs the flow stream to an island within the fluid cavity of the valve. A moveable diaphragm and integral throttling surface is a female match to this island. Thus, when the diaphragm is extended and the throttling surface mates with the island the flow stream is shut off from passing through the valve. As the diaphragm is retracted from the closed position the fluid will flow through the gap between the throttling surface mating form and the island into the valve cavity. From the cavity it passes unimpeded to the outlet of the valve body.
The diaphragm is a thin walled flexible membrane sufficiently flexible to be capable of seating down on the island to close off the flow path and progressively retracted from the island to offer decreasing resistance to fluid flow. The diaphragm is designed to be flexible but sufficiently strong enough to with stand fluid pressures up to 60 psi with adequate safety margin. In order to provide safety a secondary diaphragm of similar design is captured immediately above the primary diaphragm. A threaded stem on the upper side of the primary diaphragm provides a means to capture the two diaphragms with a threaded drive shaft. Both diaphragms are machine from Teflon(PTFE) or other suitable material to be compatible with the process fluid. This threaded drive shaft is made from Hastelloy C22. Hastelloy has been chosen for its corrosion resistance. This is an added precaution due to the fact that many corrosives, such as Hydrochloric Acid will produce ions that can leach through Teflon over time. The threaded drive shaft has internal threads for locking the diaphragms and external threads for interfacing with the rotor.
Both diaphragms have squared off shoulders at their periphery. These squared off sections are sized such that when the drive housing is tightened onto the valve body the fluid is sealed within the fluid cavity. A weep hole is provided from the out side of the valve body to the space between the two diaphragms. This, along with a radial canal just outside the diaphragm seals, provide a means of detecting a leak in the primary diaphragm.
The rotor is fixed in position by thrust bearings captured between the rotor and the drive housing. The rotor is free to turn under all vertical loads, and will position the drive shaft, and diaphragms down onto the flow island to close the flow path, or re positioning the diaphragms in the upward direction, to progressively open the path to fluid flow. The lower bearing assemb
Kolarik William Michael
Pratt Wayne L.
Lee Kevin
Nelson Gregory J.
LandOfFree
Double diaphragm precision throttling valve does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Double diaphragm precision throttling valve, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double diaphragm precision throttling valve will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2587384