Variable orifice valve

Details Variable orifice valve Variable orifice valve

1999-10-25

2001-12-04

Michalsky, Gerald A. (Department: 3753)

Fluid handling

Removable valve head and seat unit

C137S487500, C251S129110, C251S212000, C251S901000

Reexamination Certificate

active

06325096

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a variable orifice valve which is most useful for gas handling systems that require a low pressure drop on the order of up to 5 inches of water, and is particularly useful for vacuum systems that require an extremely low pressure drop across the vacuum control valve.
BACKGROUND OF THE INVENTION
There are innumerable industrial processes that require control of air flow in a duct. Such control is provided in part by valves. For low pressure vacuum systems, fine control is needed. Currently available valves, and valve systems including valve controllers, are inadequate in many respects.
Ideally, such valves create when open little or no restriction in the duct. However, rotatable vane-type valves, and piston-type valves each create very substantial restrictions (and thus pressure drop across the valve) even when fully open. Such is unacceptable for many applications.
In addition, such valves should operate as quickly as possible in order to prevent pressure fluctuations that can affect air flow upstream of the valve, and their operation should preferably be linear, which simplifies and speeds their control. Butterfly valves have a very non-linear relationship between position and open area, and are relatively slow to operate. These issues are particularly critical in applications that require constant, controlled air flow in an industrial process. One example of such is the fine control of air flow required in a semiconductor wafer resist coating operation; the air flow in part defines the quality of the resist coat, so the aim is to keep the air flow constant. However, perturbations in the vacuum system downstream of the resist coating chamber cause pressure fluctuations that propagate upstream to the chamber, thus disturbing the air flow. It is thus an aim in such systems to have a valve, and air control system using such valve, that creates essentially zero pressure drop when fully open, and provides for fine and nearly instantaneous control of the valve orifice size, to prevent downstream pressure perturbations from propagating upstream past the valve, and thus affect the flow of air in a resist coating chamber located upstream of the valve.
SUMMARY OF THE INVENTION
It is therefore the primary object of this invention to provide a fluid control valve, and system using such valve, that provides very fast, either essentially linear or tailored response, and is adjustable from a fully open position in which it creates virtually no restriction in the fluid duct, to a fully closed position in which the duct is essentially closed.
The invention features in one embodiment a valve comprising a band with opposed openings. As the band is moved, the overlap of the opposed openings changes to vary the orifice created by such overlap. Alternatively, the band can be replaced by members, each defining an opening, which are movable cooperatively, transversely to the fluid flow, to vary the orifice area created by the overlapping openings. In an alternative embodiment, the valve comprises two or more valve leaves which together defamed the orifice, and are cooperatively pivoted by a single drive system in order to accomplish the variable orifice.
Featured herein is a variable orifice valve for controlling fluid flow in a conduit, comprising: two or more movable members (such as vanes or portions of a band which together define an opening for passing the fluid therethrough; means for mounting the members transverse to the direction of fluid flow in the conduit, so that the opening is at least partially in the conduit; and means for moving the members relative to the conduit, to change the amount of the opening (the orifice size) exposed to fluid flow.
When the members define band portions, the band may have two openings, which may be selectively overlapping. Preferably, one opening is downstream of the other opening. The means for moving may include a first roller outside and on one side of the conduit, and a second roller outside and on the other side of the conduit. The band is preferably wrapped at least partially around each such roller. The means for moving may further include means for rotating the first roller to change the relative positions of the openings. The means for rotating the first roller may include a drive motor which drives the periphery of the first roller. The valve may further include idler rollers proximate each of the first and second rollers, and around which the band is partially wrapped.
The openings define an orifice shape having approximately the same circumferential shape as the duct, so that the valve when fully open presents little or no restriction in the duct. For a circular duct, the orifice is preferably generally circular. Preferably as well, the band has two ends, and both ends are fixed to the first roller. The band may be virtually continuous, and wrapped most of the way around each roller. The means for rotating may rotate the first roller so that any portion of the band which is located within the duct does not touch the first roller.
The band may include a relatively stiff portion located in the conduit, and may further include a relatively flexible portion located outside of the conduit. The valve may further include means for determining the position of the band (and thus the openings) relative to the conduit. The movable members may be housed in a valve cartridge which is removably held in a valve housing. In this arrangement, the means for moving the members may itself be movable relative to the housing, so that it can be disengaged from the cartridge to facilitate cartridge removal.
The valve system may further include means for determining the fluid pressure in the conduit at a first location upstream of the band. The means for moving may be responsive to this means for determining fluid pressure. The valve system may further include means for sensing the fluid pressure at a second location upstream of the first location. The valve system may still further include means for establishing a fluid pressure set point. The means for moving may be further responsive to the means for sensing and the means for establishing a fluid set point.
Featured in another embodiment is a variable orifice low pressure gas flow control valve for controlling fluid flow in a conduit, comprising: a drive roller; a tensioning roller; an at least partially flexible band defining two openings which are aligned within the conduit in a valve fully open position, the band being at least partially wrapped around both the drive and tensioning rollers, the portions of the band proximate the openings lying very close together in the conduit, to minimize fluid leakage past the band that is not through the openings; and means for rotating the drive roller to move the band and thus change the relative overlap of the two to openings, to thereby change the orifice size.
Featured in yet another embodiment is a variable orifice gas flow control system for maintaining a relatively constant gas flow at a control location in a vacuum system, comprising: means for establishing a pressure set point; a variable orifice valve in the vacuum system, the valve having a movable band spanning the vacuum system, and defining an opening with an open area which is variable by movement of the band; means for determining the pressure at two spaced locations of the vacuum system, a first location proximate the control location, and the second location proximate and upstream of the valve; and means, responsive to the pressure set point and the two determined pressures, for moving the band to drive the pressure at the first location toward the pressure set point.
In still another embodiment, this invention features a variable orifice valve for controlling fluid flow in a conduit, comprising: a first member mounted at least partially in the conduit, and defining a first opening; a second member mounted at least partially in the conduit proximate the first member, and defining a second opening; and means for moving the first and second members cooperativel

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