Patent Application
20090314369
1. Field of the Invention
The present invention relates generally to flow control. In particular, the present invention is directed towards leak detection and backflow prevention (i.e., backflow reduction).
2. Description of Background Art
In many industries it is common practice to interconnect pressurized bulk liquid delivery systems for serving various processes. For example, in the semiconductor industry, most liquid chemistries are delivered under pressure to the wafer fabricating tools. Some of these chemistries are volatile, hazardous, toxic or otherwise chemically aggressive. It is often desirable to provide for the connection of facilities like deionized (DI) water to these bulk distribution systems providing a convenient method to flush-out and neutralize these chemical hazards for process reasons, including for example maintenance.
When two or more liquid delivery systems are interconnected (e.g., for process reasons) there is the potential for cross contamination. These intentional cross connections are often accomplished using valves such as check valves and three-way (or three-port) selector valves. If a small, internal leak (sometimes called a by-pass leak) occurs, the two or more liquids can migrate back and forth across the leaking valve seats contaminating or diluting the process chemistries.
In reality, all valves leak and check valves are particularly bad. Final test criteria for all valve manufacturers is essentially an acceptable leak rate. As valves age and normal wear takes place, leak rates increase. The problem leakage is reverse flow (or backflow). Often these reverse flows occur at very low flow rates [<5 ml/min] and are very difficult to detect. Yet these small leaks allow contamination or dilution of the cross connected liquids.
Backflow can cause expensive damage. High tech processes utilize high purity chemistries to ensure maximum yields and predictable performance. High purity chemistries are expensive. High tech manufacturing tools and fabrication facilities are also expensive. Cross contamination caused by backflow may lead to loss of productivity, reduced yields and semiconductor fabrication plant (FAB) shut downs. Unplanned shut downs to repair/replace leaking components and cleanup contaminated plumbing systems reduce financial performance and introduce unexpected delays into tight delivery schedules. It may take a long time before a small leak is discovered, resulting in the loss of much product and productivity. In bioprocesses, a single malevolent bacteria can ruin a whole batch, perhaps thousands of liters. In medical applications, contaminations can lead to illness, injury or worse.
In addition to contributing to backflow, by-pass leakages also waste valuable chemistries, damage expensive equipment, thereby causing excessive waste. Traditionally, by-pass leakages are detected through visual inspection, which is very insufficient because it is often difficult and time consuming. In addition, there are portions of systems that are difficult or impossible to view, and very small or intermittent leaks are easily overlooked.
Thus, there is a need for an ultra-sensitive leak detection device and a backflow prevention device for critical (or ultra high purity) materials applications.
The present invention overcomes limitations of the prior art by providing a backflow prevention device that sweeps away any liquid leakage using a continuous flow of sweep gas, and a leak detection device that can detect liquid leakage at very low flow rate. This prevents expensive damage that may be caused by backflow and/or leakage and saves chemistries that may be leaked away.
According to one aspect of the present invention, an apparatus for reducing backflow comprises a supply inlet adapted to be connected to a supply source for a liquid; a supply line connecting the supply inlet to a point of use outlet, the supply line comprising a first valve, a first vessel, and a second valve in that order; a sweep gas inlet adapted to be connected to a sweep gas source for a continuous flow of sweep gas, the sweep gas being inert relative to the liquid (and/or relative to the process served); a vent line connecting the sweep gas inlet to a vent outlet; a branch line connecting the first vessel to the vent line, the branch line comprising a vent valve; and a control system that (1) in a liquid supply state, opens the first valve and the second valve and closes the vent valve, and (2) in a stop state, closes the first valve and the second valve and opens the vent valve. When changing from one state to another state, the various valves involved preferably are simultaneously opened and closed, or are opened and closed in a timing that preferably reduces backflow during the transition.
According to another aspect, an apparatus for reducing backflow comprises a supply inlet adapted to be connected to a supply source for a liquid; a first valve, a first vessel and a second valve connecting the supply inlet to a point of use outlet; a sweep gas inlet adapted to be connected to a sweep gas source, the sweep gas being inert relative to the liquid (and/or to the process served); a vent line connecting the sweep gas inlet to a vent outlet; a vent valve connecting the first vessel to the vent line; and a control system that (1) in a liquid supply state, opens the first valve and the second valve and closes the vent valve, and (2) in a stop state, closes the first valve and the second valve and opens the vent valve.
According to another aspect, an apparatus for reducing backflow in a flow control arrangement comprises a sweep gas inlet adapted to be connected to a sweep gas source, the sweep gas being inert relative to a pressurized liquid being distributed in the flow control arrangement; a vent line connecting the sweep gas inlet to a vent outlet; means connecting the vent line to the flow control arrangement; and a control system that (1) in a liquid supply state, prohibits the sweep gas from entering the flow control arrangement and prohibits the pressurized liquid from entering the vent line, and (2) in a stop state, permits the sweep gas to enter the flow control arrangement and permits the pressurized liquid to enter the vent line.
According to another aspect, an apparatus for reducing backflow in a flow control arrangement comprises a sweep gas inlet adapted to be connected to a sweep gas source, the sweep gas being inert relative to a pressurized liquid being distributed in the flow control arrangement; a vent line connecting the sweep gas inlet to a vent outlet; and a one-way valve connecting the flow control arrangement to the vent line, the one-way valve closes when the pressurized liquid is distributed in the flow control arrangement.
According to another aspect, an apparatus for detecting leaks in a flow control arrangement comprises a sweep gas inlet adapted to be connected to a sweep gas source for a continuous flow of sweep gas at a constant flow rate, the sweep gas being inert relative to a liquid being distributed in the flow control arrangement; a vent line connecting the sweep gas inlet to a vent outlet; a branch line connecting the vent line to the flow control arrangement; and a flow switch disposed on the vent line between the branch line and the vent outlet for sensing fluid flowing through the vent line into the vent outlet, the flow switch configured to actuate in response to fluid passing through the vent line into the vent outlet exceeding the constant flow rate, wherein the fluid comprises the sweep gas and any leaked liquid.
According to another aspect, an apparatus for detecting leaks in a flow control arrangement comprises a sweep gas inlet adapted to be connected to a sweep gas source for a continuous flow of sweep gas at a constant flow rate, the sweep gas being non-reactive relative to a liquid being distributed in the flow control arrangement (and/or to a process served); a vent line connecting the sweep gas inlet to a vent outlet; a branch line connecting the vent line to the flow control arrangement; and means for sensing fluid flowing through the vent line into the vent outlet, the means configured to activate in response to fluid passing through the vent line into the vent outlet exceeding the constant flow rate, wherein the fluid comprises the sweep gas and any leaked liquid.
According to another aspect, a method for detecting leaks in a flow control arrangement comprises providing a continuous flow of sweep gas at a constant flow rate through a vent line to a vent outlet; adjusting a flow switch disposed on the vent line to actuate in response to fluid passing through the vent line into the vent outlet exceeding the constant flow rate; receiving a signal indicating that no flow should enter the vent line from the flow control arrangement; opening a vent valve disposed on a branch line connecting the vent line to the flow control arrangement, the flow switch located between the branch line and the vent outlet; detecting that the flow switch actuates; and generating a signal indicating that a leak occurring in the flow control arrangement has been detected.
According to another aspect, an apparatus for reducing backflow and detecting leaks in an interconnected pressurized liquid delivery system comprises a first supply inlet adapted to be connected to a first supply source for a first liquid; a first supply line connecting the first supply inlet to a point of use outlet, the first supply line comprising a first valve, a first vessel, and a second valve in that order; a second supply inlet adapted to be connected to a second supply source for a second liquid; a second supply line connecting the second supply inlet to the point of use outlet, the second supply line comprising a third valve, a second vessel, and a fourth valve in that order; a sweep gas inlet adapted to be connected to a sweep gas source for a continuous flow of sweep gas at a constant flow rate, the sweep gas being inert relative to the first liquid and the second liquid; a vent line connecting the sweep gas inlet to a vent outlet; a first vent valve connecting the vent line with the first vessel; a second vent valve connecting the vent line with the second vessel; a flow switch disposed on the vent line between the two vent valves and the vent outlet for sensing fluid that flow through the vent line into the vent outlet, the flow switch configured to actuate responding to fluid passing through the vent line into the vent outlet exceeding the constant flow rate, wherein the fluid comprises the sweep gas and any leaked liquid; and a control system that (1) in a first liquid supply state, opens the first valve, the second valve, and the second vent valve, and closes the third valve, the fourth valve, and the first vent valve, (2) in a second liquid supply state, opens the third valve, the fourth valve, and the first vent valve, and closes the first valve, the second valve, and the second vent valve, and (3) in a stop state, closes the first valve, the second valve, the third valve, the fourth valve, and opens the first vent valve and the second vent valve.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the disclosed subject matter.
FIGS. (FIGS.) 1A-B are diagrams of an apparatus for preventing backflow in a flow control arrangement according to one embodiment.
The following disclosure and accompanying drawings describe various embodiments that prevent backflow and resulting contamination, and/or detect by-pass leaks in flow control arrangements that dispense liquids (e.g., water, watery mixture such as slurry).
The flow control arrangement shown in
According to one embodiment, the sweep gas is a process-inert gas that does not contaminate the liquid passing through the flow control arrangement for purpose of the underlying process(es) (e.g., subsequent chemical process or bioprocess that the liquid participates). Depending on the liquid and the underlying process(es), the process-inert gas may be non-reactive to the liquid, non-catalytic, and/or non-contaminating. For example, if the liquid being dispensed is deionized water and oxygenated water is deleterious to the underlying process (e.g., because oxygen helps support bacteria), oxygen cannot be used as the sweep gas, even though oxygen does not react with the deionized water. Examples of the process-inert gas include air (e.g., in domestic water systems), purified nitrogen (e.g., in semiconductor fabrication plants), and argon-helium mixture gas, to name a few. As another example, carbon dioxide can be considered process-inert when used to blanket flammable petroleum storage tanks.
Backflows only occur when the supply pressure drops below the dispense pressure of the interconnected supply. For example, a loss of supply pressure in the source 128 may cause vacuum to develop near the source end of the block valve 130. The vacuum may be a result of the siphon effect—when the pressure exerted by the weight of the liquid in the supply line equals or exceeds the diminishing source pressure, the vacuum forms near the source end of the block valve 130. The vacuum may cause backflow by sucking liquid through leaking valves. The backflow prevention device breaks the backflow siphon by channeling leaked liquid to the vent 119 through the vent line 110 and filling the space between the block valves 130, 140 with the process-inert gas. Therefore, if there is any vacuum developed within the flow control arrangement and a block valve leaks, only the process-inert gas is sucked in, and thereby prevents the distributed liquid from being contaminated.
According to one embodiment, the control system (not shown) for the flow control arrangement shown in
One advantage of the implementation illustrated in
The leak detection device shown in
In one embodiment, the flow switch 260 is a standard flow switch or sensor (e.g., magnetic piston and reed switch, Hall effect sensor) operating in a bi-phase flow environment that either actuates (or trips) or not based on the flow rate of mass flowing past it. Examples of the flow switch 260 include Malema™ flow switch models M-60, M-61, and M-62. The flow rate controller 250 controls the flow rate of the sweep gas, and is adjusted to set its flow rate at a constant rate through the vent line 210. The flow rate is set at a level that is inadequate to actuate the flow switch 260, but keeps the flow switch 260 ready to actuate, with any additional mass (e.g., a drop of leaked liquid (approximately 65 microliters)) through the vent line 210 actuating the flow switch 260. The flow rate will vary depending on the situation. In some cases, the flow rate ranges from approximately 5 to 20 SCFH (Standard Cubic Feet per Hour). This flow rate is also called a preload flow rate or a predetermined flow rate. When the flow switch 260 actuates, it generates a pulse signal (i.e., the actuate signal) indicating so. Therefore, each leaking incidence would trigger the flow switch 260 to generate a pulse signal. The flow switch 260 can have an output of its signal to a control system (not shown).
Proper function of the leak detection device can be conveniently and routinely validated. For example, the block valve 230 and the vent valve 220 can be controlled to open, for example, to flush the vent line 210. The flow switch 260 actuates whenever flushes occur. Because the actuation of the flow switch 260 is expected in such a circumstance, the control system can be configured to treat such actuate signals as a validation that confirms the leak detection device functions as expected and safely ignore them. If the actuate signal is not generated when expected, the control system can properly determine that a malfunction has occurred, e.g., either the flow switch 260 malfunctioned, or the valves 220, 230 malfunctioned, or there is no liquid in the source 228. Once the valves 220, 230 are closed, the control system can resume monitoring actuate signals for leak indications.
One of ordinary skill would readily recognize that the leak detection device can be implemented in other variations and incorporated into any flow control arrangement that is susceptible to leaks. For example, the vent valve 220 shown in
As illustrated in
The vent line 310 has a sweep gas inlet connected to a sweep gas source 318 and a vent outlet connected to a vent 319, and is equipped with an orifice (or a flow rate controller) 302 and the check valve 304 near the sweep gas inlet, and a flow switch 340 near the vent outlet. Similar to the leak detection device described above with respect to
According to one embodiment, the device is used in a semiconductor fabrication plant and dispenses chemical mechanical polishing (CMP) slurry and ultra high purity (UHP) deionized water. One skilled in the art would understand that the device can be used in other industries and dispense other types of liquid. In this particular embodiment, the slurry is supplied from a source 338 through the supply line 330 and a dispense line 350 to a point of use (POU) 359. The water is supplied from a source 328 through the supply line 320 and the dispense line 350 to the POU 359.
Based on the control signals received from the control system, the device can selectively dispense slurry or water through the dispense line 350, or not dispense at all. Escaped slurry or water caused by internal leakage is dispensed with the process-inert sweep gas through the vent line 310. In addition, the process-inert sweep gas also fills any vacuum developed within the device (e.g., due to loss of supply pressure in the source). Because the backfill material is a process-inert gas, it will not contaminate or dilute the dispensed liquid (e.g., UHP DI water, CMP slurry).
The control system periodically opens the restricted flow valve 316 to sweep the vent line 310 with deionized water to flush any slurry that may have been deposited in the vent line 310. Because the flush triggers the flow switch 340 to actuate, the control system uses the actuate signal to verify that the device functions normally. After the flush finishes (e.g., seconds or minutes after the restricted flow valve 316 is closed), the control system can resume monitoring the actuate signal from the flow switch 340 for leak detection.
The control system includes logic that generates the control signals for valves and monitors the actuate signals received from the flow switch 340. In one implementation, the control system uses pneumatic logic, which uses compressed gases (usually air or nitrogen) and pneumatic circuits to generate control signals that can be used to operate valves and other control systems. In another implementation, the control system uses electronics and software to implement the logic.
One of ordinary skill can readily recognize that the described invention can be implemented in other variations and not limited to the illustrated examples. For example, the drain flush valve 316 shown in
Unless otherwise indicated, the valves in the described invention can be any kind of valves, such as check valves, wier valves, ball valves, pinch valves, poppet valves, cylinder valves, gate valves, cone valves, triaxial cone valves, plug valves, wafer valves, butterfly valves, and stop valves, to name a few. The control systems include a logic component for generating signals (e.g., control signal for opening/closing a valve, leak detection signal) and receiving signals (e.g., flow switch actuate signal). The logic component can include mechanical, pneumatic, hydraulic, or electronic circuits, for example.
This application claims the benefit of U.S. Provisional Application No. 61/118,765, filed Dec. 1, 2008, and U.S. Provisional Application No. 61/074,663, filed Jun. 22, 2008, both of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61118765 | Dec 2008 | US | |
| 61074663 | Jun 2008 | US |
