Air flow control device with very tight close off

Abstract

An air flow control device consisting of air foil designed vanes for accurate modulation of the air into and out of a space. This damper includes end seals in which the ends of the air foil control vanes are located. Upon closure of the vanes the end seals prevent the air from bypassing the vanes and a very tight close off is realized.

Description

FIELD OF INVENTION

This invention relates to air flow devices which are capable of very accurate control of air flow or pressure and are additionally capable of very tight close off.

BACKGROUND OF THE INVENTION

Many processes require very accurate control of air flow and/or pressure. Typical processes include clean spaces pharmaceutical manufacturing, electronic manufacturing and very specialized laboratories. Accurate and repeatable control over air flow and/or pressure is critical for the success of these processes and is particularly difficult where the upstream pressures vary due to changing fan speeds. The industry uses a phrase “pressure independent” which means that the control of the air flow must be repeatable and independent of the up stream pressure. For these critical spaces good practice suggests that the pressure or volume control must be within 0.5% of the design criteria when the pressure varies from say 1″ (250 Pa) to say 4 in (1000 Pa). The preferred embodiment disclosed here-in utilizes an air foil shaped profile which is expandable during modulation presenting an air foil shape to the air stream at modulation points. This air flow control device is ideally suited for accurate air flow control and exhibits the required 0.5% maximum variation by independent test. This accuracy was taught in an earlier Pat. No. 3,010,518 (Day) wherein the performance of a similar design was described as being without hystersis. However Day does not teach the need to combine accurate air flow modulation with the ability to tightly close off the airflow.

Many special processes require not only accurate control over space pressures but also decontamination of these spaces on a periodic basis. Decontamination procedures require that the supply and extract systems close tightly to prevent the decontamination gasses from being distributed throughout the building In the past good decontamination procedures have included two specific devices—an accurate air flow control valve to maintain space pressures during normal operation and a separate valve to close-off the space during contamination. A popular close off valve design uses a flat or slightly curved disk with a raised edge. When rotated to a closed position the edge of this disk presses into a rubber seal closing off the flow of air. A common name for this item is a “Bubble Tight” damper. This valve design was developed many years ago for the nuclear industry. Another valve design for tight close off applications is described in Pat. No. 4,457,336 (Allen et al.) Both of these solutions are expensive, occupy a relatively large amount of space and require a separate high pressure actuator. These devices do not accurately modulate the air flow but are used only as a very tight close-off valve.

During the last phase of the decontamination cycle some procedures utilize a “scavenge” mode where a small amount of supply and extract air is used to scavenge any residual decontamination gases from the space prior to human occupancy. This flow rate is often in the range of 5% to !0% of the normal flow rate. To accurately control this very small amount of air the valve must modulate these very low air flows without hystersis while operating in a very close to closed position.

The instant invention shows an air flow control valve with a rectangular casing. Several other flow control methods use rectangular shapes. An example is Pat. No. 3,768,512 (Lahaye) which focuses on high temperature applications and teaches the use of the flexibility of the material at high temperatures. It does not teach the need for hystersis free modulation of air flow or the need for very tight close off.

Other air control methods can also be designed with rectangular casings. A common design is based on a series of rectangular blades mounted in parallel within a casing. Pat. No. 4,766,807 (Davis) is an example. Air flow modulation results from the rotation of the blades from an open to closed position. The performance of a series of rotating flat plate rectangular blades is not accurate or repeatable due to the inherent hystersis of this design. The hystersis is due to the formation of unstable vortices in the negative pressure area behind the blades. This design is not suitable for very accurate pressure or flow control. This damper design is often used for non critical applications such as office buildings and commercial stores and outside air inlets where low cost is important. If minimal leakage is desired rubber seals are fixed to the edge of the rotating blades as well as on the sides of the blades. During rotation the sides seals rub against the inner surfaces of the casing and as rotation continues the rubber seals wear with increasing leakage rates.

Some air flow control valves are based on a tubular shape. One tubular design includes a cone which moves laterally within a venturi shaped throat. Pat. No. 3,204,664 (Gorchev) is an example. This cone design sometimes uses a rubber ring fixed to the moving cone to help reduce the leakage. The rubber ring wears as it rubs against the inner surface of the throat permitting a sizeable increase in the leakage during the life of the damper. Another tubular design includes a rotatable disk to control the flow of air through the tubular casing. For low leakage a circular strip of rubber is fixed to the circumference of the disk. As with any device with frictional contact this rubber disk wears during normal modulation significantly increasing the leakage past the damper blade during the life of the product.

OBJECTIVES OF THIS INVENTION

An air flow control valve which includes a series of expandable air foil shaped vanes which permits modulation of the air with excellent accuracy and repeatability and without hystersis. This valve also includes an integral sealing system which prevents by-passing of the air for very tight shut-off.

An air flow control valve which will modulate not only normal flow rates but also very low flow rates permitting many possible air flow strategies with excellent accuracy and no air bypassing the modulating vanes.

An air flow control valve which includes a sealing system which prevents the flow of air upon valve closure. The sealing system includes two elastomeric side seals which are fixed to the side walls of the valve. Each side seal includes a series of cavities which duplicates the profile of a fully expanded air foil vane. When the air foil shapes expand into the cavities the side seals prevent the flow of air from by-passing either end of vane profile. This tight close off is by compression which will not wear the side seals during the normal life of the valve. The original very low leakage rate is maintained for the life of the device. Also included are a series of vane mid span seals which upon vane expansion compress and prevents the flow of air between the vanes.

An air flow valve which provides accurate modulation and very tight close-off in a compact, self contained assembly with a single source of activation.

An air flow control valve with an air sealing means which is inflatable by pneumatic actuation. Where pneumatic actuation is not available an alternate means of actuation may be utilized achieving the same objectives

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a series of fully open (deflated) air foil shaped vanes (1) which are able to be expanded in parallel by a pneumatic signal through a tube (4). These vanes are positioned in a fixed relationship with each other by a set of vane holders (6) and the assembly is mounted in a casing. The casing has two side pieces (7) and two top pieces (8). Maximum air flow through the damper is with fully open vanes. Two side seals (2) are shown fixed to each of the two side pieces (7).

FIG. 2 shows a partially open (partially inflated) series of air foil shaped vanes (1) and their relationship with the side seals (2). Normal modulating air flow is with the vanes partially open.

FIG. 3 shows a fully closed (inflated) series of air foil shaped vanes (1) and the very close fit of the vanes within the cavities (18) in the side seals (2). With the vanes (1) fully closed compressing the mid span vane seals (17) and the ends of the vanes bearing on the cavities in the side seals (2) any possible passage of air is very tightly closed off.

FIG. 4 shows an end view and a detail of the relationship between the end of each vane (1) and the cavity (18) in the end seals (2). The end of each vane (1) terminates within the width of each side seal (2) and bears on the width of the side seal (2) when fully inflated.

FIG. 5 shows one side seal (2) configuration with cavities (18) accurately duplicating the profile of the expanded air foil vanes (1).

There are alternate means of actuation which are suitable for the enclosed invention. The preferred invention describes an inflatable air foil profile. In certain applications where pneumatic inflation is not practical or not desired mechanical expansion of the airfoil profile is useful. The air foil shaped vane can alternatively be uniformly expanded by a cam shaped device or a similar shape. Additionally the air foil profile can be fabricated in movable and fixed halves resulting is a semi-airfoil vane. By mechanically actuating the moveable half vane performance similar to the air foil shaped vane can be achieved.

FIG. 6 shows a partially open series of air foil vanes (1) actuated by a cam shaped device (18) located within an air foil profile (1). The cam shaped device (18) extends the full length of the air foil vane. Upon rotation of the cam shaped device (18) the air foil vane profile (1) will expand uniformly. A series of cam actuated vanes (1) are installed in parallel within a casing forming an accurate air flow control damper. The relationship between the vanes (1), the end seal (2) and the mid-span vane seals (17) are shown. The rotation of the cams are accomplished through a series of eccentric arms attached to a common rod and then to an actuator.

FIG. 7 shows a fully closed series of air foil vanes (1) actuated by a cam shaped device (18) located within an air foil profile (1). The cam shaped device extends the full length of the air foil vane. Upon a 90 degree rotation of the cam shaped device (18) the air foil vane profile (1) will expand uniformly and tightly close. With the vanes (1) fully closed compressing the mid span vane seals (17) and the ends of the vanes bearing on cavities in the side seals (2) the damper is tightly closed.

FIG. 8. shows a mechanically actuated damper with fully open semi air-foil vanes. The fully open half vane permits the maximum amount of air to pass through the damper. This damper includes an actuator (12) which extends and retracts a rod (16) within the casing. The rod is connected to a moveable half vane (14) which opens and closes upon the extension and retraction of the actuator rod (16). The movable half vane is hinged (15) to the forward edge of the fixed half vane (13). This fixed half vane (13) is fastened to a set of vane supports (6). By rotating the movable half vane (14) the free area through the damper can be changed modulating the air flowing through the damper. The side seals (2) are applied to the two inner side (7) surfaces of the casing reducing the air bypassing the ends of the vanes to a very small amount. A mid span vane seal (17) is attached to the center of the fixed vane.

FIG. 9 Shows a mechanically actuated damper with fully closed semi air foil vanes. The fully closed half vanes (14) permits the damper to effectively prevent any air from passing through the damper. The side seals (2) are applied to each inner side (7) surfaces of the casing preventing the air from bypassing the ends of the vanes. The mid span vane seals (17) will compress as the movable half vanes close on the fixed half vanes preventing any air from passing through the closed vanes.

FIG. 10 shows a detail of a the mid span vane seal (17) used on a semi airfoil vane. Also shown are the moveable half (13) the hinge (15) and the fixed half (14). While this semi airfoil design develops a small amount of aerodynamic hystersis the design is suitable for mechanical actuation.

This damper design is also well suited for side and blade seals and will close with very low leakage in the same manner as the inflatable air foil vane design described previously. The side seals and mid span vane seals being under compression (not friction) will also maintain the very low leakage performance for the life of the system.

Claims

1. In an air flow control valve comprising of a series of expandable air foil profiles, a means of supporting the air flow profiles, a casing enclosing the air foil profiles and a set of side seals located at each end of the expanded air foil profiles each side seal being permanently fixed to the interior surface of the casing and each side seal containing an accurate profile of each expanded blade profile

2. In claim 1 the side seals being a thick enough to provide a support of the expandable air foil profiles said support preventing any bypass of the air when the air foil profiles are fully closed against the side seals.

3. In claim 2 said side seal being composed of a compressible material and upon full expansion of the profiles the amount of compression of the side seals being sufficient to prevent the bypassing of air.

4. In claim 3 a vane seal consisting of a strip of thin compressible material affixed to the center of each of the air foil vanes and extending the length of each vane profile and pressing on an adjacent profile preventing passing of air between the profiles when the profiles are fully closed.

5. In an air flow control valve comprising of a series of air foil profiles expandable by means of a pneumatic signal, means of supporting the air flow profiles a casing enclosing the air blade foil profiles and a set of side seals located at each end of the expanded air foil profiles each side seal being permanently fixed to the interior surface of the casing the side seals containing an accurate profile of each expanded blade profile

6. In claim 5 the side seals being a thick enough to provide a support of the expandable air foil profiles said the support preventing any bypass of the air when the air foil profiles are fully expanded.

7. In claim 6 said side seal being composed of a compressible material and upon full expansion of the profiles the amount of compression of the side seals being sufficient to prevent the bypassing of air.

8. In claim 7 a vane seal consisting of a strip of compressible material affixed to the center of each of the air foil vanes and extending the length of each profile and pressing on an adjacent profile preventing passing of air between the profiles when the profiles are fully closed.

9. In an air flow control valve comprising of a series of air foil profiles expandable by means of mechanical actuation, means of supporting the air flow profiles a casing enclosing the air blade foil profiles and a set of side seals located at each end of the expanded air foil profiles each side seal being permanently fixed to the interior surface of the casing and each side seal contains an accurate profile of each expanded blade profile

10. In claim 9 the side seals being a thick enough to provide a support of the expandable air foil profiles said the support preventing any bypass of the air when the air foil profiles are fully expanded.

11. In claim 10 said side seal being composed of a compressible material and upon full expansion of the profiles the amount of compression of the side seals being sufficient to prevent the bypassing of air.

12. In claim 11 a vane seal consisting of a strip of thin compressible material affixed to the center of each of the air foil vanes and extending the length of each vane profile and pressing on an adjacent profile preventing passing of air between the profiles when the profiles are fully closed.

13. In an air flow control valve comprising of a series of semi air foil profiles expandable by means of mechanical expansion, means of supporting the air flow profiles a casing enclosing the air blade foil profiles and a set of side seals located at each end of the expanded air foil profiles each side seal being permanently fixed to the interior surface of the casing and the side seals containing an accurate profile of each expanded blade profile

14. In claim 13 the side seals being a thick enough to provide a support of the expandable air foil profiles said the support preventing any bypass of the air when the air foil profiles are fully expanded.

15. In claim 14 said side seal being composed of a compressible material and upon full expansion of the profiles the amount of compression of the side seals being sufficient to prevent the bypassing of air.

16. In claim 15 a vane seal consisting of a strip of thin compressible material affixed to the center of each of the air foil vanes and extending the length of each vane profile and pressing on an adjacent profile preventing passing of air between the profiles when the profiles are fully expanded.