GB1603072A

GB1603072A - Valve for air flow control

Info

Publication number: GB1603072A
Application number: GB24178/78A
Authority: GB
Original assignee: Spiro Investment AG
Current assignee: Spiro Investment AG
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-11-18

Description

(54) VALVE FOR AIR FLOW CONTROL (71) We, SPIRO INVESTMENT, S.A., a Joint Stock Company organised under the laws of Switzerland, of Industriestrasse, CH-3178 Bösingen, Switzerland, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to fluid-flow control valves. More particularly, the invention relates to damper valves for controlling air flow in ventilating systems.

Numerous kinds of control valves have been used in ventilating and other systems, and these include iris and butterfly valves. Most of these valves lack the advantage of simplicity of operation, and involve disadvantages such as high noise levels during operation in intermediate positions.

It is an object of the present invention to provide a fluid-flow control valve which has simple operating characteristics and in which the disadvantage of exhibiting high noise levels in intermediate positions is at least reduced.

According to the present invention there is provided a valve for controlling air flow through ducting, comprising an axially extending valve casing having an axial air inlet and an axial air outlet for connection respectively to ducting through which the air flow is to be controlled, and a flared inner face which widens outwardly in a direction away from said air inlet towards said air outlet; and a discshaped valve member mounted coaxially within said valve casing for axial movement relatively to said valve casing between said air inlet and said air outlet of said valve casing to vary the area of a valve opening defined between the outer periphery of said valve member and said inner face; said valve casing providing a substantially unobstructed axial air flow passage from the inlet end of said inner face to said valve opening and from said valve opening to said axial air outlet; the axial length of said valve member being small in relation to the axial length of said inner face; said valve member comprising a generally flat front face directed towards said air inlet, a more sharply curved peripheral shoulder extending outwardly and rearwardly from said front face to define a radiused entry to said valve opening, and a rear edge terminating at the periphery of the valve member to define a stepped exit from said valve opening; and the shape of said inner face of the valve casing being such that the variation in the area of said valve opening with axial movement of said valve member compensates for the corresponding variation in the drag coefficients due to said more sharply curved shoulder, said rear edge of the valve member and the portion of the inner face of the valve casing forming the valve opening, whereby for any given pressure drop across a combination of duct and valve, the variation in the volume of air flow in relation to the position of said valve member is linear.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a sectional elevation showing a damper valve according to the invention; Figure 2 is a view of the inflow end of the valve; and Figure 3 is a diagram illustrating the shaping of the valve casing and valve member.

Referring to the drawings, the damper valve comprises a casing 10 in an air duct indicated at 11. The casing extends from its inflow end 12 where a valve seating 13 is provided, to a spider 14 at its outflow end 15. A valve member 16 formed from sheet metal to have a convex front face 17 and a concave rear face, is movable along a tubular spindle 18 which extends axially along the casing between the rear spider 14 and another spider 19 at the inflow end 12.

The valve member 16 is movable from a closed position at the valve seating 13, to a fully-open position in engagement with hub 20 of the rear spider 14, by means of, in this embodiment, a hydraulic control system. This system comprises a piston 21 which is carried at the end of an actuating rod 22 for movement within a cylinder 23 which is mounted on the casing 10. Hydraulic fluid from cylinder 23 passes through a bore 24 in the upper limb of the front spider 19, to pass through boss 25 of the spider and enter the tubular spindle 18 which provides a cylinder 26.

Piston 27 is movable within the cylinder 26 on one end of a rod 28 which is secured, at its other end, through a tapped disc 29 backed by a lock nut 30, to a tubular sleeve 31. The sleeve is telescopically mounted on the spindle 18 and carries the valve member 16 which is urged towards the closed position by compression spring 32.

Thus, when the rod 22 is displaced to the right, from the position shown in Figure 1, the valve member 16 is displaced to the left from the solid-line to the .broken-line positions shown. If the cylinders 23 and 26 are of the same bore, the two displacements will be the same.

Modifications may be made. For example, the piston rod may be threaded for manual or electric rotation to produce displacement, or may be pneumatically actuated.

The valve casing 10 has an inner face 33 which is so shaped in relation to the drag characteristics of the valve member that the degree of linear movement of the valve member is directly proportional to the effective degree of valve opening.

That is to say that for any given supply pressure of air supplied via the air duct 11 to the valve, the relationship between the axial movement of the valve member and the volume of air flow through the duct and valve will be linear. Thus, for example, if the distance travelled by the valve member 16 in moving from the closed position to the fully-open position is 12 cm., and the air flow through the fully-open valve is 60 m3 per minute, the air flow through the annular gap between the periphery of the valve member and the casing 33 will be 20 m3 per minute when the valve has moved 4 cm. from the closed position.

Referring to the section at the inflow end of the valve casing, it is desirable to have the seating 13 curved to approximately the same radius as the peripheral part of the valve member 17.

To reduce operational noise levels even further, particularly at higher air speeds, a sleeve of sound deadening material may be provided to surround both ends of the duct 11 for a length equal to three or four times the diameter of the duct.

It is also to be noted that the curvature of the major central part of the front face of the valve member 17 is slight, and this almost-flat formation is highly effective in deadening noise, such as fan noise, which travels axially along the duct.

Furthermore, an annular spoiler indicated at 35 may be carried by the valve member 17, spaced from its rear face, to reduce turbulence and thus also reduce noise.

The form of the face 33 could be determined experimentally, starting with a malleable casing of frusto-conical form as indicated by broken lines 36, and removing or adding material as required at each one of a substantial number of positions of the valve member 16. Alternatively, in accordance with a further feature of the invention, the form can be determined at least partly by calculations described below.

The method of calculating mathematically the desired correction of the valve surface 33 will now be described in more detail, referring to Figure 3 in which the relevant dimensions of a valve of the general construction described above are shown.

In a valve of the construction described above the total drag over the valve is made up of the following components.

1. Entrance to the Valve The reduction in cross-sectional area in relation to the duct at the entrance to the valve casing produces a drag coefficient which is constant, and which may be reduced by a minimum by the provision of well rounded corners to the entry to the valve casing and of streamlined spiders for support of the spindle of the valve member.

The drag coefficient appropriate to this part of the valve will hereinafter be designated Pis 2. Entrance to the Valve Member Here, a further area reduction involves a contraction loss, which is dependent of the formation of the valve member 17 and in particular the outer radiused skirt thereof. The drag coefficient of the entrance to the valve member is a variable function of the position of the valve member, and will hereinafter be designated pj.

3. Exit of the Valve Member At the exit of the valve member a sudden area increase involves vortex and friction losses. The drag coefficient is also a variable function of the position of the valve member and will hereinafter be designated Pu 4. Shaped Section of the Valve Casing Where the overall length L of the part of movement of the valve member 17 is substantial, and the casing converges rapidly, the diverging area containing the valve member and the spindle, hereinafter referred to as the diffuser section, produces a drag coefficient which varies slightly according to the position of the valve member. This drag coefficient is hereinafter referred to as Pd 5. Exit of the Valve The drag coefficient at this point may be reduced by streamlining of the spider and support for the spindle of the valve member.The drag coefficient is constant and will be designated Pus From the above it will be seen that of the five major drag coefficients p" Pu and Pd are variable. The most significant variation in the total drag is due to Pu followed by p and Pd.

Assuming that the form of the valve throat is required to give a linear relationship between the axial control movement of the valve member and the volume of air flow through the valve at any given constant pressure drop across the valve, the calculation of the correction required to compensate for the variable drag coefficient of the valve can be calculated in terms of the pressure drop required across the valve for a constant volume of air flow through the valve at each control position of the valve member. By considering the pressure drop in relation to constant volume of flow through the valve, the drag coefficients of the inlet and outlet of the valve remain constant and can be disregarded for initial calculations.

In order two derive a table of desired pressure drops for the respective positions of the valve member, firstly the pressure drop across the valve in the fully open position is calculated in relation to an air flow of unit volume through the entry duct to the valve. Since the most significant drag coefficient is Pu, this pressure drop may be expressed as V Pu=pu.vu2.- (I) 2 where Pu=pressure drop y=density of air vu=velocity of air flow through the exit from the valve member.

Since the density of air represents a constant, for the purpose of the calculation of relative values of the valve, let Pu (11) V 2 so that Pu'=Pu vu2 (III) According to the known "Carnot" equation, the drag coefficient at the outlet from the valve member may be expressed as

where Au=the area of the annular exit opening from the valve member, and Athe total area of the exit from the valve casing.

Assuming unit volume of flow v, through the entry duct to the valve, v,xA, vu= (V) Au Thus, the pressure drop P:,,=,, at the fully open position of the valve can be expressed as follows:-

2. From the initially determined pressure drop of the fully open valve, the desired pressure drops for each position of the valve member can be calculated from the following formula: 1 L2 wherein Lithe fraction of movement of the valve member from its closed position.

3. Having determined a table of wanted pressure drops, the corresponding area of the exit from the valve member and thus radial dimension ru of the valve casing at the exit from the valve member in corresponding positions of the latter can be calculated in relation to the desired pressure drop from the above formula (VI), using a successive approximation method.

4. Having derived a first correction for the contour of the valve casing, a calculation is now made of the pressure drop due to the drag coefficient for the entrance part of the valve member, in the respective positions of the valve member.

The formula for pressure drop at the entrance to the valve member can be derived in a similar manner to that for the exit valve member and is as follows:- Pj=pixvu2. (VIII) From the form of valve member illustrated in Figure 3, the following formula can be established for drag coefficient:

wherein A,' is the cross-sectional area of the valve casing at the position of the front face of the valve member. This holds true for Au > 0.2 A,' Below this value instability occurs.

5. From the previously established values of Pú and Pj, the calculation of the actually required pressure drop for the exit part of the valve member in its respective positions can be calculated from the following formula:

6. The radial dimension ru of the valve casing at the respective axial positions can now be recorrected using P!WL in place of Pú in formula (VI).

7. Further corrections of Au (ru) are now made in the unstable distance Au < 0,2 A, or in this case for the positions 1/16, 1/32, 1/64, 1/128 these corrections are determined experimentally.

8. Further corrections are made after calculation for pressure drop along the diffuser part of the valve casing; derived from Carnot's equation:-

where A0=the cross-sectional area of the valve member.

8. Finally, the contributions to the drag which derive from the inlet and outlet parts of the valve are added to calculate the total drag over the valve.

EXAMPLE In a specific Example of valve as shown in Figure 3 and corrected by the above methods, the valve casing had a circular cross-section with maximum internal diameter 156 mm, a valve member had an external diameter of 108 mm and a regulating distance of movement of 90 mm with an axial dimension of 22.5 mm and an outer skirt of radius 22.5 mm, and the radial dimension ru of the valve casing at each axial position L of the exit part of the valve casing was as follows::- L Ru(mm) 1/1 78 3/4 74.31 1/2 69.81 1/4 63.85 1/8 59.82 1/16 57.33 1/32 55.88 1/64 55.03 1/128 54.56 The valves according to the invention have the obvious advantage of simplicity in operation and control, and this is particularly attractive to conditions of remote control and to the operation of valves in balance, for example, in ventilating systems where inlet and exhaust valves are coupled to operate in unison, or where hot and cold air flows are mixed in inverse proportions.

Another application of the valve is in controlling air flow pressures and maintaining such pressures at constant values.

A further attraction of the valve described above is that the flow is always around the periphery of the valve member 16 and thus remote from the centre of the air duct where the flow speed tends to be greatest. As a result, the noise level in operation is minimised, as opposed to, for example, iris valves where high-speed central gas flow may produce high noise levels, particularly in the lower range of valve openings.

WHAT WE CLAIM IS: 1. A valve for controlling air flow through ducting, comprising an axially extending valve casing having an axial air inlet and an axial air outlet for connection respectively to ducting through which the air flow is to be controlled,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

6. The radial dimension ru of the valve casing at the respective axial positions can now be recorrected using P!WL in place of Pú in formula (VI).

7. Further corrections of Au (ru) are now made in the unstable distance Au < 0,2 A, or in this case for the positions 1/16, 1/32, 1/64, 1/128 these corrections are determined experimentally.

8. Further corrections are made after calculation for pressure drop along the diffuser part of the valve casing; derived from Carnot's equation:-

where A0=the cross-sectional area of the valve member.

8. Finally, the contributions to the drag which derive from the inlet and outlet parts of the valve are added to calculate the total drag over the valve.

EXAMPLE In a specific Example of valve as shown in Figure 3 and corrected by the above methods, the valve casing had a circular cross-section with maximum internal diameter 156 mm, a valve member had an external diameter of 108 mm and a regulating distance of movement of 90 mm with an axial dimension of 22.5 mm and an outer skirt of radius 22.5 mm, and the radial dimension ru of the valve casing at each axial position L of the exit part of the valve casing was as follows::- L Ru(mm) 1/1 78 3/4 74.31 1/2 69.81 1/4 63.85 1/8 59.82 1/16 57.33 1/32 55.88 1/64 55.03 1/128 54.56 The valves according to the invention have the obvious advantage of simplicity in operation and control, and this is particularly attractive to conditions of remote control and to the operation of valves in balance, for example, in ventilating systems where inlet and exhaust valves are coupled to operate in unison, or where hot and cold air flows are mixed in inverse proportions.

Another application of the valve is in controlling air flow pressures and maintaining such pressures at constant values.

A further attraction of the valve described above is that the flow is always around the periphery of the valve member 16 and thus remote from the centre of the air duct where the flow speed tends to be greatest. As a result, the noise level in operation is minimised, as opposed to, for example, iris valves where high-speed central gas flow may produce high noise levels, particularly in the lower range of valve openings.

WHAT WE CLAIM IS:

1. A valve for controlling air flow through ducting, comprising an axially extending valve casing having an axial air inlet and an axial air outlet for connection respectively to ducting through which the air flow is to be controlled,

and a flared inner face which widens outwardly in a direction away from said air inlet towards said air outlet; and a disc-shaped valve member mounted coaxially within said valve casing for axial movement relatively to said valve casing between said air inlet and said air outlet of said valve casing to vary the area of a valve opening defined between the outer periphery of said valve member and said inner face; said valve casing providing a substantially unobstructed axial air flow passage from the inlet end of said inner face to said valve opening and from said valve opening to said axial air outlet; the axial length of said valve member being small in relation to the axial length of said inner face; said valve member comprising a generally flat front face directed towards said air inlet, a more sharply curved peripheral shoulder extending outwardly and rearwardly from said front face to define a radiused entry to said entry opening, and a rear edge terminating at the periphery of the valve member to define a stepped exit from said valve opening; and the shape of said inner face of the valve casing being such that the variation in the area of said valve opening with axial movement of said valve member compensates for the corresponding variation in the drag coefficients due to said more sharply curved shoulder, said rear edge of the valve member and the portion of the inner face of the valve casing forming the valve opening, whereby for any given pressure drop across a combination of duct and valve, the variation in the volume of air flow in relation to the position of said valve member is linear.

2. A fluid-flow control valve as claimed in Claim 1, in which said valve member is mounted on a central spindle which extends axially between the ends of the valve casing.

3. A fluid-flow control valve as claimed in Claim 2, in which said valve member is movable by means of a hydraulic control system including a piston-and-cylinder device provided in said spindle.

4. A fluid-flow control valve as claimed in any preceding claim, ili which the shape of said inner face of the valve casing is determined by calculations substantially as hereinbefore described.

5. A damper valve for an air-conditioning system, the valve being substantially as hereinbefore described with reference to the accompanying drawings.

6. An air flow control system incorporating at least two interconnected valves as claimed in any preceding claim.

7. A method of producing a fluid-flow control valve including the step of deriving the shape of the valve casing by means of the calculations herein described.