GB2073404A

GB2073404A - Dampers

Info

Publication number: GB2073404A
Application number: GB8106462A
Authority: GB
Original assignee: FAREX AS
Current assignee: FAREX AS
Priority date: 1980-03-05
Filing date: 1981-03-02
Publication date: 1981-10-14
Also published as: NO810670L; DK97681A; FI810596L; SE441547B; DE3106964A1; FR2477665B1; FR2477665A1; NO149560C; FI64995C; NO149560B; SE8001750L; DE3106964C2; GB2073404B; FI64995B; CH654399A5

Abstract

An automatic regulating valve for ventilation systems intended to permit a substantially constant volume of air to pass therethrough per unit of time with a varying difference in pressure between the air- infeed side and the air-outfeed side, includes a valve plate (2%) which is mounted in a valve housing (1), for rotation on a shaft (3) which is arranged to cooperate with means for counteracting movement of the valve plate (2%) towards its valve- closing position. The part of the valve plate (2) located beneath the central plane of the housing covers a smaller part of the cross-sectional area of the valve housing (1) than the part of the valve plate located above said plane. <IMAGE>

Description

SPECIFICATION Automatic regulating valve The present invention relates to an automatic regulating valve for ventilation systems, and in particular to such a valve which is arranged to permit a substantially constant volume of air to pass therethrough (per unit of time) with a varying pressure difference between the air input side and the air output side. Known valves include a valve plate which is pivotally mounted on a horizontal shaft in a valve housing, and means for counteracting movement of the valve plate towards a closing position, the part of the valve plate located above said pivot shaft being arranged to swing towards the direction of air flow and towards a vertical plane as the valve plate pivots towards said closing position.

One problem with regulating valves of this kind is that the closing moment resulting from the generated air flow greatly increases as the valve plate approaches its valve-closing position, causing the valve to close abruptly. With the intention of preventing such abrupt closure, it has been suggested that pivoting of the valve plate is counteracted by means of a spring device the effect of which increases gradually with the increase in the closing moment. Such an arrangement, however, is highly unreliable, and the spring constant of the said device changes with use, until, eventually, the valve plate will again begin to snap closed, resulting in a harsh sound in the ventilation system and disturbance of the air flow regulation.

In an attempt to over come this disadvantage, the valve plate has been provided with a tongue which lies in the air flow and which increases the closing moment when the valve is open and successively decreases the closing moment as the valve plate moves towards its closing position. One such tongue arrangement described and illustrated in Swedish Patent Specification No. 302 677 functions splendidly, but is expensive to manufacture and the tongue must be accurately positioned with respect to the planar valve plate.

One object of the present invention is to enable a valve of the aforedescribed kind to be manufactured relatively cheaply whilst functioning as efficiently as known valves in which a guiding tongue is provided on the valve plate.

According to this invention we propose an automatic regulating valve for ventilation systems, intended to permit a substantially constant volume of air to pass therethrough per unit of time with a varying pressure difference between the air-infeed side and the air-outfeed side, the valve comprising a valve plate which is mounted on a horizontal shaft for rotation in a valve housing, and means for counteracting movement of the valve plate towards a valveclosing position, wherein that part of the valve plate located above the shaft is arranged to be swung towards the direction of air flow and towards a vertical plane as the valve plate moves to a valve-closing position, wherein the surface of the valve plate percentagewise covers a larger part of the cross-sectional area of the valve housing above a plane extending through said valve housing parallel with the shaft which plane divides the cross-sectional area into two mutually equal parts, than beneath the plane, thereby to increase the rate of air flow around that part of the valve plate located beneath the shaft and to decrease the rate of air flow around that part of the plate located above the shaft, within the closing range of the valve plate..Other features of the invention are set forth in the appendant claims.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is an axial sectional view of a known regulating valve, to illustrate the forces acting on the valve plate, Figure 2 is a view similar to Fig. 1, but illustrating a valve plate according to the invention, Figure 3 is a view of the valve arrangement illustrated in Fig. 2, seen towards the outlet end, Figure 4 is a view of the valve plate of the valve arrangement illustrated in Figs. 2 and 3, seen substantially in its valve-closing position.

Figure 5 illustrates a modified valve plate for the valve arrangement illustrated in Figs. 2 and 3, and Figures 6 and 7 illustrate further embodiments of valve plates according to the invention.

Fig. 1 illustrates in a simplified fashion the operating principle of a known regulating valve through which air is intended to flow in a direction shown by the arrow, and which is intended to permit a substantially constant amount of air to pass therethrough irrespective of the pressure drop across the valve.

Mounted on a horizontal shaft 3 in a valve housing 1 is a rotatable valve plate 2. The shaft 3 is journalled for rotation in low-friction bearing (not shown), for example ball bearings. Connected either to the shaft 3 or the plate 2 is an arm 4 which carries at one end thereof a counterweight 5. The main purpose of the counterweight 5 and the arm 4 is to produce a turning moment M2 which counteracts the closing movement of the valve plate as caused by the turning moment M1, i.e. the torque generated by the air flow through the valve.As is well known, this moment M, results from the fact that with the valve plate in the illustrated position relative to the air flow the rate of air flow V3 at the forward face of the valve plate at the upper edge portion thereof is greater than the rate of flow V4 at the forward face of the valve plate in the region of the lower edge portion thereof, and that the rate of flow V1 on the rear face of the valve plate in the vicinity of its lower edge portion is greater than the rate of flow on the rear face of the plate in the vicinity of its upper edge portion, which when using recognized references for the static air pressures can also be expressed as P3 < P4 and P, < P2.

With a given setting of the valve plate the volume of air in the passage increases with an increase in the pressure drop across the valve plate 2. When the drop in pressure increases, it causes, in turn, an increase of the turning moment M1 which causes the valve plate to rotate towards its valve-closing position. As the valve plate moves towards the valveclosing position, which is illustrated in Fig. 1 by the chain line, the counter turning-moment M2 will similarly increase in the construction illustrated in Fig. 1. As a result of edge effects the valve-closing moment M1 will increase more or less abruptly as the valve plate 2 reaches the vicinity of its closed position, while the counter moment M2 follows a sinus function.This causes the valve plate to close rapidly, said valve plate being stopped by a shoulder 1 3 or by contact with the valve of the housing 1.

The effect of the edge effect occurring in the vicinity of the valve-closing position can be eliminated by decreasing the turning moment M1 in accordance with the invention, thereby enabling a balancing effect to be obtained by means of the counter moment M2, so that the valve plate moves smoothly throughout the whole of its range of movement. The invention is based on the concept of providing. an increase in the amount of air passing the underside of the valve plate 2 proportional to the amount of air passing the overside of said plate within and in the vicinity of the closing region of the valve plate; i.e.

the rate of flow increases on the underside of the plate (the static pressure decreases) and decreases on the upper side of the plate (the static pressure increases). This in turn means that the closing moment M1 decreases as the valve plate approaches its valve-closing position, and the counteracting moment M2 can be adapted so that a weighted arm or a spring-loaded arm can produce a given air flow independently of the said drop in pressure.

The aforementioned increase in the amount of air flowing on the underside of the valve plate (with the plate having the closing direction shown in Fig. 1) can be obtained by decreasing the surface area of that part of the valve plate 2 located beneath the shaft 3.

Figs. 2, 3 and 4 illustrate a flat valve plate 2 of eiliptical configuration, the edge portions 8', 9' (Fig. 4) of which have been bent up to extend substantially at right angles to the plane of the valve plate and in the direction of flow, to form parts 8 and 9. This decrease in the area of the part of the valve plate lying beneath the shaft 3 results in a plate-closure area which decreases in relation to the plate area above the shaft 3 as the valve plate moves towards its closing position, and therewith also to a lower turning moment in the vicinity of the valve-closing position.

This reduction in the plate-closure area of the valve plate in the proximity of the valveclosing position of said plate can also be achieved by cutting away the lower pointed part of the ellipse shown in Fig. 4, or by completely removing the portions 8' and 9', instead of bending them in the manner stated.

Alternatively, the lower part of the valve plate may be provided with openings 10, 11, 12, as shown in Fig. 5, for increasing the rate of flow within the closing range of the valve plate.

A non-linear change in the through-flow gaps, i.e. the gaps defined by the inner wall of the housing 1 and the parts of the valve plate located above and below the shaft 3 may also be effected by placing said shaft beneath the centre of the valve plate 2, or by placing the bearing locations 6 and 7 above the centre of the plate 2 while retaining a centrally located rotary shaft 3. The former embodiment is illustrated in Fig. 6 which shows a circular valve plate 2' with a shaft 3' located beneath the centre of the plate, while the latter embodiment is shown in Fig. 7, in which the bearing locations 6, 7 are offset from the shaft 3.

Although the valve plate 2 has been assumed to be flat, it will be understood that it may also exhibit of single or a double curve.

The shape of the valve plate and the crosssectional shape of the duct through which the air flows are not important to the present invention, which can be equally as well applied to a valve housing of rectangular cross- section having a rectangular valve plate ar ranged therein.

Claims

1. An automatic regulating valve for ventilation systems, intended to permit a substantially constant volume of air to pass therethrough per unit of time with a varying pressure difference between the air-infeed side and the air-outfeed side, the vale comprising a valve plate which is mounted on a horizontal shaft for rotation in a valve housing, and means for counteracting movement of the valve plate towards a valve-closing position, wherein that part of the valve plate located above the shaft is arranged to be swung towards the direction of air flow and towards a vertical plane as the valve plate moves to a valve-closing position, wherein the surface of the valve- plate percentagewise covers a larger part of the cross-sectional area of the valve housing above a plane extending through said valve housing parallel with the shaft, which plane divides the cross-sectional area into two mutually equal parts, than beneath the plane, thereby to increase the rate of air flow around that part of the valve plate located beneath the shaft and to decrease the rate of air flow around that part of the plate located above the shaft, within the closing range of the valve plate.

2. A regulating valve according to claim 1, wherein the valve plate is symmetrical about the shaft.

3. A regulating valve according to claim 2, wherein the part of the valve plate located beneath the horizontal shaft has upwardly bent edge portions.

4. A regulating valve according to claim 2, wherein the part of the valve plate located beneath the horizontal shaft has one or more edge parts removed therefrom.

5. A regulating valve according to claim 2, wherein the part of the valve plate located beneath the horizontal shaft has apertures therein.

6. A regulating valve according to any one of claims 1 to 5, wherein the horizontal shaft is journalled in bearings located above the plane.

7. A regulating valve constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 7 of the accompanying drawings.