GB2120755A

GB2120755A - A device for throttling a media flow

Info

Publication number: GB2120755A
Application number: GB08310162A
Authority: GB
Inventors: Wolfram Toepser
Original assignee: H Krantz GmbH and Co
Current assignee: H Krantz GmbH and Co
Priority date: 1982-05-22
Filing date: 1983-04-14
Publication date: 1983-12-07
Also published as: GB2120755B; IT1163390B; GB8310162D0; IT8321195A0; NL8301005A; CH663645A5; DE3219296A1; DE3219296C2

Abstract

For throttling a media flow, a flap (3) is mounted in a housing (1). A shell or baffle (5) curved in a circular-segment configuration extends along a path described by one edge (4) of the flap (3). In the width direction the shell (5) has a parabolic bulge (6). Because of the presence of the shell designed in this way, the free cross-section of flow is so varied as a function of the flap position that the coefficient of resistance of the throttling of the media flow is distinguished by an approximately linear characteristic. Preferably two identically-designed shells (5), which are arranged in a mirror-inverted manner with regard to one another, are associated with each flap edge (4). <IMAGE>

Description

SPECIFICATION A device for throttling a media flow This invention relates to a device for throttling a media flow by means of a flap or butterfly valve which is mounted swingably or rotatably in a housing through which the media flows.

Such devices are used for regulating purposes in aero-dynamic installations. The throttle flaps or butterfly valves used do not, however, allow optimum controlling action, because their characteristics deviate too much from a linear characteristic, which is to be considered as ideal for the controlling action.

Instead, the known one-member throttle flaps have a coefficient of resistance g which extends in accordance with a very pronounced exponential function.

The problem underlying the invention is to provide a device for throttling a media flow of which the coefficient of resistance t is distinguished by a characteristic which is as near as possible linear.

Making a start from the device described at the beginning hereof, to solve this problem it is proposed that provided fixedly in the housing is at least one shell or baffle which is curved in a circular-segment configuration and the radius of curvature of which extends along a path which is described by one edge of the flap, in which the shell has, in the direction of its width, a parabolic bulge which varies the free cross-section of flow as a function of the respective throttle angle .

The cross-sectional diminution, brought about by the flap, upon enlargement of the throttle angle +, is superimposed by the reduction in cross-section, angle-dependent in accordance with the invention, by reason of at least one curved shell. The change in crosssection, resulting from this superimposition, by way of the throttle angle +, produces an almost linear resistance characteristic.

This coefficient of resistance t is calculated in accordance with the mathematical equation t kO + k, .+, in which: = dimensional coefficient of resistance; k0 = constant = coefficient of resistance with the flap fully open;

1 k, = constantl-degree \ degree I = rise of the characteristic; and f flap angle (degree).

In order to be able to use the throttle device, in accordance with the invention, with the linear characteristic of the coefficient of resistance meaningfully in aero-dynamic installations, the coefficient of resistance with the flap fully open should not be too high, so that not too much energy is nullified. Furthermore, the rise of the straight line should lie in a specific order of magnitude. The lower limit is fixed by the practical requirements for the throttle device and amounts to k1 > 0. On the other hand, with growing rise, also the sensitivity of the regulating instrument increases.

This sensitivity must, for production-technology reasons, be kept small. From this there emerges the requirement that k1 should be < 5. It is particularly meaningful to strive for a coefficient of resistance t with the flap fully open of < 5 and a rise of the straight line of 0.5'k1'1.5. These goals can be achieved with the device in accordance with the application.

Since the definition of the thus linearised characteristic of resistance intersects the original exponential characteristic of resistance with a flap angle of fG, the curved dishes are so arranged that they are no longer effective at an angle of + > +G and therefore the linear characteristic of resistance at (b = fG merges into the exponential function course. This naturally means a restriction of the regulating range to angles 0 S+C+G. A limiting angle fG of 55 0/01,175 o/o of the flap closing angle +0 is meaningful.

In accordance with a development of the invention, associated with one flap edge are two indentically-designed shells which are arranged in mirror-inverted manner relative to one another.

Finally, a development of the invention additionally provides for the fact that associated with the two edges of the flap, which is mounted for rotation about a central axis, are in each case two shells which are curved in a quarter-circle-shaped configuration.

One exemplified embodiment of the device in accordance with the invention, having a flap mounted for rotation about a central axis, is illustrated in the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view illustrating a preferred embodiment of the device of the invention: Figure 2 is a diagrammatic view showing the flap, with its two shells, of the device of Fig. 1 in elevation; Figure 3 is a diagrammatic section taken along the line ll-ll of Fig. 1; Figure 4 shows one of the shells on a scale enlarged as compared with Figs. 2 and 3; and Figure 5 shows one curve each for the coefficient of resistance as a function of the flap angle f of a conventional throttle device and a throttle device in accordance with the invention.

In Figs. 1 to 3, a throttle device comprises a flap 3 mounted for rotation in a housing 1 on a central axle 2.

Arranged along a path, described by edges 4 of the flap 3, in the housing 1, are shells or baffles 5, the radius of curvature of which is adapted to the paths of movement of the edges 4.

The shells 5 each have a parabolic bulge 6 which extends in such a way that a diminution in cross-section, brought about by the flap 3, upon enlargement of the flap angle f is superimposed by the angle-dependent re duction in cross-section by virtue of the shells 5.

As shown by Fig. 4, there emerges, by reason of this superimposition, a coefficient of resistance t with a linear characteristic (broken line) as compared with a conventional throttle device which has a pronounced exponential course (solid curve).

Claims

1. A device for throttling a media flow by means of a flap which is mounted swingably or rotatably in a housing through which the media flows, characterised in that provided fixedly in the housing is at least one shell or baffle which is curved in circular-segment configuration and the radius of curvature of which extends along a path described by one edge of the flap, in which the shell has, in the direction of its width, a parabolic bulge which varies the free cross-section of flow as a function of the respective throttle angle + of the flap.

2. A device as claimed in claim 1, characterised in that associated with one flap edge are two identically-designed shells which are arranged in mirror-inverted manner relative to one another.

3. A device as claimed in claim 1 or 2, characterised in that associated with the two edges of the flap, which is mounted for rotation about a central axis are in each case two shells which are curved in a quarter-circleshaped configuration.

4. A device for throttling a media flow substantially as hereinbefore described with reference to and as illustrated in the accom panying drawings.