Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Patent
1985-01-25
1987-01-20
Nilson, Robert G.
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
137220, 251 61, G05D 701
Patent
active
046374280
DESCRIPTION:
BRIEF SUMMARY
This invention concerns improvements in and relating to fluid flow control valves, and more especially to fluid flow control valves of the kind shown in published European Patent Specification No. 0 007 165.
In the above-mentioned European Patent Specification there is described a fluid flow control valve having a construction such that for any given pressure drop across the valve the volume of air flow to the valve in accordance with the position of the valve member follows a predetermined function. In one embodiment of the valve, the valve is corrected to take account of the so-called .beta. value of a system including a length of ducting arranged between the valve and a source of fluid at constant pressure, whereby the relationship between the position of the valve member and the volume of fluid flow through the valve is substantially linear.
Whilst the above-mentioned arrangement is suitable for the control of fluid flow from a fan or pump which is controlled to operate in such a manner that there is a predetermined pressure drop, or range of pressure drops, across the valve in the various settings of the valve member, such a valve is not able to provide a constant volume of fluid flow in conditions when, at a given setting of the valve member, the pressure drop across the valve is caused to change as a result of changes in the conditions under which the associated fluid flow control system is operating. For example, such changes in pressure drop may occur in a ventilating or air-conditioning system due to changes in the ambient pressure at the air outlet of the system as a result of opening or closing of windows in a room containing the relevant air outlet. A similar variation in pressure drop also occurs as between respective valves in different branches of an air flow system, owing to the different resistances to air flow presented by the corresponding runs of ducting downstream of the control valve. Such a variation in flow resistance may also occur in the same run of ducting, for example as a result of blockage of air filters in the system.
It would accordingly be desirable to provide a fluid flow control valve intended for use in such conditions with a self-adjusting mechanism that is responsive to changes in pressure drop across the valve in such a manner as to allow for changes in the operating conditions thereof and to maintain a constant volume of air flow through the valve.
There is already known, see for example U.S. Pat. No. 3,255,963 a form of fluid flow control valve that is intended to provide a constant volume of flow under varying conditions of supply pressure at the upstream side of the valve. Such a valve comprises a valve member that is spring-loaded in such a manner that it is movable to vary the opening of the valve in resonse to change in the fluid pressure at the upstream side of the valve member. Thus when the supply pressure on the upstream side of the valve member is significantly increased, the valve member is caused to yield against spring-loading in a direction closing the valve, with the object of maintaining a constant fluid flow. Such a valve arrangement has the disadvantage however, that the self-adjustment of the valve is dependent upon the force acting directly on the movable valve member as a result of the pressure on the upstream side of the valve. The setting of the valve is not, therefore, truly representative of the pressure drop across the valve and accurate adjustment of the valve member in such a manner as to maintain a constant fluid flow in the event of changes in ambient pressure on the downstream side of the valve is therefore impossible.
In another form of fluid flow control valve, see for example DE No. 1294254, it has been proposed to control the flow of fluid through the valve in response to the sensing of the pressure differential measured at points upstream and downstream of the valve and to control the position of the valve member accordingly. Such an arrangement uses a simple gate valve arrangement, however, and thus the corresponding turbulence
REFERENCES:
patent: 786667 (1905-04-01), Neumann
patent: 2399938 (1946-05-01), Pett
patent: 3554222 (1971-01-01), Kihara
patent: 4305418 (1981-12-01), Jensen
Nilson Robert G.
Spiro Investment A.G.
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