Variable Flow Outlet Valves

This invention relates to air distribution outlet valves. More particularly, it concerns a valve for providing variable amounts of air with minimum noise emission in an air conditioning system.

In known forms of air distribution valve, fluid flow may be varied by selectively changing the area of the supply duct by the introduction of some form of variable constrictor as employed in plug valves, butterfly valves, poppet and gate valves. But such constriction, whilst providing the desired mass flow by fluid pressure variation, achieves this by turbulence effect which is noise productive and, in an aircraft cockpit environment for example, distracting and undesirable. It is an object of the present invention to provide a solution to this shortcoming.

According to the present invention, there is provided a variable outlet air distribution valve, comprising relatively rotating parts and wherein the flow at the air outlet of the valve is adjusted by varying the amount of viscous drag to which the air flow is subjected as it passes through the valve from inlet to outlet, said viscous drag variation being produced by relative rotation of said valve parts which varies the length of the flow path through the valve followed by the air, whereby flow reduction at the outlet is obtained substantially without inducing noise-producing turbulence.

If the fluid flow through a supply duct can be constrained to follow a continuously increasing flow path length there will be an associated progressive reduction in pressure at the end of the flow path due to viscous pressure loss as a function of viscous drag and less turbulent pressure loss. By reducing turbulence the amount of noise generated is also reduced.

One arrangement in accordance with the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic pictorial view of a valve assembly,

FIG. 2 is a further diagrammatic pictorial view of the valve but with the inner sleeve separated from the valve body to demonstrate the construction, and

FIG. 3 is a view in section on the line 3--3 of FIG. 2.

Referring to the drawings, a valve outer body assembly 1 comprises concentric cylindrical bodies 2 and 3, the intervening space 4 being filled with a compressed porous material 5.

An end plate 6 seals off one end of the valve body 1 whilst at the outlet end a suitable seal 7 closes off the intervening space 4. An air inlet duct 8 is in communication with the intervening space 4 and, by means of a rectangular vent 9 in the inner cylindrical body 3, also provides direct air passage into the interior duct 13. The vent 9 is one of a number of constant velocity vents, the remainder in this embodiment being 10, 11, and 12. Each one is staggered radially and longitudinally relatively to its adjacent vent and all are in communcation with the intervening space 4.

A tubular outlet sleeve 14 is of outside diameter substantially corresponding to the inside diameter of the cylindrical body 3 such that the outlet sleeve 14 has a snug fit into the main body 1 as shown in FIG. 1 which will allow rotation but without significant pressure loss between the two surfaces. The outlet sleeve 14 further incorporates a knurled pressure selecting flange 15 which furthermore provides a longitudinal stop when the valve is assembled. This ensures that a stepped slot 16 in the sleeve 14 maintains correct longitudinal relationship with the vents 9-12, the length of each step 9a - 12a corresponding to the length of each vent.

With the valve assembled as shown in FIG. 1, variable air supply is available by rotation of the outlet sleeve 14. If high pressure flow is required the sleeve is rotated until that part 9a of the slot 16 is in register with the vent 9. This ensures a direct flow path from the air inlet duct 8 into the valve duct 13 and thence through the valve outlet 14. In this position the remaining vents 10, 11, and 12 are blanked off by the outlet sleeve 14. If a lower pressure supply is required this may be obtained by further rotation, each vent being associated with a particular mass flow. In this embodiment there are four pressure variables available. For example, to obtain the lowest possible pressure flow the sleeve must be rotated until that portion 12a of the slot 16 is in register with the vent 12. In this position vents 9, 10 and 11 are blanked off and inlet air under high pressure is constrained to filter through the porous material 5 before passing through the vent 12 into the outlet sleeve 14. The viscous drag effect of the porous material will reduce the pressure flow but as there will be little turbulence, noise emission of the reduced pressure flow will be minimal.

As to the porous material, the range of materials that can be employed is quite wide and the ultimate material in any particular case will be chosen to suit the environmental conditions to which the valve will be subjected. Basically, there will perhaps be two categories:

a. Metal foam or wire wool, or alternatively metallised plastic, for higher temperature operations;

b. Cheaper forms for use in cooling applications, made of polystyrene or polyurethane or similar kinds of material.

The construction of the foam has to be of the open cell kind such as is used for panscrubbers; one particular type has been named reticulated foam. In this instance the walls of the cells are removed leaving only flexible strands of material forming the cell block, so that the cells are of open construction. Such foam has recently been produced for use in fuel tanks to suppress explosions and although it can be made in many materials it is generally now known under the name reticulated foam. A successful valve according to the invention has been built using such reticulated foam compressed into the chamber 4 of the valve.