Pressure reducing valves for reducing the pressure of a fluid i. e. a gas, vapour or liquid, to a desired level are well known. One such example is described in our UK Patent No. 1405850 in which fluid is passed through a plurality of concentric, spaced, apertured sleeves. Inlet fluid passes through the apertures in the sleeves and expands rapidly into the annular spaces defined between the sleeves thereby causing a reduction in pressure of the fluid.

Although the above design improved upon previously known designs in that high noise levels, violent turbulence and shock waves were significantly reduced there is still a need to reduce these further particularly in view of pending legislation on noise levels which reflects the current growing concern for the environment.

It is an object of the present invention to provide for an alternative and improved fluid pressure reduction valve.

According to the present invention there is provided a fluid pressure reduction valve comprising an inlet for high pressure fluid and an outlet for low pressure fluid, the inlet and outlet being separated by a pressure reduction member that comprises a plurality of layers of porous material defining a tortuous fluid path therethrough.

The plurality of layers of porous material preferably comprise a plurality of annular concentric sleeves each being constructed at least in part from porous material, the porosity of the material in adjacent sleeves increasing from inlet to outlet. The sleeves may be interspersed in a radial direction with annular support sleeves which are apertured to allow passage of the fluid.

The porous material may be sintered or may comprise a plurality of balls. The balls are preferably compacted together and may be of varying size.

The valve may further comprise a control member that is slidable on the inner surface of the pressure reduction member so as to control the amount of fluid pressure reduction. The sleeves may comprise alternate axial layers of porous sintered material and fluid impervious material.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which : Figure 1 is a longitudinal section of one embodiment of a fluid pressure reduction valve in accordance with the present invention ; and Figure 2 is an enlarged view of part of the valve of figure 1 ; Figure 3 is a longitudinal section of an alternative embodiment of the present invention.

Referring now to the drawings, a fluid pressure reduction valve comprises a housing 1 having a fluid inlet chamber 2 and a fluid outlet chamber 3 separated by a hollow cylindrical pressure reduction member 4.

A central cylindrical passage 5 defined by the pressure reduction member 4 is closed by a slidable plug 6 that has an elongate stem 7 extending out of the housing 1 where it is connected to any suitable actuator (not shown).

In the embodiment shown, the pressure reduction member 4 has a main body 8 with two concentric annular cavities 9 in each of which is received a concentric annular sleeve 10 comprising layers of porous sintered material 11 (e. g. ceramic or metallic) interspersed axially by ceramic or metallic washers 12. In the region of the sleeves 10 the main body 8 of the pressure reduction member 4 is penetrated by radial passages 13 that are aligned with the porous layers 11 of the sleeves 10 so that fluid may pass through the sintered material via aligned radial passages 13. The passages 13 are circular in cross section and are arranged in axially spaced circumferential rows each containing the same number of passages.

An outer of the concentric sleeves 8 contains sintered material 11 that has a greater porosity as compared to that of the inner concentric sleeve so that the porosity increases radially across the pressure reduction member 4, from inlet 2 to outlet 3.

The plug 6 is axially slidable on an inner surface 14 of the pressure reduction member 4 so as to open or close the innermost rows of radial passages 13.

In operation, a high pressure fluid enters the valve through the inlet chamber 2 where it encounters the pressure reduction member 4 and, if the plug 6 is in an open configuration (i. e. at least one row of radial passages is exposed), it passes through the aligned radial passages 13 and porous sintered layers 11. The porous sintered material serves to reduce the pressure of the fluid passing therethrough by means of a throttling process created by the tortuous paths the fluid follows through the material and the rapid expansion of the fluid as it egresses from the pressure reduction member 4. The pressure reduction takes place in two stages since the higher porosity of the sintered material in the outer sleeve serves to lower the fluid pressure further after it egresses from the inner sleeve and before it passes through the innermost radial passages 13 into the outlet chamber 3.

Fluid flow through the pressure reduction member 4 may be controlled by adjusting the axial position of the plug 6 in the passage 5 of the pressure reduction member 4 so as to shut off a desired proportion of radially innermost passages 13.

The fluid emergent from the pressure reduction member is at a relatively low velocity in view of its tortuous path through the sintered material. Accordingly, there is little turbulence and no shock waves as the fluid emerges. The resultant noise level is therefore low.

An alternative embodiment of the pressure reduction valve shown in figure 3 is of similar structure to the valve described above. Components corresponding to those shown in the design of figures 1 and 2 are designated with the same reference numerals and are not further described except in so far as they differ from their counterparts in figures 1 and 2. The sintered material is replaced by metal or ceramic balls 30 that are compacted in the annular cavities 9. Spacers 31 to form concentric annular sleeves 10 are located at vertically spaced intervals to divide the balls into layers. The balls may have varying sizes within each layer or across any particular layer from inlet to outlet. The clearances between the spherical surfaces of the balls 30 provide for a tortuous fluid flow path.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the porosity of the layers of material (sintered or groups of balls) may not only vary in a radial direction between adjacent sleeves but also in an axial direction between adjacent layers so that the axial position of the plug has greater control over the pressure reduction. However, in another modification the porosity between sleeves may not vary at all. It is also to be understood that there may be provided any number of concentric sleeves, depending on the particular application, and the passages may be of any suitable shape, number and arrangement provided there is adequate communication between the incoming fluid and the sintered material. In both embodiments a filter may be disposed at the entrance of the passage 5 to prevent foreign bodies in the fluid entering the valve.