Patent GB-465850-A (GB)
Title: Metering valve
IPC: F16K1/52
Filed: 1936-05-04
Abstract: 465,850. Valves. BROOKES, N. E. (Consolidated Ashcroft Hancock Co.) May 4, 1936, No. 12539. [Class 135] A hand-operated metering valve in which the rate of flow is proportional to the valve lift comprises a valve member 28 having, in addition to a shut-off surface 36 co-operating with a corresponding seat, a metering plug 35 cooperable with a cylindrical passage 30 spaced below the seat, and a channel 38 in the plug whose side walls 39, 40 diverge at an angle of approximately 30‹ so as to form a trapezoidal orifice, ABCD, Fig. 13, when the valve is open the shorter constant base BC of which is 15 to 75 per cent of the longer base AD when the valve is fully open. The longer base AD varies with the position of the plug relative to a metering surface 32 defining the lower wall of a chamber 37. Figs. 5, 13 show a channel 38 having a horizontal upper wall 41 and lateral walls 39,40, inclined equally to the vertical. Such a channel has thus two diametral outlet orifices ABCD and in order that these may constitute metering orifices, the valve lift must be limited so that the combined areas of the orifices ABCD is always less than the area ADHG which constitutes the inlet port. The area ABCD is divisible into a rectangle whose area CBEF increases as the valve lift and two triangles whose combined areas ABE, CFD increase as the square of the valve lift. As in the case of a rectangular opening the effect of frictional losses is to make the rate of increase of flow fall off rapidly with increased valve lift, whilst a triangular opening due to its increasing area more than compensates for such losses, the rate of flow may be increased proportionally with the valve lift by suitable choice of the ratio b/t where b is the distance BC and t is the distance AD when the valve is fully open. This ratio depends upon the size of the valve as measured by the diameter of its seat and varies between À15 and À75 when the lift is proportional to the flow. Instead of one channel 38, the metering plug may have two such channels intersecting at right-angles. Fig. 1 shows such a form. Figs. 7, 14 show a form of the invention suitable for small valves. The channel 38 has an inclined rear wall 41<m> and the metering surface 32<a> is horizontal instead of conical as shown in Figs. 1, 5, 14. In this case, the single area a b c d in the plane of the metering surface defines the metering orifice which is arranged always to be smaller than the outlet port GFba. The orifice abcd can as before be regarded as a rectangle cdmn of constant width and two triangles adm, cmb of increasing base. The metering plug may have more than one such slanting channel. The cylindrical passage 30 and the valve seat may be provided by a member 8, Fig. 1, threaded into the web 7 separating an inlet connection 3 from an outlet connection 5 in the body 1. The lift of the valve is indicated by a frusto-conical graduated collar 18 secured on a screwed valve spindle 13 and adjacent a post 22 marked to show complete turns of the handwheel 17 and supported by a collar 23 on the bonnet 9. The valve member may be formed integrally with the spindle. Tables showing actual dimensions for valves of various sizes are given in the Specification.