Abstract: This compound flow meter includes a high capacity meter and a low capacity meter connected in parallel with it. The flow through the high capacity meter is controlled by a main valve subject to the pressure difference across the meter and biased closed by a spring. The flow through the low capacity meter is controlled by an auxiliary valve. Mounted on the main valve is a means responsive to the pressure difference across it and moving in the same direction as the main valve in response to that pressure difference. That pressure difference responsive means operates a piston which is aligned with the auxiliary valve, so that the operation of the auxiliary valve is determined by the sum of the movements of the main valve and the pressure difference responsive means.

Abstract: A compound liquid flow meter comprised of a main flow path incorporating a turbine meter (2,36) and a downstream valve (3,24), and a parallel auxiliary low flow path incorporating a relatively small capacity meter (8,41) and a fixed orifice (16,53) discharging into the main flow path downstream of the valve. The orifice size is selected to cooperate with the diameter and spring characteristics of the valve so that on increasing flow rates the valve begins to open at 45 to 55 percent of the capacity of the low flow meter (8,41) and on decreasing flow begins to close at the same flow rate. The valve action is smooth and does not require, or create, pressure impulses or surges. Furthermore, the balanced relationship between the orifice and the valve virtually eliminates the traditional loss of accuracy associated with the "change over" of prior art compound meters.