Abstract: A positive displacement metering system measures the rate of travel of a free piston in a cylinder of known volume to determine the flow rate of a fluid out of the cylinder. The system may also measure and record the inlet and outlet pressures or the differential pressure between the fluid inlet and outlet. The control program positions a four-way valve which may function as an adjustable metering orifice in response to the measured flow rate and/or changes in the inlet and outlet pressures to achieve the desired flow rate. At the end of each stroke, the four-way valve is repositioned to reverse fluid flow through the metering cylinder. The system may revise the valve position settings for both forward and reverse strokes based on the measured time required for a full stroke of the piston within the cylinder at a certain valve position or a measured rate of movement of the free piston.

Abstract: A positive displacement metering system measures the rate of travel of a free piston in a cylinder of known volume to determine the flow rate of a fluid out of the cylinder. The system may also measure and record the inlet and outlet pressures or the differential pressure between the fluid inlet and outlet. The control program positions a four-way valve which may function as an adjustable metering orifice in response to the measured flow rate and/or changes in the inlet and outlet pressures to achieve the desired flow rate. At the end of each stroke, the four-way valve is repositioned to reverse fluid flow through the metering cylinder. The system may revise the valve position settings for both forward and reverse strokes based on the measured time required for a full stroke of the piston within the cylinder at a certain valve position or a measured rate of movement of the free piston.