Patent ID: 8863773

Claim:
A fluid metering device for metering the flow of fluid comprising: a main chamber; a piston configured and oriented to reciprocate within the main chamber and to define a first and a second sub-chamber whose volumes vary inversely as a function of the position of the piston during its reciprocation; a first inlet valve configured to controllably regulate the flow of fluid into the first sub-chamber; a first outlet valve configured to controllably regulate the flow of fluid out of the first sub-chamber; a second inlet valve configured to controllably regulate the flow of fluid into the second sub-chamber; a second outlet valve configured to controllably regulate the flow of fluid out of the second sub-chamber; one or more sensors configured to provide feedback indicative of the position of the piston within the chamber; and a valve controller connected to each of the valves and configured to control each of the valves in a manner that causes fluid to flow through the each of the sub-chambers at an average rate that substantially tracks a control signal which is delivered to the valve controller, wherein the valve controller is configured to control each of the valves based on the feedback provided by the one or more sensors, wherein: the valve controller is configured to cycle between: a first phase during which the first inlet valve and the second outlet valve are open and the second inlet valve and the first outlet valve are closed; and a second phase during which the second inlet valve and the first outlet valve are open and the first inlet valve and the second outlet valve are closed; and the valve controller is configured to cause the period of the phases to be sufficient to enable: the first sub-chamber to completely fill with fluid during the first phase; and the second sub-chamber to completely fill with fluid during the second phase; and the valve controller is configured to cause fluid to flow through each of the sub-chambers at the average rate by extending the period of: the first phase after the first sub-chamber has completely filled with fluid by an amount which is based on the control signal; or the second phase after the second sub-chamber has completely filled with fluid by an amount which is based on the control signal, and wherein each of the sub-chambers and each of the controllable valves are configured to permit cementitious material to repeatedly flow through them while they are operating without causing a jam or damage to the device; and wherein each of the valves are configured to open by vibrating at least a portion of the valve and to close by not vibrating the portion of the valve.