Metering Pump Characteristics

1.

The pumping action is developed by a reciprocating piston. This recip- rocating motion develops a flow easily represented by a sine wave. Actual flow rate is determined by the following formula:Flow rate = Displacement x Cycles per unit of time.

ª’ª x Average FlowOne Complete CycleDischarge Metering PumpCentrifugalPumpFlow QPressure P AverageFlowSuctionTimePeak Flow-

2.

Unlike centrifugal pumps manufacturer, flow rate is not greatly affected by changes in discharge pressure.

3.

The metering pump flow vs. stroke character-istic curve is linear. It is not, however, necessar- ily proportional in that 50% stroke setting may not equal 50% flow. This is due to the fact that the calibration line may not pass through 0 on both axes simultaneously. By measuring flow at 2 stroke settings, plotting both points and drawing a straight line through them, other flow rates vs. stroke can be accurately predicted. The steady state accuracy of a correctly installed industrial grade metering pump is generally + 1.0% or better. Although a metering pump can generally be adjusted to pump at any flow rate between 0 and its maximum capacity, its accuracy is measured over a range determined by the pump's turndown ratio. Most metering pumps have a turndown ratio of 10:1, which simply means that the pump is within its accuracy rating anywhere between 10% and 100% of capacity. Centrac is an example of a new generation metering pump that features higher accuracy, and a greater turndown ratio of 100:1. Therefore, this design will accurately dose anywhere between 1% and 100% of capacity.

FlowRateQ 050100Point 2Q2, S2 Point 1Q1, S1 % Setting “S”Stroke Length or Driver Speed

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