The STH and STQ Ratio:Matic® duplex pumps from Fluid Metering (Syosset, NY) consist of two valveless pump heads direct-coupled to a single variable-speed drive (typically a 23-frame stepper motor). Displacement of each pump head is independently adjustable, and a variety of pump head sizes can be used in combination to achieve dispensing ratios from 1:1 to 500:1. Each pump head is factory-calibrated, locked in place, and will not require recalibration in the field. Models are available that can be adjusted in the field for applications that require frequent changes in mixing ratios or dispense volumes.
The pumps feature CeramPump® valveless piston pump technology that uses one moving part — a rotating and reciprocating ceramic piston — to accomplish both pumping and valving functions. The piston and mated liner are made of dimensionally stable, sapphire-hard ceramics.