Item No. Not Shown UCFC5AD Main Shaft for Series 45 & 85 Used on Stenner Peristaltic Pump Parts Stenner™s adjustable metering pump is built with three detachable components: the motor, feed rate control, and pump head. Outputs are dependent upon three factors: the rpm of the motor gears, the percentage setting on the feed rate control, and the size of the peristaltic pump tube. All Stenner metering pumps have a 3-point roller design in the pump head, which acts as a check valve to prevent back flow, siphoning, overdosing and loss of prime.The motor shaft rotates at a fixed rpm which drives the adjustable feed rate control to intermittently engage the roller assembly within the pump head. The chemical solution in the pump tube is captured between the rollers as they rotate and compress the tube. As the rollers advance, the squeezed tube section regains its original form and generates a vacuum, creating the self-priming feature that delivers a constant flow unaffected by the outlet pressure.