Plast-O-Matic Series VPA is an air operated, positive displacement pump used for dispensing a fixed quantity of liquid per stroke.

Design – A single acting piston is first moved to create suction or fill cycle for the liquid chamber. Second, the piston is reversed for the pressure cycle to push the liquid out of the chamber. Air pressure is used on the other piston on the air side of the pump – a connection rod is used between the pistons. The liquid chamber is fitted with diaphragm type check valves to ensure positive sealing.

Flow Per Stroke – The amount of liquid dispense per stroke is a function of the size of the piston and the stroke length of the piston. Four sizes of pistons will produce quantities up to 7 ounces, 10 ounces, 32 ounces or 128 ounces per stroke. An adjusting bolt, located on the air side, is used to control the stroke length to allow up to 20% of the maximum. Once the pump has been calibrated for the correct stroke length, the fluid displacement per stroke is approximately ½ of 1%. Up to 10 cycles per minute can be achieved.

Control – A four-way air pilot valve (not supplied) is used to control the cycles of the pump. Control of the air pilot is not included with the pump.

Material of construction – The liquid cylinder wall is constructed of PVC or 304 stainless steel. Pistons are constructed of PVC, polypro or stainless steel. Elastomer seals for the liquid piston and check valves are Buna, Viton® , or EPDM. Teflon® cap seals are optional for the liquid piston to extend the life of the stainless cylinder walls. The air side construction is always PVC with Buna seals.

Design life – Cylinder wall life is dependent upon the abrasive nature of the liquid being pumped. Tap water tests indicate 100,000 to 300,000 cycles with PVC liquid cylinders and over 1,000,000 with stainless cylinders.

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