Air-operated piston pumps put the squeeze on viscous liquids.
By K Korane
| Direct-acting tandem cylinder pumps come in a number of variations and sizes, and are well suited for dispensing viscous fluids. |
Food packaging operations often need to precisely dispense highly viscous materials such, as peanut butter, shortening, syrups, and food batters. A great way to do it efficiently is by using positive-displacement piston pumps, such as those manufactured by Allenair Corp., Mineola, N.Y.
The direct-acting pumps can be powered by compressed air or other gases, any of various oils, or water. They can pump or transfer most any liquid, but are especially suited for accurately metering and dispensing thick, hard-to-handle food products. But they are not restricted to food applications; they can also dispense petroleum products, chemicals, etc.
How it all works
The pumps are based on a tandem-cylinder design that joins two cylinders together with a common rod and rod-end cap. This divides the pump into two parts, the drive and pump sections. Using a 4-way valve to operate the drive cylinder, the common rod moves the drive and pump pistons in unison, creating suction in the pump on the retract stroke and pressure on the extend stroke. The action is similar to that of a syringe. Two block vee seals, a backup O-ring, and a wear band minimize any liquid bypassing the piston.
The SSETP model, made of 300 series stainless steel, is typically used to dispense lard and other high-viscosity food products. It has an adjustment rod that lets users precisely vary the pump-piston position and, thus, the displacement chamber volume, with excellent repeatability.
Other versions of the positive-displacement pumps handle corrosive liquids, deionized water, lubricating oil, and other petroleum-based products.
Eight drive-cylinder valve options are available to control the pump. These include single- and double-solenoid pilot valves, and single and dual-pressure air pilots. They produce actions such as energizing the solenoid to extend and de-energizing to retract; energizing to extend and retracting automatically; and energizing one solenoid to extend and the other solenoid to retract. The same pattern holds for the all-air valves.
| This scematic shows the typical setup for a pump with a position-feedback transducer. A PLC monitors output data and controls the amount dispensed. |
An automatic reciprocating model incorporates a 4-way, double-bleed pilot valve. Built-in bleeder valves and internal cam bosses cause the unit to automatically reciprocate as soon as air pressure is applied.
Finally, the company offers two versions with 4-way manual valves. One requires the operator to both extend and retract the piston. On the other, operating the valve lever extends the normally retracted piston; a built-in spring return automatically retracts the rod when the lever is released.
Pump sizes include 112-, 2-, 212-, 3-, and 4-in. bores in user-specified strokes from 1.0 to 50 in. These provide pump displacement volumes ranging from 1.77 in.3 (0.008 gal) per in. of stroke in the 112-in. bore model to 12.56 in.3 (0.054 gal) per in. of stroke in the 4-in. bore version.
The pumps can be made in different variations, including a choice of seal and pump materials, depending on the application. Seal options for both the drive and pump cylinders include ethylene propylene, Nitrile, PTFE, and Viton. The latter two are especially suited for animal and vegetable oils.
Hall-effect and reed switches are available for end-of-stroke sensing. And units with built-in linear-displacement transducers can provide position feedback to a PLC or other controller.
Information for this story provided by Steve Santoriello of Allenair Corp. Contact the company at (516) 747-5450 or visit www.allenair.com.