Metering pumps move precise volumes of liquid in a specified time period to provide accurate flow rates. This class of pumps moves liquids in two stages: the suction stroke and the discharge stroke. During the suction stroke, liquid is pulled into the pump cavity past the inlet check valve. During the discharge stroke, the inlet valve closes; the outlet valve opens, and the liquid is pushed out. Vary the flow either by changing the stroke length or by adjusting the cycle frequency.

Described are a few types of metering pumps--bellows, diaphragm, peristaltic, piston, and syringe.

• Bellows Pumps move a bellows back and forth to displace liquid. These pumps do not require seals. Special nonclogging valves are available for abrasive or particulate applications. Bellows pumps produce a maximum pressure of 50 psi.
• Diaphragm Pumps pulse a flexible membrane to displace liquid with each stroke. These pumps require no seals, so you can pump abrasives and slurries if the valves are kept clean. Diaphragm pumps produce pressures to 5000 psi.
• Peristaltic Pumps are designed so that the only material in contact with the fluid being pumped is the tubing. This allows the fluid to not contaminate the pump and the pump to not contaminate the fluid. These pumps provide flexibility through the wide variety of tubing materials available.
• Piston Pumps use a reciprocating plunger to move liquid through the pump. These pumps require a seal to prevent leaks and are not recommended for use with abrasive fluids. Piston pumps produce pressures to 18,000 psi.
• Syringe Pumps either draw in or push out liquid through a syringe to obtain a known volume as determined by the size of the syringe. Up to ten syringes may be used on one pump. With the programmable pumps, up to eight commands may be programmed to perform a variety of functions. Syringe pumps are great for low flow, low pressure applications. With the addition of the high pressure version, much higher back pressure can be overcome.

Guide to Metering Pumps

Use the following guide to help you select the best type of metering pump for your application. The information given is intended as a general guideline and will not hold true for all pumps within a classification; check individual pump specifications for complete details. Pumps that have all PTFE/PFA wetted parts are recommended for applications involving aggressive liquids.

Effects of Specific Gravity

Specific gravity is an important factor to consider when sizing a pump. The specific gravity of your liquid can affect the output pressure of a pump--a heavier liquid requires greater force than water (or a lighter liquid) to be lifted an identical vertical height. The graph here compares the column heights needed to exert an equal pressure for liquids having different specific gravities. A 100-ft column of water (specific gravity of 1.0) exerts a pressure of 43.0 psi, while an 83-ft column of brine (a heavier liquid) and a 133-ft column of gasoline (a lighter liquid) are needed to exert the same pressure.

To know more, visit www.coleparmer.in or call Cole-Parmer application specialist at 022-67162222. 

About Cole-Parmer

With more than 50 years of experience, Cole-Parmer is a global leader in supplying fluid handling, life science, and general laboratory products, instrumentation, and equipment to the Biotech, Chemical, Academics, Environmental, Food, Industrial Manufacturing, and Print industries.

Offering a wide selection of products and instrumentation, Cole-Parmer works with R&D, pilot plant and production, specializing in providing scale-up assistance. With a mix of proprietary products and strategic partnering with leading manufacturers, Cole-Parmer's business is highly diversified across a spectrum of products, consumables, services and solutions.

(For further details: Cole-Parmer India Pvt. Ltd. Tel: +91-22-67162222 / 2253. Email: response@coleparmer.in, www.coleparmer.in)