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Cole-Parmer Technical Library

General Pump FAQs


  1. How do pumps work?

  2. Are centrifugal pumps variable speed?

  3. What exactly is a positive displacement pump?

  4. Which pumps can I run dry?

  5. What is the maximum viscosity rating for pumps?

  6. What pumps do you carry that will handle particulates?

  7. I need gentle pumping action, what do you recommend?

  8. When do you need to perform maintenance on pumps?



1. How do pumps work?

    Pumps move fluid in a variety of ways:

  1. Centrifugal Pumps - Use centrifugal force to push the fluid through the outlet.

  2. Metering Pumps - Bellows, diaphragm, peristaltic, piston, and syringe pumps are all metering pumps that pull the fluid through the inlet valve into a chamber, close the inlet valve, and then push the fluid through the outlet valve.

  3. Positive Displacement Pumps - Bellows, double-diaphragm, flexible impeller, gear, oscillating, piston, progressing cavity, rotary lobe, rotary vane, and peristaltic pumps have a fixed cavity that the fluid is pushed through by rollers, gears, or impeller. As the fluid is pushed through, it leaves a void or vacuum which pulls in more fluid.

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2. Are centrifugal pumps variable speed?

Most centrifugal pumps do not have variable speed motors. However, you can control flow rate on the discharge using a valve.

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3. What exactly is a positive displacement pump?

A positive displacement pump emits a given volume of fluid for each revolution of the motor. Bellows, double-diaphragm, flexible impeller, gear, oscillating, piston, progressing cavity, rotary lobe, rotary vane, and peristaltic pumps are all positive displacement pumps.

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4. Which pumps can I run dry?

Peristaltic, piston pumps with ceramic heads, bellows pumps, and diaphragm pumps can be run dry for any length of time. Centrifugal, rotary vane, and gear pumps should not be run dry; exceptions are if the gear or impeller is made of a self-lubricating material such as RYTON in which case the pump can be run for a few minutes while priming.

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5. What is the maximum viscosity rating for pumps?

This depends on the type of pump and the specific pump. Diaphragm pumps (especially double diaphragm pumps) and gear pumps are usually the best for viscous fluids.

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6. What pumps do you carry that will handle particulates?

Diaphragm pumps, bellows pumps and peristaltic pumps will work well. When choosing materials, consider chemical compatibility and resistance to wear. Use a pump with larger fittings so they don't clog as easily.

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7. I need gentle pumping action, what do you recommend?

A peristaltic pump, used at low speeds. You can also use a diaphragm pump, again at low speed. Centrifugal and gear pumps, which work at high speeds and have high shear rates, should be avoided.

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8. When do you need to perform maintenance on pumps?

This depends on the pump and the application. In general, diaphragms on metering pumps last about 6 to 12 months; gears on gear pumps last about 3 to 6 months; and motors usually last for years. DC motors require periodic brush replacement. It is important to monitor brush wear; normally brushes should be replaced every 6 months.

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Related Links: Printer-friendly page

Complete Selection of Centrifugal Pumps
Complete Selection of Drum and Hand Pumps
Complete Selection of Gear Pumps
Complete Selection of Ismatec Pumps
Complete Selection of Masterflex Peristaltic Pumps
Complete Selection of Metering Pumps
Complete Selection of Positive Displacement Pumps

General Pump FAQs
Guide to Liquid Pumps
Liquid Pump Installation Information
Liquid Pump Terminology
Liquid Pumps Technical Equations and Information Tables
Pump Types and Definitions

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