What makes a pump self priming

Depending on the effectiveness of these seals created by these close-tolerance parts, a positive displacement pump is capable of venting air from its suction line to some extent. However, under dry running conditions, a pump may overheat and this can cause seal wear and pump failure. Under these conditions, vapour bubbles form and expand on the suction side of the pump.

Upon reaching the high pressure, discharge side of the pump, the bubbles collapse violently causing vibration and damage to the pumping elements. For these reasons, it is important to refer to the manufacturer before using a positive displacement pump in an application where it must self-prime and, of necessity, be run dry for any period. With centrifugal pumps , the pumping action is generated by the transfer of rotational energy from the impeller to the liquid.

There are no seals between the suction and discharge sides of the pump. This means that centrifugal pumps are ineffective with gases and are not capable of evacuating air from a suction line when the liquid level is below that of the impeller.

However, with a few modifications to the basic design, a centrifugal pump can be self-priming. The impeller and volute casing is essentially surrounded by a tank so that it can always be immersed in a liquid sufficient to get the pump started and provide the pump with lubrication and cooling — provided the time taken to prime the pump is not excessive. With appropriate bearings and seals, a centrifugal pump can tolerate dry running for a limited time but this is not recommended for extended periods.

A self-priming centrifugal pump has two phases of operation: priming mode and pumping mode. In its priming mode, the pump essentially acts as a liquid-ring pump. At the same time, it also creates a cylindrical ring of liquid on the inside of the pump casing.

This effectively forms a gas-tight seal, stopping air returning from the discharge line to the suction line. There, the air is expelled and the liquid returns under gravity to the reservoir in the pump housing. Gradually, liquid rises up the suction line as it is evacuated. This process continues until liquid replaces all the air in the suction piping and the pump.

At this stage, the normal pumping mode commences, and liquid is discharged. If a pump has not been used for a while, it is important to check for losses from the casing due to leaks or evaporation before starting it. It is possible to use compressed air, instead of a liquid charge, to prime a pump.

Compressed air is blown through a jet into a tapered tube to create a vacuum. Air from the pump casing and suction line is drawn in with the compressed air and vented. The air escapes through the pump discharge nozzle whilst the fluid drops back down and is once more entrained by the impeller.

The suction line is thus continuously evacuated. The design required for such a self-priming feature has an adverse effect on pump efficiency. Also, the dimensions of the separating chamber are relatively large.

For these reasons this solution is only adopted for small pumps, e. More frequently used types of self-priming pumps are side channel and water ring pumps. Another type of self-priming pump is a centrifugal pump with two casing chambers and an open impeller. This pump type operates without a foot valve and without an evacuation device on the suction side.

More information can be found at www. We use cookies to personalize content, to provide better marketing, and to analyze our traffic. You consent to our use of Cookies if you continue to use this website. Search Close Search Bar. Pumps, Centrifugal Pump. Self-priming pumps are a specific type of liquid pump designed to have the required liquid inside the cavity or pump body necessary to start the pumping process. This offers the potential for increased operating efficiencies in process plants where pumps are used for a variety of repeated yet intermittent operations.

Pumps are used to: Move products through process lines Pump CIP clean-in-place fluids to clean and sanitize pipes and components Transfer liquids from one storage vessel to another Empty tanks and drums. Most liquid pumps used in the sanitary processing industries are centrifugal-type pumps. Centrifugal pumps are: Simple Sturdy Relatively inexpensive Ideal for pumping water and other low viscosity fluids such as CIP solutions under circumstances where suction conditions are difficult For these types of low viscosity fluids, a V-type centrifugal pump design is often preferred, featuring a vacuum pump and positive seal that is located close to the discharge port.

Advantages of Self-Priming Centrifugal Pumps Can handle a variety of liquids Work well with slurries, corrosive liquids, and suspended solids When compared to submersible-type pumps, self-priming centrifugal pumps will continue to pump liquids even after the pump is no longer submerged in a liquid tank or vessel Ideal for frequent and intermittent pumping operations, as the steps involving pump priming on start-up are eliminated. SP Series The SP Series is a liquid ring pump from Ampco that uses compression chambers to pump, and only uses centrifugal force to seal the chambers with a liquid.

A Guide to Choosing the Right Pump for Hygienic Applications This guide is intended for engineers, production managers, or anyone concerned with proper pump selection for pharmaceutical, biotechnology, and other ultra-clean applications. Next Steps For hygienic processing applications that require the frequent yet intermittent use of liquid pumps, choosing a self-priming pump may be the best solution for ensuring efficient pump operations. Contact CSI.