Self Priming Pumps: Where to use them, why to use them, and the misconceptions
Self priming centrifugal pumps are often overlooked because they are not as commonly used as either standard centrifugal pumps or submersible pumps, and not understood by many who specify pumps. They can be misapplied to pumping applications by people not properly trained in their application or who do not fully understand their applications.
WHAT IS A SELF PRIMING PUMP?
A self priming pump is like any other centrifugal pump, but it is designed with an external casing that “floods” the inner pump or volute. The casing is filled with liquid [usually the same as the liquid to be pumped] and the pump is ready to go. When the impeller rotates in the casing, a low pressure area is formed at the eye of the impeller. Because the pressure is lower than atmosphere, water is pushed up the suction pipe by atmospheric pressure, forcing all the air in the suction line into the pump. The self priming pump mixes the air with the recirculating water in the casing. The air separates from the liquid and is discharged from the casing. When all the air in the suction line has been displaced, the pump is dynamic and delivers flow like any other centrifugal pump.

WHERE TO USE THEM?
Self priming centrifugal pumps can be applied to any application that standard centrifugal pumps are applied, within their hydraulic limitations. Applications from water, fuels, effluent or “grey water”, right through to raw sewage, industrial wastewater and sewage sludge can be effectively handled by self priming centrifugal pumps. Provided they are within their hydraulic limits, and they are manufactured with the right features for their intended duty, self priming pumps can deliver the safest and most cost effective of pump solutions.

WHY USE A SELF PRIMING PUMP?
Self priming pumps are mounted above the liquid source [generally at “ground level”], so less infrastructure is required to set them up. And because they are located at ground level, they are easier to access and much easier to maintain and repair. As there is no mechanical equipment in the wet well, there is no need to open wet well lids, and there is no need for hoists or cranes [as in the case of submersible pumps], making them a much safer option for operators.

HOW TO APPLY SELF PRIMING PUMPS
Firstly, the right type of pump needs to be selected for the duty [fuel pumps for fuel applications, solids handling pumps for wastewater applications etc].
The right size pump for head and flow then needs to be selected.
Then, an NPSH calculation needs to be done to ensure there is enough atmospheric pressure to support the intended flow, and the speed of the pump needs to be fast enough to prime the pump.
Selection of the suction line size is also important. It needs to be large enough to support the desired flow, and small enough to keep priming times to a minimum. It is best to avoid long suction lines, but if there is no choice, keeping part of it full during priming cycles will help [talk to Hydro Innovations about the “P Trap” design].
WHAT ARE THE LIMITATIONS OF SELF PRIMING PUMPS?
Self priming centrifugal pumps are limited in their suction lift [usually a maximum of 7.6m]. Some claims by some that 8.0 or even 8.5 metre suction lifts are possible, are misleading. Although some pumps in Australia may be able to generate a vacuum in excess of these figures [as can Gorman Rupp pumps], they cannot physically pump on these lifts because of limitations in NPSH of the pump, the temperature of the liquid, and friction losses in the suction line.
A single pump is also limited to a flow rate of about 300 litres per second. And heads above 90 metres are also difficult to achieve for true self priming pumps.

HYDRO INNOVATIONS – SELF PRIMING PUMPS
Gorman-Rupp 10 Series
Self Priming Pump
Gorman-Rupp Super T Series
Self Priming Pump
Gorman-Rupp 80 Series
Self Priming Pump
CASE STUDIES – SELF PRIMING PUMPS IN USE
TALK TO AN EXPERT
(02) 9898 1800
Australia Wide
VIDEO SERIES ON HOW TO MAINTAIN YOUR GORMAN-RUPP SELF PRIMING PUMP
INTRODUCTION AND SAFETY
BACK COVER AND WEAR PLATE REMOVAL
SUCTION CHECK VALVE REMOVAL
ROTATING ASSEMBLY REMOVAL
CARTRIDGE SEAL REMOVAL
SHAFT AND BEARING REMOVAL
CARTRIDGE SEAL INSTALLATION
IMPELLER INSTALLATION AND ADJUSTMENT
ROTATING ASSEMBLY INSTALLATION
BACK COVER INSTALLATION
PRESSURE RELIEF VALVE MAINTENANCE
SETTING PACE CLEARANCE
TROUBLESHOOTING SELF PRIMING CENTRIFUGAL PUMPS



If the suction gauge is fluctuating and the pump is making a growling noise, the problem will be vortexing. This means that the pump is pulling air from the surface of the liquid. Often a whirlpool will form on the surface, but not always. This can be solved by lowering the suction line, increasing the diameter of the suction line inlet [suction “bell”], or lowering the off level.
If the pump won’t prime or is slow to prime, there could be a suction leak. Check this by wrapping cling wrap around each joint. Repair the joint where the cling wrap is “sucked in”. If there is no leak, the suction line may be too long or its diameter too large. These things could possibly be solved by speeding the pump up, reducing the pipe diameter or construction a “P Trap”. Talk to Hydro innovations about this.
If the pump stops or fails to deliver the desired flow, check the gauges. A high suction reading will indicate a blocked or partially blocked suction line. A high discharge gauge reading will indicate a blocked or partially blocked discharge line. If both gauges are low, the pump may need a clearances adjustment or the pump may have a blocked or partially blocked impeller.

If the pump is blocking frequently, check where the pump is operating on its curve. If it is too far left, it may not have the velocity through the pump to avoid blockages. Speed pump up. If the pump is operating at its BEP [best efficiency point], the pump may not be suited to the application. Hard to fix without changing pumps [unless the pump can be upgraded with a solids handling impeller, cutting mechanism or other form of solids handling system] or fitting a strainer to the suction line [which may only move the problem].
