Self-Priming [wet] or Priming Assisted [dry]? Which is better? 

Self-priming pumps are divided into two categories. True [or wet] self-priming pumps and those that use an external priming system. These are called “priming assisted”, “auto-prime”, “vacuum prime” or “dry prime” pumps. Choosing which is better is very dependent on the application.

Dry Pumps

Standard centrifugal pumps are used here, which cannot create their own vacuum. These pumps rely on several “external” components to create the required vacuum in the suction line to prime the pump. They need:-

  1. A vacuum source. This can be a dedicated vacuum pump, a diaphragm pump, or a compressor/venturi system. These components are usually situated near the pump shaft so that this shaft can be used to run drive belts to the vacuum pump or compressor.
  2. An air separation chamber [or “priming hopper”]. This is mounted on the suction side of the pump immediately prior to the pump inlet. The vacuum created is “pulled” through this device to access the suction line. It comprises a cannister with a float inside. As the water rises in the suction line, it enters the priming hopper, raising the float, and through a series of linkages, closes [seals] the chamber to prevent water entering the priming devices.
  3. A non-return valve. This is positioned immediately after the pump.

This diagram shows the flow of air [and water] through the priming system of a “Dry Prime” pump.

Advantages of a Dry Prime pump

  • Because these pumps use an external priming source, a very wide range of centrifugal pumps can be used. Pumps with high flows or high heads or a combination of both can be utilised. Flows to in excess of 1000 litres per second can be achieved, as can pressures in excess of 200 metres.
  • Also, because they use an external vacuum source, suction lines can be long and/or large.
  • There is also a very wide range of materials available because priming systems can be retrofitted to any centrifugal pump.

Cons of the Dry Prime pump

  • The priming ability relies on the vacuum pump [or equivalent] to be functioning, including the belt drive system to be in good condition. A broken belt is a pump out of action.
  • The priming hoppers have a screen to try to prevent foreign matter from the suction line entering the hopper. If the screen is too fine, sludge-like fluids can block it, preventing the vacuum accessing the suction line. If the screen is too coarse, it can allow access to fibres and other solids [like cigarette butts and rags] which can build up inside the chamber, fouling the float.
  • The non-return valve in the system needs to seal perfectly for the pump to prime. If it does not seal perfectly, the vacuum system not only “pulls” air from the suction line, but also from the discharge line. This can cause priming times to be much greater than they should be, or can prevent priming all together.
  • Because of the many components in the system, they are more expensive than self-priming pumps.
  • They are more complicated and require higher levels of intervention.

 

Dry Prime pump Applications

These pumps are suited to a wide range of applications hydraulically. This includes high head and high flow mining and quarry applications, also for construction site dewatering and temporary sewer station bypass. But they are best when they are attended. Too many components need to be relied upon for the pumps to be applied to prime automatically at an unattended site.

Wet Prime Pumps

Wet prime, or “true” self-priming pumps do not rely on external priming systems. Instead, they are designed with an integral external priming tank [pump casing]. After the casing is filled with liquid, the pump simply uses the rotating impeller [which is immersed in the liquid] to create a low-pressure area [vacuum] at the impeller eye, which continually removes air from the suction line until the pump and suction line is completely primed.

Diagram shows water being separated from air, as air is primed and water is recirculated

All self-priming pumps are not created equal though. Wet prime pumps can also be split into two categories. “Standard” self-priming pumps and those that are “guaranteed” to re-prime after each and every priming cycle is completed.

All wet prime pumps can produce a high vacuum when their casings are completely full, but in an unattended “pump-down” application where solids are present in the pumped fluid, solids can lodge in the pump’s suction check valve at the completion of a pumping cycle, causing the suction leg to drain, which in turn causes a siphoning of the pump casing. “Standard” self-priming pumps will not retain enough liquid to “guarantee” re-priming – particularly on a high suction lift.

“Guaranteed re-primers”, like Gorman-Rupp’s Super T and Ultra V series pumps, are guaranteed to reprime to levels published on their performance curves. Because of this capability, these pumps can be relied upon to operate automatically every single time at an unattended site.

This video demonstrates the re-priming capability of Gorman-Rupp’s Super T series Pump

“Wet-primers” do have their limitations. They initially need to be filled with liquid [generally water] before they can start to prime. They also have flow limitations of approximately 300 litres per second, and pressure limitations to approximately 100 metres.

Advantages of Wet Prime pumps

  • They have a simple priming system that does not require a combination of systems to be operational to ensure priming.
  • The “re-primers” can operate reliably and automatically at unattended sites.
  • Small solids like cigarette butts don’t cause a problem with the priming system.
  • They are less expensive than prime assist pumps.

Cons of the Wet Prime pump

  • Wet prime pumps do not have the hydraulic range of dry primers.
  • They are not capable of priming suction lines as long as the dry prime pumps can manage.
  • Because they are purpose built to be self-primers, they do not have the full range materials available to dry primers.

Wet Prime Applications

Wet prime pumps can be applied to numerous fixed installations, and are also suitable for mobile plant [such as diesel drives]. Re-priming solids handling pumps can be applied to all manner of fixed installations including raw sewage pumping and pumping out of industrial wastewater pits including those found in food process, paper process, steelmaking and those requiring automatic liquid level control.

So which is better?

  • If it is an unattended fixed installation application, a wet prime re-primer is the choice.
  • If it is an application with easy access to first-fill the pump casing, and within the hydraulic limits of a wet primer, a wet primer is the choice.
  • If suction lines are long at an attended site, a dry prime would be the pick.
  • If hydraulic limitations exceed that of a wet primer, then a dry primer is the only choice.
there are many WHS issues when servicing a submersible pump
Ultra V self priming centrifugal wastewater and sewage pump

Ready to build the perfect pump system for your project? We’re standing by to help.

Back to Top

Priming Pumps:

Ask Our Team

The Gorman-Rupp engine driven pump is designed for applications which require high flow efficiency (even if heads are higher) and solids handling capability. Unlike the pressed aluminium housings with internal volutes, these Gorman-Rupp pumps are constructed of heavy duty sand cast aluminium components.

Advantages include:

  • Suction lifts to 7.6 metres
  • Petrol engine or diesel drive
  • 2”, 3” and 4” sizes available
  • Handle large solids (up to 50mm for the 4” pump)
  • Flows to 38 litres per second
  • Heads to 30 metres
  • Removable cover-plate to access pump internals for inspection and/or blockage removal

Ask Our Team

The Gorman-Rupp ES Auto-Start sewage pump stations are the same as any other self priming pump station, except they have an auxiliary combustion engine to drive one or more of the pumps in times of power outage. They are pre-engineered and factory tested packaged units with one, two or more sewage pumps. The motors, auxiliary engine/s, all the valves, interconnecting piping etc are all supplied as a package, inclusive of state-of-the-art purpose built controls and liquid level control systems.

The sewage pumps in the station can either be Gorman-Rupp’s Super T or Ultra V Series sewage pumps. Flows to 250 l/s for a single pump can be achieved, and this can be expanded when using self priming pumps, because only the suction line needs to be in the wet well [not whole pumps], so that 3 or more pumps can be utilised to deliver peak efficiencies when pumping ADWF [average dry weather flow] right through to peak wet weather flows. A variety of enclosures are available to house the pumping equipment.

Advantages include:

  • Lower civil costs/ engineering
  • Sewage pump stations are fully equipped and ready to “plug and play”
  • Lower operational costs
  • Greatly reduced OH&S issues
  • Easy access for monitoring or service
  • Intuitive control system
  • New advanced level control system keeps electrical equipment out of the wet well
  • Able to solve many application problems, including those with steep system head curves
  • All components within Gorman-Rupp packaged sewage pump stations are warranted for 5 years
  • Can work with the revolutionary Self Cleaning Sump (SCS) for a complete sustainable system

Ask Our Team

The Gorman-Rupp ES Base Mounted sewage pump stations are pre-engineered packaged units with one, two or more sewage pumps, motors, all valves, interconnecting piping and can be supplied with or without controls and liquid level control systems.

The sewage pumps in the station can either be Gorman-Rupp’s Super T or Ultra V Series sewage pumps. Flows to 250 l/s for a single pump can be achieved, and this can be expanded with self priming pumps, because only the suction line needs to be in the wet well [not whole pumps], so that 3 or more sewage pumps can be utilised. A variety of enclosures are available to house the sewage pump equipment.

Advantages include:

  • Lower civil costs/ engineering
  • Sewage pump stations are fully equipped and ready to “plug and play”
  • Lower operational costs
  • Greatly reduced OH&S issues
  • Easy access for monitoring or service
  • Intuitive control system
  • New advanced level control system keeps electrical equipment out of the wet well
  • Able to solve many application problems, including those with steep system head curves
  • All components within Gorman-Rupp packaged sewage pump stations are warranted for 5 years
  • Can work with the revolutionary Self Cleaning Sump (SCS) for a complete sustainable system

Ask Our Team

The Gorman-Rupp ES 200×200 is a low profile packaged sewage pump station with a specially designed fibreglass enclosure that is perfectly adapted to house all of the mechanical and electrical equipment for the complete station. The (two) sewage pumps in the station can either be Gorman-Rupp’s Super T or Ultra V Series sewage pumps.

The interior layout of the enclosures is designed to facilitate any service work that needs to be done on the sewape pumps or valves. Flows to 75 l/s for a single pump can be achieved, while the station sits on a footprint of 2.1m x 2.1m.

Advantages include:

  • Lower civil costs/ engineering
  • Stations are fully equipped and ready to “plug and play”
  • Lower operational costs
  • Greatly reduced OH&S issues
  • Easy access for monitoring or service
  • Intuitive control system
  • New advanced level control system keeps electrical equipment out of the wet well
  • Specially developed acoustic system keeps noise down to a whisper (43 dB(A) at 1.0m)
  • Available with several different external appearance options
  • All components within Gorman-Rupp packaged sewage pump stations are warranted for 5 years
  • Can work with the revolutionary Self Cleaning Sump (SCS) for a complete sustainable system

Download the Brochure | Ask Our Team

The Gorman-Rupp Ultra V Series is the most advanced self-priming centrifugal wastewater and sewage pump range on the market today.

They are high performance, high head, and high-efficiency pumps, designed to deliver a long and low maintenance service life, with a low cost of ownership.

Advantages include:

  • Ability to mount high and dry above the wet well [not in it]
  • Efficiencies up to 20% higher than any other solids handling self primer
  • Higher pressures (heads) (up to 300%) than any other solids handling self primer
  • Greatly improved operator safety
  • Easy access for monitoring or service
  • Improved maintenance features to greatly reduce maintenance time and costs, with removable rotating assembly
  • A variety of materials of construction to handle abrasive and/or corrosive fluids

Back to Top

Our Team is available to answer your pump query within the hour

Hydro’s experts are standing by to help you get the best pump, aerators and genuine spare parts for your specific project.

Email

or Call

(02) 9898 1800

Monday – Friday
9am – 5pm
Australia Wide

Over 88 years

Of Team Experience in Abattoir Pumping.

We bring you the technical knowledge & experience

We are leaders in Self Priming Centrifugal Wastewater Pump Technology. Hydro Innovations is the exclusive distributor of Gorman-Rupp pumps for all the municipal and industrial markets in Australia. Gorman-Rupp is one of the world’s leading manufacturers of self-priming sewage pumps and wastewater pumping equipment and has been for more than 75 years.

Holding a very large inventory of pumps and spare parts allows us to deliver industry-leading service. With over 88 years combined experience in applying, selecting and troubleshooting pumps, we are also in a good position to help design the best and most cost-effective fluid transfer systems for our customers.

Articles and Projects on Above Ground Pump Stations

Ready to build the perfect pump system for your project? We’re standing by to help.

Back to Top

Latest News from Hydro Innovations

Checkout the latest in pumping news.