How to Select the Right Internal Gear Pump?

A Gear pump is a type of rotary positive displacement pump, meaning they pump a constant amount of fluid for each revolution.

The application will dictate how a rotary gear pump is selected and designed. A better gear pump will be highly configurable with numerous options to cater for the application.

The items to consider when selecting an internal gear pump are as follows:

  • Duty Cycle
  • Flow
  • Differential pressure
  • Fluid viscosity
  • Corrosiveness
  • Abrasiveness
  • Temperature


Most rotary gear pump manufacturers have a medium-duty and heavy-duty pump line to cater for a wide variety of applications. A medium duty gear pump will generally only have one bearing and be suitable for lower pressures and more intermittent duties. The heavy-duty gear pump are to be used on higher pressure applications and/or continuous duties. The heavy-duty pumps will generally have a plain bearing behind the rotor and a ball bearing supporting the shaft.

G Series – self priming positive displacement rotary gear pumps


An internal gear pump can deliver flows in excess of 2000 litres per minute, but several factors need to be considered. Pumps need to have enough atmospheric pressure to support the desired flow. Good manufacturers will have accurate information on the Net Inlet Pressure Required. Other factors also need to be considered, such as shear sensitivity, viscosity and abrasiveness, all needing levels of speed reduction.



A rotary gear pump will have certain pressure ratings for heavy duty vs medium duty pumps and will probably have different pressure ratings for pumps with different construction materials. A better gear pump will have pressure ratings to 300psi [20.7 bar], but this will be for lubricating fluids. Fluids with low viscosities will reduce the maximum pressure a pump can produce.

The pressure will also affect seal selection. Some mechanical seals are only rated to 11 bar, whereas some cartridge seals are rated up to 40 bar. Most packing options will be rated to the pump’s maximum, but some special purpose packing may not, so this needs to be checked.

O-rings should also be considered [if available] instead of gaskets to minimise the chances of leaking.

differential pressure


The viscosity of a fluid affects many aspects of a rotary gear pump selection. For low viscosities, bronze bushings should not be used. For high viscosities, the speed of the pumps must slow down, often requiring reduction gearboxes. Some manufacturers [like Gorman-Rupp] have designed pumps with larger in-feed areas which enables them to support higher flows of viscous fluids while running at pole speeds, needing gearboxes only when viscosities are very high.

When viscosities get high, manufacturers will often recommend changing cast iron rotors to steel ones, which will have an effect on price. Other manufacturers have standardised on ductile iron rotors, which means that these pumps can transition into higher viscosity fluids with standard [less expensive] rotor material.

The viscosity also affects seal selection. For intermediate viscosities [up to 5000 cSt], positive drive mechanical seals can be used, but beyond this, double seals [up to 10,000 cSt], triple lip seals [up to 440,000 cSt] or packing [up to 440,000 cSt] need to be selected.



A Gear pump is often used to pump corrosive fluids, and most manufacturers will have a stainless steel construction option. But sealing materials are also important. Materials such as Viton®, Teflon®, Chemraz® and Kalrez® are useful materials to resist corrosion. O-ring and gasket material also needs consideration.

Corrosive pumping is easy with Gorman-Rupp Pumps


A rotary gear pump can be effectively applied to abrasive fluids. Some manufacturers have a special pump range to cater for this, inclusive of hardened internal metal components and needle bearings instead of plain ones. But there are other considerations depending on the abrasiveness of the application. Idler pins can be supplied in tungsten, bushings can be tungsten carbide coated or produced in silicon carbide. Mechanical seals should also have hard faces [such as silicon carbide].


Pumping fluids at high temperatures is quite possible with an internal gear pump, provided the manufacturer has the appropriate options. The internal gears will more than likely need to be trimmed to compensate for expansion, but other components in the pump will need to be upgraded. The bushings could be upgraded to “High-Temperature Carbon Graphite”, or “High-Temperature Silicon Carbide”, with a “High-Temperature Idler Pin, which would be suitable for temperatures up to 360oC.

Seals are also extremely important, and materials like Teflon for o-rings and high-temperature graphoil or chemraz® need to be considered.

Liquids that are successfully pumped with an internal Gear Pump include [but not limited to]:

high temperature fluids


Liquid Sugar


Brewer’s Yeast

Corn Syrup



Liquid Margarine

Vegetable Oils


Fish Solubles

Hot Oils












Ethyl Acetate




Heat Transfer

Cutting Oils




Anhydrous Ammonia


Foam Systems

Bonding Agents




Aviation Fuel


Hydraulic Fluid






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Gorman-Rupp Rotary Gear Pump Disassembly

Watch this instructional video showing how simple the maintenance activities are for Gorman-Rupp surface mounted self-priming pumps.













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Our expert team is standing by for any questions you have about how best to configure your pump system.

Our Internal Gear Pump Range:

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Ragazzini Peristaltic Pump are at the cutting edge of  “Hose Pump” design and have the features to make pumping easier. They consist of an elastomeric tube that is squeezed along its length by rollers that push the fluid contained within. This creates a gentle pumping action that doesn’t cause damage to the product. Further advantages include:

  • Handle a range of applications  including food products, abrasives, chemicals and solids
  • High performance including pressures to 15 BAR, reversible flow, and suction lifts
  • Easy maintenance including easy hose replacement and easy leak detection
  • CIP with retractable rollers
  • Greater operator safety
  • Easy access for monitoring or service
  • A variety of hose materials  to handle food, pharmaceuticals, abrasive and/or corrosive fluids

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The Gorman-Rupp Super T Series self-priming centrifugal wastewater/sewage pump has been the world benchmark for this technology since 1963 (>50 years). They have been designed for economical, trouble-free operation, with superior solids handling capability and a large inspection cover to access pump internals for service or blockage removal.

Advantages include:

  • Self-Priming pump has the ability to mount high and dry above the wet well (not in it)
  • Low cost of ownership
  • Greatly reduced OH&S issues – no more working over water/heights/cranes/heavy swinging weights
  • Surface-mounted pumps with easy access for monitoring or service
  • Advanced safety features including pressure relief valve to protect operators
  • 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

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The Gorman-Rupp G Series range of self priming positive displacement rotary gear pumps is designed to provide superior performance in the transfer of process fluids, unmatched in the industry. Available in Medium-Duty , Heavy-Duty and Extreme-Duty (abrasive service) models, gear pump materials include cast iron, cast steel and stainless steel.

G Series self priming pumps are manufactured with unique features that enable them to perform better and last longer on countless applications, providing quality and reliability that make the G Series the premier gear pump in the industry.

Advantages include:

  • An automatic idler pin lubrication system uses the pumped fluid to continuously cool and lubricate the idler pin and bush to reduce wear in this area.
  • An internal seal cavity venting system provides a continuous flow of liquid through the seal area, ensuring cooling and reducing pressure. This reduces seal face
  • load, increasing seal life.
  • A deep “end-feed” area offers superior priming performance under low inlet pressure conditions and/or high viscosity liquids.
  • Easy to service
  • Viscosities to 440,000 cSt
  • Pressures to 20.7 bar (300 psi)
  • Flows to 2200 litres per minute
  • Handle a variety of liquids , including highly viscous, high temperature and abrasive fluids
  • Widest range of sealing options in the industry
  • High strength gear material eliminates the need for special steel fittings traditionally needed for viscous applications.
  • Widest range of housing ports
  • Widest range of bushing materials

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The Gorman-Rupp Super U Series self priming dewatering and grey water pumps combines the best features of quality trash pumps in Australia with increased fuel efficiency and higher heads to pump through smaller and/or longer discharge piping systems or overcome the losses in filter systems.

These centrifugal pumps have been designed for economical, heavy duty (24/7) trouble-free operation.

Advantages include:

  • Ability to mount high and dry above the water (not in it)(to 7.6m)
  • Low cost of ownership
  • Greatly reduced OH&S issues
  • Easy access for monitoring or service
  • Advanced safety features to protect operators
  • 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
  • Any engine brand required by the customer
  • Choice of skid or trailer mounted configuration

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Ragazzini Rotho Peristaltic Pumps are the ideal choice for dosing and metering.

They consist of an elastomeric tube that is squeezed along its length by rollers that push the fluid contained within. This creates a gentle pumping action that doesn’t cause damage to the peristaltic pump.

Advantages include:

  • Handle a range of fluids including viscous products, abrasives and chemicals
  • High performance including pressures to 15 BAR, reversible flow, and suction lifts
  • Accurate metering as well as high flows (to 180m3/hour)
  • Easy maintenance including easy hose replacement and easy leak detection
  • CIP with retractable rollers
  • Greater operator safety
  • Easy access for monitoring or service
  • A variety of hose materials to handle food, pharmaceuticals, chemical, abrasive and/or corrosive fluids

Ask Our Team

The EDUR LBU multiphase pump is a multi-stage centrifugal pump with the unique capability of being able to pump a liquid/gas mixture. The centrifugal pump is constructed of either C.I./ Bz/ SS, Nodular Cast Iron, All-Bronze, Stainless Steel, or Super-Duplex Stainless Steel construction, so may be used to handle a variety of liquids.

Air, Oxygen, Carbon Dioxide and Ozone gases can be introduced into the suction line and transported and used to mix or disperse the gases. This makes the pump ideal for DAF plants, where the multiphase pumps provide the task of air saturation without the use of compressed air (no compressor, air saturation tank or associated controls).

Advantages include:

  • Liquid flows to 16 l/s
  • Gas content up to 20%
  • Cast iron/Bronze/Stainless steel, Nodular cast Iron, All-Bronze, Stainless Steel, or Super-Duplex Stainless Steel construction
  • Completely replace the “old” DAF system with a single pump

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The Lampo emergency response trailer unit is designed to speed up and simplify the deployment of emergency response equipment for municipalities, emergency services and contractors.

Advantages include:

  • Enables deployment of multiple pieces of equipment, using only one vehicle.
  • Diesel-driven power generator complete with variable frequency drive [VFD] powers a lighting tower and a rugged and reliable Gorman-Rupp pump.
  • The cleverly designed unit can light up a work area while operators set up the self-priming pump or operate numerous electric tools from the power generator.
  • The VFD allows for soft starting electrical equipment, including the pump, and can vary the speeds of these machines to suit the duty at hand. While all this is happening, the compressor can be driving air nibblers, air-operated nail guns, wrenches or tyre inflators.
  • The Lampo units also come standard with an air compressor, discharge hose reel, suction hoses and a robust mounted toolbox.

The central components of the Lampo – the generator, VFD and lighting system are manufactured by quality equipment manufacturer, Euromacchine in Italy. They are housed in an acoustically rated enclosure constructed from powder-coated galvanised steel plates.

The Lampo emergency response unit are then mounted on an Australian heavy-duty built hot-dip galvanised double axle trailer and fitted with a self-priming Gorman-Rupp trash pump.

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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.

Internal Gear Pump Articles and Projects

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