FAQ & Tips
What is an external gear pump?

An external gear pump is a volumetric pump which has two gears meshing with each other in a close fitting housing. As the gears rotate, fluid fills the space between correspond gear teeth, and is carried from the inlet side to the outlet around the external circumference of the gears. Where the teeth mesh together, fluid cannot pass and so it is ejected through the outlet.

What considerations should be made for pump installations?

It is good practice to keep inlet lines as short and restriction free as possible, so ideally mount the pump under the reservoir. The pump can prime if mounted above the reservoir but this is less efficient and special priming procedures may be required. An appropriately sized filter should be fitted in the inlet flow path. Isolation valves installed on either side of the pump may make servicing cleaner/simpler where tanks are not drained regularly.

What chemicals can be pumped?

Our pumps are manufactured in a range of materials and it is possible to find a compatible material for most fluids. In any case given the variety of conditions and fluids it is always advisable testing the pump in the circuit, under conditions and with the fluid which will then be in operation.

Can the pumps be used for metering?

All of our pumps are positive displacement units and can be used in metering applications. Accuracy and repeatability will be dependant on the pump type used, drive/control system and the fluid. Please contact us for further information.

What drives are available?

We offer a range of different drive types including DC, Brushless DC, Integrated, AC and Stepper motors. Air driven motors are also availbale on some models.

What should be considered when designing a piping system for pumps?

Keep suction requirements to a minimum, bends are better than elbows. Keep the tank high and the pump low. Use appropriately sized piping or tubing. Use isolation dampeners to avoid vibration induced noise. Design a filter before the pump and maitain it clean.

What are the advantages of magnetic drive versus traditional shaft seals?

Magnetic couplings eliminate rotating seals and a potential source of wear and contamination, besides reducing the power consumption and increasing the life of the pump. Use magnetic couplings when seal failure could cause environmental or hygiene problems. They are also more reliable when high system pressure is involved.

How can I determine the pump input power?

Fluid-o-Tech can calculate the input power required based on your duty requirements and fluid characteristics.

What information is available regarding NPIPA and NPIPR for external gear pumps?

NPSH values depend on pump capacity and speed. Typical values are shown in the chart (*).

What noise level do the pumps emit?

Noise levels are dependant on mounting of the pumps, motor speeds/types and fluid types. There are infinite combinations. A reference value at 3 bar of differential pressure, 3000 rpm of speed, is 48 dB at 1 meter (for gear pumps).

What mounting options are available?

A number of mounting options are available depending on the motor/drive requirements, including compatibility with most standard frame sizes. Please contact Fluid-o-Tech for further information.

Can liquids containing solids be pumped?

Only through our internal gear pumps.

Can the pump be run in reverse?

Our pumps are optimised for forwards flow but can be run in both directions. However, if a bypass is installed, that will impede reverse performance.

Can the pump dry run?

Not the models with mechanical seal. Pumps with magnetic drive are more tolerant, however dry running should be minimised to avoid damage to bearing surfaces.

Does the pump self-prime?

Most of our pumps will self-prime - check data sheets for individual characteristics.

What are the operating temperatures for the pump and motor?

Most of our units will run happily to 80°C (176 °F), some up to 120 °C (248 °F). This is dependent on which model is selected. Beyond that there may be a need for special consideration of magnets, clearances, motor bearings etc... Consult factory for higher temperature applications.

What symptoms are typical indicators of an inefficient pumping system?

Noise can be a key indicator of a poor pumping system. Excessive noise - particularly on the inlet side - can suggest issues such as cavitation which can dramatically affect efficiency and life. Other indicators are excessive pressure losses through the pipeline, high power consumption by the pump, overheating and vibrations.

What are the effects of viscosity on gear pump and system performances?

Viscosity can be very good for efficiency as thicker fluids have less slip. However, depending on the viscosity, maximum speed may need to be reduced to prevent excessive loads. Thinner fluids will result in increased slip and reduced efficiency. Consult factory for details.

How can I reduce the level of extraneous noise when measuring sound levels throughout a pumping system?

Some noise must be expected. Use of vibration dampeners and isolation damperners will reduce vibration noise at locations of surface contacts. Avoid pipe vibrating against metal surfaces, or motor foot vibrating against metal surface. Plastic piping should be preferred to metal piping for reducing resonance.

What kind of general considerations should be made when evaluating the inlet piping requirements for a pump?

A pump should have fittings sized for the flow rate needed. Guidance is provided in the instruction manual. If in doubt, please contact a Fluid-o-Tech engineer.

What are some effects when a gas and liquid mixture is being carried through a gear pump?

A gas/liquid mixture will pass through the pump without any problems. The pump may appear a little noisier as the gas passes through. Also there will be a momentary change in the load on the pump which may be seen through fluctuations in the outlet pressure and power consumed by the motor.

Can the pump be speed controlled?

Positive displacement pumps deliver a flow proportional to speed. Controlling the motor speed will control the flow rate. Whilst AC motors tend to be fixed speed, most DC and brushless DC motors will offer variable speed capability.

What are the minimum and maximum speeds allowable?

Maximum speeds are stated on the data sheet for each model, however, these figures are based on water. For thicker fluids, maximum speeds will need to be reduced. There is no minimum speed although motor control and slip will be factors in determining lower levels of capability.

Do the pumps conform to ATEX?

Yes, they comply with the Directive 94/9/CE of the European Parliament and of the Council, of 23rd March 1994, related to equipments and protection devices intended to be used in potentially explosive environments.

Are the pumps FDA approved?

Pumps can be supplied in FDA compliant materials.

What level of filtration is recommended?

It is recomended to install a 10 microns filter on the inlet of the pump, whose filtrating surface is big enough to avoid pressue drop, in order to protect the pump's internal components.

What affects the life of the pump and motor?

Many factors will affect life. Key issues to consider are the number of stop/start cycles, running speed, load (pressure) and fluid contamination.

What is de-coupling? Can this be used as a safety feature?

Magnet driven pumps will decouple if the load on the pump, and the motor's torque capability, exceeds the torque capability of the magnet coupling. The torque required will be affected by pressure, and fluid viscosity. When decoupling occurs, the motor will spin freely and the pump will remain at rest. This can be used as a device to protect systems from excess pressure, however the magnet decoupling point can vary depending on various factors . NOTE: Integrated motors do not decouple.

How can we adjust flow?

With a positive displacement pump, the easiest way to adjust the flow is by adjusting motor speed. There is an almost linear relationship between speed and flow.

What is the priming capabilities of the pump?

Priming performance vary from pump to pump and are dependant on a variety of factors including fluid viscosity, pipe size, vapour pressure, speed and if the pump is wet or dry.

What is slip?

Slip is the small portion of fluid that flows back through the pump clearances in the pump and affects efficiency. Thinner fluids pass more easily through these small clearances so the pump will be less efficient with thicker or more viscous fluids.

What does a relief/bypass valve do?

A relief valve is an option that protects the pump or system from excess pressure. It is adjustable and can be set to the desired pressure. When it opens, excess fluid will be re-circulated around the pump. This can also be used to prevent decoupling in magnet driven units.

What is cavitation?

Cavitation is the formation of vapour cavities in a liquid ("bubbles" or "voids") – that are the consequence of the pipe connected to the inlet of the pump which is undersized for the flow rate of the pump. Formation of these cavities is a function of the fluid properties and physical properties of the pumping system (available pressure, temperature, pumping speed…). Cavitation generates noise and premature wear of the pump.

How do I identify my pump?

By the label or the code laser marked on the pump itself. They both indentify the manufacturing date, the product code and the serial number (S/N). The data matrix encompasses the product code and the serial number (S/N).

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