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FAQ Fluid Handling

In this section we answer frequently asked questions regarding our solutions for Fluid Handling. Is your question not listed? Have your questions not been answered sufficiently? Please feel free to contact us!

FAQ Gear pumps

What causes internal leakage in a gear pump?

Although the clearances are exceptionally minimal (range of μm) for the gear pumps that Suurmond supplies, the clearances are needed to make the pump work. Through these clearances, however, product flows back from discharge to suction side.
There is also a desired leakage of the product through the bearings to the suction side of the pump. Desired because this leakage creates a lubrication film between the shafts and the bearings.

The amount of leakage depends on the following operating conditions:

  • Viscosity                      : the lower, the more leakage.
  • Differential pressure  : the higher, the more leakage.
  • Speed                           : the lower, the more leakage.
  • Temperature               : depending on the temperature, clearances can be larger or smaller.

Gear pump backflow

How does a magnetically coupled gear pump work?

A magnetically coupled gear pump is a pump that is hermetically sealed off from the atmosphere.

From a classic perspective, a pump, including a gear pump, is equipped with at least one seal. This seal on the external drive shaft prevents the pump from leaking. Depending on the application, this seal is executed as an oil seal, socket gasket or sliding ring seal (single or double).

In the case of a magnetically coupled pump, a magnet is placed on the drive shaft. This magnet is encased with a magnetic sleeve, which is mounted on the pump.

The statically sealed (often with an O-ring) magnetic sleeve ensures that the inside of the pump - where the product is in the pump - is hermetically sealed from the outside air, the atmosphere.

To power the pump, a drive is attached to the pump (alignment-free) by means of a lantern piece or pedestal. A magnet is also placed on the output shaft of the drive. When the drive is running, the outer magnet takes the inner magnet with it and the pump is driven.

MAAG industrial gear pumps for pulseless flow with magnetic drive

Magnetic coupling for MAAG gear pumps

What are the advantages of a magnetically coupled pump?

  • Magnetically coupled pumps are hermetically sealed. Secure processes!
  • Also suitable for crystallizing, toxic, reactive liquids.
  • Low maintenance.
  • Wear parts are limited to bearings and gears.
  • High suction pressures of the pump possible.
  • Extremely high and extremely low temperatures are possible.
What are the disadvantages of magnetically coupled pumps?

  • With magnetically coupled pumps, the power to be transferred is limited and depends on the strength of the magnets.
  • The magnetic losses are converted into a slight increase in temperature of the product in the magnet. With gear pumps, however, this is very limited.
When to use a magnetically coupled pump?

  • Because magnetically coupled pumps are hermetically sealed, they are the solution for pumping products that must absolutely not be exposed to the atmosphere. This for instance due to a health hazard or possible reactions to contact with the air.
  • Magnetically coupled pumps can also be used to minimize maintenance. After all, wear parts are limited to bearings and gears.

Ask our product specialists about the options for your process!

FAQ Cavitation

What is cavitation?

Cavitation is caused by poor filling of the pump. When the flow to the pump is insufficient, the "NPSH available" (Net Positive Suction Head) will be lower than the "NPSH required".

The fluid flow will be insufficient to fill the pump and vapor bubbles on the suction side will flow into the pump. These vapor bubbles are compressed and will implode on the discharge side. These implosions cause damage to the pump parts. This will eventually damage the pump in such a way that it loses its function.

The cavitation reveals itself as a metallic noise from the pump. Cavitation will cause damage to the pump.

What are possible causes of cavitation?

There are several possible causes for a pump to cavitate:

  • The engine speed is too high
  • The suction pipe is too long
  • The resistance in the suction pipe is too high
  • The vapour pressure is too high, or the suction pressure is lower than the vapour pressure of the liquid
  • The pressure in the flow vessel is too low
Why is cavitation bad for the gear pump?

Due to the above causes, the liquid flow will be insufficient to fill the pump and vapor bubbles on the suction side will flow into the pump. These vapor bubbles are compressed and will implode on the discharge side.

These implosions cause damage to the pump parts. This will eventually damage the pump in such a way that it loses its function.

What to do after a pump has cavitated?

The pump must be inspected, and damaged parts replaced. The cause of the cavitation must be determined, and necessary actions must be taken to avoid further cavitation.

How to avoid cavitation of a pump?

To avoid cavitation of the pump, always check if the NPSHavailable > NPSHrequired and take the necessary steps to create the optimal circumstances in your installation (see above).

Check the FAQ about NPSH to find out more about NPSH!

Our Suurmond specialists will be happy to support you to find a solution for your problems with cavitation or to prevent problems due to cavitation!

FAQ NPSH

What is the NPSH of a pump?

NPSH means “Nett Positive Suction Head”; the nett pressure that remains (after deducting all the pressure losses) at the entrance of the suction side of the pump.

As the gear pumps Suurmond supplies are also used with high vacuum at suction side (especially underneath reactors and with distillation), it is very important to know the NPSH value.

What is NPSHrequired:

NPSHR is the minimum pressure required. This is the value the supplier of the pump should confirm.  For gear pumps, this value depends on the viscosity and velocity of the pumped fluid, as well as the pump speed and the design of the inlet channel of the pump.

Basically, you can say that the pressure drop between the inlet of the pump and the point where the fluid is entering the teeth of the gear pump, is equal to the NPSHrequired. To get the fluid in the rotating gears, we need some extra force (pressure).

 

The NPSH is influenced by different factors, like:

  • The higher the viscosity, the higher the NPSHrequired
  • The higher the pump speed, the higher the flow, the higher the NPSHrequired
  • The bigger the opening, the lower the velocity of the fluid in the channel, the lower the NPSHrequired
What is NPSHavailable:

NPSHA is the available NPSH in the system.

This is the value the pump user must calculate and it depends on the installation. It is the absolute pressure at the suction side of the pump available.

How to calculate NPSH available?

Classically it can be calculated with the formula:
NPSHavailable = Ptank + h – dPpiping – Pvapour.

Ptank:

The pressure in the tank/vessel/container in front of the pump

h:

The height of the liquid in the tank above the centerline of the pump

dPpiping  :

The pressure drop in the piping between the tank and the opening of the pump

Pvapor

The vapor pressure @ operating temperature of the liquid

 

Pvapor is an often-forgotten value when calculating the NPSHavailable, but the most important one.

When the absolute pressure at pump inlet is below the vapor pressure of the liquid, gas will occur and the gear pump will not function (cavitation, no lubrication, etc.)

Why is it important to know the NPSH of the pump?

If the NPSHA is lower than the NPSHR, the pump will cavitate! Cavitation may cause damage to the pump and stop the process the pump is used for.

To avoid cavitation in the pump:

NPSHavailable > NPSHrequired

For more information about cavitation, check the FAQ!

Our specialists are here to advise on the optimal solution for your process. Our engineers will design a system for you according your specifications.

Let’s talk!

Let's talk!

Suurmond BV
The Netherlands
T +31 (341) 25 49 00 

Voltweg 2
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info.nl@suurmond.com

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Suurmond BV
Belgium and Luxembourg
T +32 (3) 54 44 070

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info.be@suurmond.com

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VAT BE-0440.573.109

Suurmond UK Ltd
Great Britain & Ireland
T +44 (1386) 423 756

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Evesham, Worcester
info.uk@suurmond.com

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Suurmond (France)
France
T +33 (474) 02 66 75

Parc Millésime, bâtiment 4
119 rue Michel Aulas
69400 Limas
info.fr@suurmond.com

VAT: FR59815325303
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