Merchant/Distribution Partner

- What is/causes water hammer?

Water hammer is a pressure surge caused by a rapid change of water velocity in a piping system. Water hammer is often accompanied by a sound comparable to a hammer hitting a pipe, hence the name. In water well systems, water hammer is typically caused when

a) the check valve installed in the drop pipe nearest the pump is more than 9 m above the standing water level, or
b) the check valve installed in the drop pipe leaks while the next check valve above holds.

In both situations a partial vacuum is created in the drop pipe. On the next pump start, water moving at very high velocity fills the vacuum and strikes the closed check valve and the stationary water in the pipe above it, causing a pressure surge and hydraulic shock. This shock can split pipes, break joints and damage the pump and/or motor. When discovered, the system should be shut down and the pump installer contacted to correct the problem.


- What is the NPSHR curve and the relevance of it?

The NPSHR curve (Net Positive Suction Head Required) shows the amount of suction head for a given flow, the NPSH available at the inlet of the pump must exceed the value shown on the NPSHR curve by 0.6 m: NPSHA > NPSHR + 0.6 m for safety.



- What happens when you run a pump beyond the right-hand side of the curve?

Operating a pump beyond the right-hand side of the performance curve is another way of saying that the pump is producing more flow than it is designed for. It means the pump is undersized for what the system actually requires, and operating a pump in this way can damage both the motor and pump end.

A pump must be operated within its minimum and maximum flow limits at all times, and ideally the pump should be operated as closely as possible to the best efficiency point to ensure long life of the product and minimise energy consumption.


- What happens when you run a pump on the left-hand side of the curve?

Running the pump on the left hand side of the curve means that the pump is running at a high pressure and at a low or no flow condition.

High pressure in the pump drives down the impeller stack and increases pressure on the motor bearings. In extreme conditions this will cause failure of both the motor and pump end. If the flow is less than the pump's minimum flow requirement, the fluid in the pump may overheat and damage the pump.

A pump must be operated within its minimum and maximum flow limits at all times, and ideally the pump should be operated as close as possible to the best efficiency point to ensure long life of the product and minimize energy consumption.


- Can the pumps run dry?

Running a pump dry can damage the mechanical seal and motor.

The floats in your system must be adjusted to maintain the minimum water level required for the pump.

Always verify your application with our data booklet and the Installation & Operating instructions (I&O) before operation.


- What is the maximum inlet pressure?

Please refer to the Installation & Operating instructions (I&O) for your product.

  • What is the maximum allowable fluid temperature?

The maximum operating temperature for a sump/sewage or effluent pump is determined by whether the pump is run in continuous or intermittent operation under fully submerged conditions. Please refer to the Installation & Operating instructions (I&O) for your product.

Consult Grundfos regarding high temperature applications.


- Can Grundfos Commercial/Industrial pumps be safely operated outdoors with no weather protection?

In order to maximize the life of the motor and pump, some form of weather protection should be used.

Examples range from a simple rain shield to protect the pump from direct rain, or an insulated housing with space heaters to protect from freezing temperatures.


- What will happen if the pump is not emptied correctly in case of frost?

In the worst case the intermediate part of the pump, which includes pump foot and discharge, will burst.


- Which shaft seal do I need for an application?

Grundfos offers bellows and O-ring style mechanical shaft seals in its commercial/industrial products. The standard shaft seal in each pump has been designed and selected to meet the needs of typical water applications and some chemical applications.

However, some specialty applications may require different seal-face materials and different O-ring or bellows materials than in the standard seal. Grundfos offers a wide variety of seal-face material combinations such as carbon/tungsten carbide, tungsten carbide/tungsten carbide, carbon/ceramic, and silicon carbide/silicon carbide. O-rings are available in EPDM, FPM (FPM is similar in properties to Viton®), Chemraz, and Kalrez while the bellows material choices are limited to EPDM and FPM.

Shaft seal selection is based on several factors such as pressure, temperature, chemical compatibility, presence of abrasives, and viscosity. If you need help selecting a shaft seal for a specialty application, please contact a Grundfos Service Centre for assistance.

Viton® and Kalrez are registered trademarks of DuPont Dow Elastomers, and Chemraz is a registered trademark of Green, Tweed & Co.

For further information regarding shaft seals please see Grundfos Product Center, data books and/or I&O information.


- Why is the motor running hot?

Because of modern design and manufacturing techniques, it is typical for many of today's motors to run hotter than those in the past. In fact, it is not uncommon for the surface temperatures of some newer motors to reach as high as 90°C (194°F) while maintaining and even exceeding the life of motors made in the past.

This means that a "hot" motor is not necessarily an indication that something is wrong. However, if the motor in your pump application seems to be running uncharacteristically hot, there are several situations that may be causing this condition:

  • Electrical: Under or over voltage, unbalanced three-phase power, and a loss of insulation resistance;
  • Environmental: High ambient temperatures, lack of ventilation, and high altitudes (thin air);
  • Mechanical: Excessive cycling, too low or too high a flow rate, high rotating resistance by a damaged pump, high viscosity or specific gravity liquid, or obstruction in the pump.


- Can I run the pump with a variable frequency drive (VFD)?

Grundfos currently offers a wide variety of "E-pumps"... pumps with the Grundfos MGE integrated variable frequency drive motors.

MGE motors eliminate the higher cost of labour and materials and potential technical problems associated with stand-alone VFD installation. MGE motors also offer an impressive list of features and benefits. In addition to the E-pumps, all three-phase industrial motors offered by Grundfos are suitable for use with variable frequency drives.


- Where can I find instructions of installation and operation for a pump/device?

The Installation & Operating instructions (I&O) is enclosed in the pump/device box. They can also be located on the Grundfos Product Center.


- Where can I find troubleshooting information for a Grundfos Product?

The Installation and Operating instructions (I&O) that was supplied with your Grundfos product is an excellent resource for troubleshooting information.

The I&O explains proper installation, operation and maintenance procedures and also contains a troubleshooting section that covers common application problems.

If after you have reviewed the I&O and still need help, please go back to your original point of sale.


- How do I contact Grundfos Service?

Visit or telephone 01942 263628