Contractor/Consultant – Water Utility

 

- 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 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.

 

- What is the maximum inlet pressure?

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

 

- Can Grundfos 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 is the importance of the proper design of bypass lines?

Sufficient flow through a pump is required to ensure that adequate cooling and lubrication of the pump is maintained at all times.

Inadequate cooling and lubrication will result in overheating, bearing wear, friction between the seal faces, seal leakage, and ultimately cause premature pump failure. A bypass line should be installed if there is any possibility that the pump may operate under its minimum flow requirements. The bypass line should run from the pump vent or discharge pipe back upstream of the pump as far as practical or into a tank to allow sufficient cooling of the liquid. The liquid from the bypass line must have the opportunity to cool down before re-entering the pump in order to prevent overheating of the pump. For this reason, never run the bypass line directly back to the pump inlet.

A properly sized bypass is one that satisfies the pump's minimum flow requirement, as stated in the data booklet for each pump.
Grundfos offers bypass orifices, sized for each pump model. Please note that during periods of full demand the combined flow through the system and bypass must not exceed the maximum flow rate of the pump.

 

- 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 my 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 the Grundfos Product Center, data books and/or I&O information.

 

 

 

 

- Why is my 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.

 

- What should I do if my pump motor is exceeding full load amperage?

There are several reasons why the pump may be exceeding full load amperage:


Low supply voltage, three-phase current is imbalanced, motor is shorted or grounded, wiring or connections are faulty, viscosity or specific gravity too great, and pump is bound or worn.

All of these possibilities and their solutions are discussed in the "Troubleshooting" section of the Installation and Operating Instructions (I&O) that comes with the product.

The pump might also be undersized for the application and operating beyond its rated flow. In this case try throttling the discharge valve on the system back toward the closed position until pump motor amps are within limits. Also, in some cases it is normal for a Grundfos pump to exceed the motor's rated full load amperage.

 

 

- The overloads on my motor starter are tripping (or fuses are blowing). What’s wrong?

There are several possible reasons for tripping overloads or blowing fuses. These possibilities and their solutions are discussed in the "Troubleshooting" section of the Installation and Operating Instructions (I&O).

The pump might also be undersized for the application and operating beyond its rated flow. In this case try throttling the discharge valve on the system back toward the closed position until motor amps are within limits.

 

- Can I use a motor on my pump other than the motors offered by Grundfos?

Grundfos recommends using only the motors that we offer (with a few exceptions).

The main difference between the motors offered by Grundfos versus other motors, is that Grundfos has its motors manufactured with more robust drive-end bearings. These bearings are designed to withstand higher thrust loads that are typical of multistage and some single-stage centrifugal pumps, and the end result is that motors offered by Grundfos will most likely outlast non-Grundfos motors.

We highly recommend that you use only the motors offered by Grundfos in order to maximise the life of your motor and pump.

This is especially critical for CR pumps that require motors of 3kW or greater. It is less critical for pumps other than the CR, and for CR applications requiring a 1.5kW motor or less. However, because of the wide range of quality and materials used by other motor manufacturers, Grundfos still cautions against using alternative motors in these less critical situations.

 

- How can I use integrated thermal protection in Grundfos motors?

All three-phase GRUNDFOS MG motors of 3 kW and up incorporate a thermistor TP 211.

It is necessary to make the connection of thermistor TP 211 to the managing system only through the special relay box, which exchanges the resistance's variation to managing signal.

 

- On which value the external thermal protection has to be adjusted for Grundfos motor?

It has to be adjusted to the current value not more than specified at the nameplate of the motor.

 

- What happens in case of under-voltage? (below std. voltage - 10%)

1. Std. motor: The surface temperature will increase. The motor will be overloaded, and will cut off by means of the thermal contact or the thermal relay.

2. E-motor: The built in motor protection stops the motor, and restarts when normal conditions are available.

 

- What happens in case of over-voltage? (above std. voltage + 6%)

1. Std. motor: The surface temperature will increase. The motor/pump will turn faster and therefore the power requirement will increase. This results in increased current and the motor will cut off by means of the thermal contact or the thermal relay.

2. E-motor: The built in motor protection stops the motor, and restarts when normal conditions are available.

 

 

- 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 my 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 http://www.grundfosservice.co.uk/ or telephone 01942 263628

 

 





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