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Maximizing Pump Performance for Submersible Wastewater Pumps

Motor design is key to the performance and service life of a pump. But determining the size of the motor required to drive the pump is something people often struggle with. This is especially true of wastewater submersible pumps.

This article, written in July 2017 by Bo Gell, Americas product manager, wastewater, who has worked in Xylem’s Applied Water Systems business unit for six years. Gell has extensive experience in residential, commercial and marine pumps.  Hayes Pump specializes in Goulds Water Technology products.  Continue reading to continue learning from Bo.

It’s a common assumption that you can use motor nameplate information at face value. That applies to some, but not all nameplate data. A primary example is service factor (SF).

Generally, service factor is the measurement used to determine the peak performance at which a pump motor can operate. The National Electrical Manufacturers Association (NEMA) defines service factor simply as a multiplier that indicates the amount of additional load a motor can handle above its nameplate horsepower. The service factor industry standard for a totally enclosed motor is 1.0.

To determine the service factor horsepower of a motor, multiply the nameplate horsepower by the service factor. For example, if a 1 HP motor has a service factor of 1.5, the motor’s service factor maximum horsepower is:

(1 HP) x (1.5 SF) = 1.5 HP

However, when sizing submersible wastewater pump motors, horsepower service factor, which applies only to the motor, is not a primary consideration. While service factor can be used to handle intermittent or occasional overloads, designers cannot rely on the service factor capability to carry the load on a continuous basis. Doing so will likely result in reduced motor speed, and the reduced life and efficiency of the pump.

Designing Pump Systems for Continuous Duty

When sizing a submersible wastewater pump motor, it’s important to consider whether the pump will ever be required to operate at a flow rate higher than the design point. If, for example, the pump was allowed to operate at the end of the head capacity curve, the actual horsepower requirement may exceed the design point selected motor horsepower and overload the motor. For this reason, it is common practice to size the motor not for the design point, but for the end of the curve or maximum horsepower requirements.

In the example above, a 7.5 HP motor would adequately power the pump at a design point of 120 GPM at 150 feet; however, looking at the end of the curve, brake horsepower requirements call for a 10 HP motor.

It’s also important to note that submersible wastewater pumps follow Affinity Laws – the mathematic relationships that allow for the estimation of changes in pump performance as a result of a change in one of the basic pump parameters. If either the speed or impeller diameter of a pump changes, you can approximate the resulting performance change using the following:

Pursuing peak pump performance

Taking all of these factors into account, the NOL Horsepower (or non-overloading brake horsepower) is a more accurate criterion when it comes to sizing the motor for a submersible pump. The NOL Horsepower is the maximum power value calculated in order to handle the maximum power demanded by the pump at any point along the curve. NOL Horsepower represents the amount of real horsepower going to the pump, not just the horsepower used by the motor.

Although not typically listed as part of the operational information on the pump nameplate, NOL Horsepower is one of the key factors confirmed during pump performance testing. If motors overload at any point on the published curves during testing, listing agencies like UL and CSA will not award product certification to the motor vendor.

While the factors used to size a motor that will operate anywhere on the pump curve may not be those typically used as defined for standard NEMA motors, there are advantages. Selecting a pump/motor combination that will function under all possible operating conditions will result in higher efficiency, longer service life and uninterrupted performance — even in a continuous duty application.

 

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Chemineer announces NEW JT-2 Impeller

The NEW Chemineer JT-2 Impeller has been designed for a difficult application - blending high viscosity and non-Newtonian fluids.   The JT-2, a transitional flow impeller, is specially engineered for situations where conventional turbines have lost their efficiency due to viscous effects, but you don't yet need a close clearance impeller. The JT-2 provides up to 50% reduction in power draw for the same blending performance compared with competitive impellers.

Pump Systems Noise Prevention

Noise levels in buildings are receiving increasing attention.  There are even noise measurement applications for your phone to record decibel ratings and avoid places that may negatively impact your hearing.  Even mechanical piping systems play a role in noise prevention and this article will help you prevent noise problems while you are designing your system.

In an article written on this topic and distributed by Grundfos, Dick Luley, Project Engineer at Peerless Pump states,

"Much effort is being made by equipment manufacturers to provide quiet operating machines but the machine is only one part of a system so factors beyond the control of the machine manufacturer must be considered. As an example, a pump may be designed for quiet operation by the manufacturer by paying particular attention to the correct impeller and casing design to minimize hydraulic shock as the water passes from the vane tips of the impeller and enters the casing. Optimum velocity distribution of the water flow in the casing, proper shaft and bearing size to avoid shaft deflection, good hydraulic and dynamic balance of the rotating parts are important.

A quiet- design electric motor might be used and yet the pump could be a source of noise in the overall system. This is so because even with the best design and quality control of the components, all rotating machinery will still produce movement of parts within itself which in turn develop energy to appear as sound. No technology has been discovered to eliminate all pump noises since they are inherent in the mechanical, electrical and hydraulic characteristics of the machine. However, all is not lost because by the same attention to detail and workmanship in the total system design, the inherent energy-producing parts of the machine can be made scarcely noticeable.

Some examples:

  • The pump should be selected to operate near its best efficiency point.
  • The pump must be properly installed so as to achieve good alignment with its driver.
  • The piping system should be sized so as to have flow velocities of between 5-8 FPS. A pressure drop in the line of less than 10’ per 100’ of length will usually result in a 5-8 FPS velocity.
  • The suction and discharge piping to the pump should be carefully planned to avoid abrupt changes. Reducers and increasers are best in increments of one pipe size.
  • Avoid short radius elbows whenever possible. When they must be used install elbows 1 or more sizes larger than the system piping and use flanged increasers and reducers on either end. Avoid placing elbows directly on the suction and discharge of pumps, and upstream or downstream from valves and other fittings."

Download the full article for more on sound measurement, and recommended pump system noise prevention measures.

Download Pump Systems Noise Prevention Article

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How to Improve Pump System Performance

Want to know how to improve your pump system performance?   The U.S. Department of Energy’s Industrial Technologies Program (ITP) and the Hydraulic Institute (HI) have produced a guide called Improving Pumping System Performance: A Sourcebook for Industry.  Their other guides include: compressed air systems, fan and blower systems, motors and drives, steam systems, and process heating systems.

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Hayes Pump distributes only World leading manufacturers in each type of pumping technology, rated First or Second in their industry. Premier manufacturer product lines include Goulds, Viking Pump, Gorman-Rupp, Aurora, Moyno, John Crane, Warren Rupp, Wright Flow, Chemineer, Jesco and many more. Read on to learn more about every manufacturer Hayes represents.

Have Flow Disruptions Damaged your Pumps?

If you shut a valve on the discharge of many other electric pumps, something is bound to break.  The ABEL EM with the nil-flow control system automatically allows the pump to stop under pressure for added safety and pump protection.

How can Dosing Technology improve your Pumping Process?

There is almost no pumping process which does not use "dosing"  in some way.  Dosing technology is used for the production of chemicals and products as well as for their economical and ecologically beneficial application in manufacturing industries. A significant number of users of dosing technology are waterworks and sewage treatment plants as well as public swimming pools water conditioning. The spreading of dosing technology to increase the quality and economic efficiency of processes requires more information and training on “dosing technology“ so that optimum results can be achieved.

Lutz Jesco America has published an 80 page guide that provides detailed information on the dosing process, including drawings, tables, and detailed explanations - "A Brief Introduction to Dosing Technology".  It explains the basic principles in a simple way with special attention given to installation of fittings/accessories that improve your end results.

Guide includes:

Properties of media

  • Solid, liquid and gaseous substances
  • Viscosity
  • Solutions, suspensions, emulsions, colloids, coagulation, peptization
  • Sedimentation, flotation, decantation
  • Abrasion
  • Aggressiveness
  • Degassing
  • Flow behaviour of bulk material
  • Burning and explosion behaviour
  • Density