Manual Damages on Pumps and Systems. The Handbook for the Operation of Centrifugal Pumps

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Generally speaking, the discharge pipe size can be the same size as the pump discharge connection, you can see if this is reasonable by calculating the friction loss of the whole system. For the suction side, you can also use the same size pipe as the pump suction connection, often one size bigger is used ref.

A small pipe will initially cost less but the friction loss will be higher and the pump energy cost will be greater. If you know the cost of energy and the purchase and installation cost of the pipe you can select the pipe diameter based on a comparison of the pipe cost vs power consumption. Calculate the level of pressure of the high point in your system. The pressure may be low enough for the fluid to vaporize and create a vapor pocket which will be detrimental to the performance of the system.

The pressure at this point can be increased by installing a valve at some point past the high point and by closing this valve you can adjust the pressure at the high point. Of course, you will need to take that into account in the total head calculations of the pump.

For series pump installations make sure that the pressure rating of the pumps is adequate. This is particularly critical in the case where the system could become plugged due to an obstruction. All the pumps will reach their shut-of head and the pressure produced will be cumulative. The same applies for the pressure rating of the pipes and flanges. There is a minimum height to be respected between the free surface of the pump suction tank and the pump suction. If this height is not maintained a vortex will form at the surface and cause air to be entrained in the pump reducing the pump capacity.

Select your pump based on total head not discharge pressure and flow rate. The flow rate will depend on your maximum requirement.

Centrifugal pump system tips, do's and dont's

Total head is the amount of energy that the pump needs to deliver to account for the elevation difference and friction loss in your system ref. Pump selection starts with acquiring detail knowledge of the system. If you are just replacing an existing pump then of course there is no problem.

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If you are replacing an existing pump with problems or looking for a pump for a new application then you will need to know exactly how the systems is intended to work. The control method is important on-off, control valve, re-circulating, variable speed as it may affect your selection. Besides the system sketch, here is a pump data sheet that you can use to record some of the data. Depending on the industry or plant that you work in, you will be forced to either select a certain type of pump or manufacturer or both.

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Manufacturers are normally a very good source of information for final pump selection and you should always consult with them, do your own selection first and confirm it with the manufacturer. They can help you select the right type, model, and speed if you have all the operating conditions and if not they will rarely be able to help you.

This form will help you gather all the information pertinent to operation and selection of your pump. Aside from the normal end suction pump, vertical turbine and submersible pumps, there is a wide variety of specialized pumps that you should consider for your application if you have unusual conditions.

In the selection process, you will be trying to match your flow rate with the B. It is not always possible to match the flow rate with the B. Operating outside this range will lead to excessive vibration, recirculation and cavitation, see the next two figures. The first one from the Pump Handbook from McGraw-Hill which shows how the axial force increases with the distance in terms of percent flow from the B.

When you order your pump make sure that the motor is installed with spacer blocks so that the next largest motor frame can be installed. When air enters a pump it sometimes gets trapped in the volute, this reduces the capacity, creates vibration and noise. To remedy, shut the pump down and open the vent valve to remove the air. If the pump is excessively noisy do not automatically assume that the problem is cavitation, air in the pump creates vibration and noise. Cavitation produces a distinct noise similar to gravel in a cement mixer.

If you have never heard the sound of cavitation here's a recording of it in WAV format, courtesy of my friend Normand Chabot, water hammer specialist here in Montreal. Also see articles on entrained air on this web page: pumpworld. Viscosity is the main criteria which determines whether the application requires a centrifugal pump or a positive displacement pump. Centrifugal pumps can pump viscous fluids however the performance is adversely affected. If your fluid is over cSt centiStokes in viscosity consider using a positive displacement pump. Also see articles on viscosity on this web page: pumpworld.

Avoid running a pump in reverse direction, pump shafts have been broken this way especially if the pump is started while running backwards. The simplest solution is to install a check valve on the discharge line. What is the B. However, if a pump operates at shut off, it could overheat badly. Operation in such regions should be avoided. The performance or characteristic curve of the pump provides information on the relationship between total head and flow rate. There are three important points on this curve. The shut-off head, this is the maximum head that the pump can achieve and occurs at zero flow.


The pump will be noisy and vibrate excessively at this point. The pump will consume the least amount of power at this point. See also the pump glossary. The best efficiency point B. The pump will consume the power corresponding to its B.

How does a Centrifugal pump work ?

The maximum flow point, the pump may not operate past this point. The pump will consume the maximum amount of power at this point. Sometimes the characteristic curve will include a power consumption curve. This curve is only valid for water, if the fluid has a different density than water you cannot use this curve. However you can use the total head vs. If your fluid has a different viscosity than water you cannot use the characteristic curve without correction. Any fluid with a viscosity higher than 10 cSt will require a correction. Water at 60F has a viscosity of 1 cSt.

There are three different characteristic curve profiles for radial flow pumps. Figure 4 shows the various vane profiles that exist and the relationship between them. This tip is related to the radial vane profile which is the profile of the typical centrifugal pump.

Drooping, similar to the normal profile except at the low flow end where the head rises then drops as it gets to the shut-off head point. The drooping curve shape is to be avoided because it is possible for the pump to hunt between two operating points which both satisfy the head requirement of the system.

This is known to happen when two pumps are in parallel, when the second pump is started it may fail to get to the operating point or hunt between two points that are at equal head. Thankfully not to many pumps have this characteristic, here are a few:. A flat curve is sometimes desirable since a change in flow only causes a small change in head, for example as in a sprinkler system. As more sprinklers are turned on the head will tend to decrease but because the curve is flat the head will decrease only a small amount which means that the pressure at the sprinkler will drop only a small amount, thereby keeping the water velocity high at the sprinkler outlet.

The normal curve can be more or less steep. A steep curve can be desirable from a control point of view since a small change in flow will result in a large pressure drop. The steepness of the curve depends on the number of vanes and the specific speed. The usual advice you get is make the piping as straight, as big and short as possible. Avoid the use of filters at the pump inlet if at all possible.

Their maintenance will often be neglected and the pump will suffer from poor performance and perhaps cavitation. This will allow almost complete drainage of the tank and is especially useful in the case of fluids that can not be readily dumped to the sewers. It also provides additional submergence reducing the risk of vortex formation. Also be careful of elbows that are too close to the pump suction, see the pump glossary. If you are having trouble with a pump or want to check whether the new pump to be installed is appropriate, check the specific speed and the suction specific speed of the pump.

The specific speed provides a number which can help identify the type of pump for example radial or axial flow that is best suited for your application. The specific speed of the pump type selected see Figure 4 should be close to the specific speed calculated for your application. The suction specific speed will tell you if the suction of the pump is likely to cause problems in your application. Web appp for specific speed.

There are many different types of pumps available other than the standard end suction, submersible or vertical multi-stage pump. In this article, you will see a number of pumps that are specialized and may suit a particular need. This article discusses unusual aspects of pump systems : variation in pressure throughout the system and effect of fluid properties. To calculate the pressure anywhere in a system use this applet. Save time in the initial phase of the project and calculate power requirement prior to the final pump selection and compare the efficiency of the final pump selection with the industry average.

You will notice that efficiency increases with specific speed, this means that a pump with a higher speed rpm that meets your requirements will be smaller and more efficient and therefore cost less to operate, see item Predict the pump N. If you have an old centrifugal pump and no data from the manufacturer this chart can help you predict the NPSH required and avoid cavitation.

You will need to know the suction eye velocity which depends on the eye diameter. The pump works via a drive magnet, 'driving' the pump rotor, which is magnetically coupled to the primary shaft driven by the motor. They have no direct connection between the motor shaft and the impeller, so no gland is needed.

There is no risk of leakage, unless the casing is broken. Since the pump shaft is not supported by bearings outside the pump's housing , support inside the pump is provided by bushings. The pump size of a magnetic drive pumps can go from few Watts power to a giant 1MW.

Most centrifugal pumps are not self-priming. In other words, the pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. If the pump casing becomes filled with vapors or gases, the pump impeller becomes gas-bound and incapable of pumping. To ensure that a centrifugal pump remains primed and does not become gas-bound, most centrifugal pumps are located below the level of the source from which the pump is to take its suction.

The same effect can be gained by supplying liquid to the pump suction under pressure supplied by another pump placed in the suction line. The process of filling the pump with liquid is called priming. In normal conditions, common centrifugal pumps are unable to evacuate the air from an inlet line leading to a fluid level whose geodetic altitude is below that of the pump. Self-priming pumps have to be capable of evacuating air see Venting from the pump suction line without any external auxiliary devices.

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Centrifugal pumps with an internal suction stage such as water-jet pumps or side-channel pumps are also classified as self-priming pumps. Self-Priming centrifugal were invented in One of the first companies to market a self-priming centrifugal pump was American Marsh in Centrifugal pumps that are not designed with an internal or external self-priming stage can only start to pump the fluid after the pump has initially been primed with the fluid.

Sturdier but slower, their impellers are designed to move water, which is far denser than air, leaving them unable to operate when air is present. In self-priming centrifugal pumps with a separation chamber the fluid pumped and the entrained air bubbles are pumped into the separation chamber by the impeller action. The air escapes through the pump discharge nozzle whilst the fluid drops back down and is once more entrained by the impeller. The suction line is thus continuously evacuated.


The design required for such a self-priming feature has an adverse effect on pump efficiency. Also, the dimensions of the separating chamber are relatively large. For these reasons this solution is only adopted for small pumps, e. More frequently used types of self-priming pumps are side-channel and water-ring pumps. Another type of self-priming pump is a centrifugal pump with two casing chambers and an open impeller. This pump type operates without a foot valve and without an evacuation device on the suction side. The pump has to be primed with the fluid to be handled prior to commissioning.

Two-phase mixture is pumped until the suction line has been evacuated and the fluid level has been pushed into the front suction intake chamber by atmospheric pressure. During normal pumping operation this pump works like an ordinary centrifugal pump. From Wikipedia, the free encyclopedia. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources.

Unsourced material may be challenged and removed. Play media. Main article: magnetic coupling. Principles of Turbomachinery. Sprayer Supplies. Retrieved Technology and Culture. Centrifugal Pumps 2nd ed. Practical centrifugal pumps design, operation and maintenance 1. Oxford: Newnes. Retrieved 3 April Know and understand centrifugal pumps. Elsevier Ltd. Pump Sales Direct Blog. Hidden categories: Articles needing additional references from March All articles needing additional references Commons category link is on Wikidata Articles containing video clips.

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