pipe sizes and pump size

"can we check it through velocity and how??"

Yes; V = Q ÷ A where Q is the required volumetric flow rate and A the cross-sectional area of the pipe. V must not exceed V_max.

V_max is determined by the maximum allowable frictional loss in the pipe as determined by the Darcy-Weisbach or Hazen-Williams equations.

DVader1000

when u say v=Q/A this is an average velocity however how we can determine Vmax by using

Darcy-Weisbach equation

h=f(L/D)(V^2/2g)=f(L/D)(Q^2/(2gA^2)

where h is total head loss

V is velocity

Regards

You ask yourself how much of the total pump power has to be used against friction in the tubes and this is the head you can afford.

Be a bit logical do not expect to get all prechewed.

nick name, I know once I get the total head I can check with pump power, but now I want to know how we can get Vmax by using darcy eqn.

In the worse case by making a series of computations assuming different values for V and looking for which value you reach the limit you can accept.

If one result is under it and the other over it then you make an interpolation and a new approach. For this you can use a spread sheet with the equations and coefficients and introduce "V" as parameter.

I hope you do not expect that we do the computations for you or am I wrong?

As I said try to find a way since if you only expect support you will not develop your own skills.

Ok, thankx nick name

First, find out from your client what is the required flow and maximum allowable frictional head loss. From here, experiment around with different pipe sizes until you achieve a suitable one. Normally you should go for the smallest suitable size so as to minimize cost.

The other responders have given you the technical answers for doing the calculations. However others have asked related questions which were really directed at the reason for the difference in size between the pump suction line and the pump suction nozzle

This is my answer to that related question.

Pump Suction Piping

The question:

In every pump suction there is a reducer that i have seen. If the outlet of the tank nozzle is 8" (200nb) and the pump suction nozzle is 6" (150nb), we are using reducer in suction. Why can't we use a pump nozzle of 8" (200nb). Please explain me in detail....

Your question implies that you are concerned about the "added" cost of that reducer. Is that is the real basis behind your question? If so your question is a valid one. It is one of the many "Why" questions associated with piping.

My answer:

I will not try to give you a technical answer for this but I will try to give you an understanding of the situation.

First you do not change the pump nozzle to match the line size just to save the cost of a reducer. To change the size if the nozzle part of the pump case would be very much more expensive than the reducer.

So why the different size pump nozzle in the first place? Try to look at it this way. It is a matter of "Supply and Demand". The "Demand" relates to the pump. It is designed to move a certain amount of a specific fluid having specific design conditions. The pump is a specific size but it has that motor (or Turbine) driver providing the power that moves the fluid along.

To make the pump work properly you must guarantee the proper conditions at the inlet to the pump. This is called NPSH (Net Positive Suction Head). The suction line is included in the physical system that is the "Supply" part of this matter. The suction line is normally only a gravity driven conduit that must pass the same amount of fluid as the motor driven pump. To do this you must have a larger suction line than the pump nozzle. If you have a larger suction line then you have a "Supply" that meets the "Demand".

Like I said, this is not a highly technical answer but I hope it helps. So go ahead and add the reducer in the pump suction. But remember, in liquid pump suction lines, install the eccentric reducer with the flat side on top.

I have read the replies to your question with no little amazement. Start with the pump (presuming you have this item complete with motor). Obtain the pump curves for the pump & motor rpm. Its important to know the impellor size. Select the point along the curve where max efficiency line intersects the curve (usually at two points_ take the left most point). Note the head & flow rate. Calculate the pipe diameter using a flowrate of 2m/sec min & 5m/sec max. Now go to a pipe catalogue & choose your diameter from what is available in the range of your calcs. The pump suction pipe diameter should be based on a velocity of 1m/sec max. The head is primarily the vertical height that you wish to pump the fluid. Friction losses are primarily a function of pipeline length & calculated using the coefficient for the pipe material used. Add the two and go back to your pump curve. For the head calculated, check the flowrate .... if its not enough you need a bigger pump. KISS

We have to assume that the pump has been well designed and good selected based on good design criteria to fulfill the hydraulic operating conditions related to pressure and flow rate. And as a good design practice in designing of piping for both suction & discharge, the pipe sizes connected to pump nozzles must be grater than the size of pump nozzle itself, and this is very important to avoid any pressure drop due to friction losses in lower piping sizes when compared with friction loss in higher piping sizes.

For example for:

• Suction/dischare nozzle NPS 1": Pipe size is prefered to be NPS 1.5"

• Suction/dischare nozzle NPS 1.5": Pipe size NPS 2"

• Suction/dischare nozzle NPS 2": Pipe size NPS 3"

• Suction/dischare nozzle NPS 3": Pipe size NPS 4"

• Suction/dischare nozzle NPS 4": Pipe size NPS 6"

• and so on by increasing 2" for any size

Hi, there are software that will carry out several iterations to give you highly accurate answers.

For Piping system / Pump Sizing, try pipe flow expart

For single pipe system, u can use pipe flow wizard

Another good tool is pipeflow 3d. There are lots of Hydraulic Calculator online.

You need along with the above tech data to tell us what you are pumping. If it is say a new water system the velocity in the discharge line.

Also it sounds as if the pump and system are existing or you are checking pump calcs for a new system. If you have access to a "Crane's Flow of Fluids" or "Cameron Hydraulic Data" book or even an Old "Goulds GPM" pump catolog you will find all the information you need to get started. (Do not forget to check the NPSH!)

If the pump is part of an existing system you can take a reading of the amps the pump motor is drawing and if you have the pump curve you can tell if it has more capacity or is overloaded but that is only for that moment in time.

When I was doing a hydraulic drive installation, the salesman had a nice chart showing flow versus pressure for pipe sizes. It made it very easy to determine what size pipe to use for each component. If you can find this chart, you should be able to answer your questions, no problem. Just like pump curves, there are charts out there for just about anything you need. The trick is learning the names of the charts.

I agree, but the trick is to select the right pump, and the right pipe sizes is all about friction loss...the smalles the pipe the bigger the friction loss.there is a website where you can calculate this to perfection.

General Rule of thumb - suction velocity between 0.5 and 2 m/s. Discharge velocity between 3 and 5 m/s.

As a rule-of-thumb, in liquids:

• If the velocity is above 3ms^-1, then the pipe is too small.
• If the velocity is below 1ms^-1, then the pipe is too big.