PUMPS
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Posted by: smd79 ® 01/27/2005, 09:10:23 Author Profile Mail author Edit

hello, im trying to choose a pump for a water system im putting in place. so far i have determined the pressure loss of the system to be 45' assuming a flow rate of 350 gpm in 4" pipe (sch40). how do i procede further? how do i determine what pump size i should be looking at? how do i use this data on the pump charts to determine the best pump? answers to any or all of these questions will be greatly appreciated. Thank you, Shawn.

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Posted by: timmyo ® 02/21/2005, 11:26:13 Author Profile Mail author Edit

First thing before anything else, make sure that the velocity in the pipe is greater than 2 ft/s so there is no builup of deposits in the pipe and no greater than 10 ft/s so that there are not cavitation problems. I doubt that you will ever get to 10 ft/ s since your headloss is usually off the charts. From there, you have to determine which pipe size will give you adequate velocity with acceptable head loss. From there, what you need to do is make a plot of your total headloss (static head + friction losses) versus flow rate (start at 0 and go up to 600 GPM for your example). Then go to some pump manufacturers website and copy their pump curves onto your system curve. Pump curves also plot flow versus head. Where the curves meet will be the operating point. You want your operating curve to hit the middle of the pump curve. This is usually the most efficient point of the pump curve. You don't want to hit the end of the pump curve, cause then you will be taxing the limits of the pump. If you find yourself hitting the end of the curve, then go to the next size horsepower pump and you will probably hit the mark. You can use pump manufactures free software to check your work and plot your curve against their pumps. Their sales reps are always ready to help you too and will verify your work or even do it for you. One manufacturer I always worked with was Meyers pumps. They have a good calculator with curves and stuff.

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Posted by: matin ® 02/09/2005, 02:11:10 Author Profile Mail author Edit

Use software from Engineered Software "pump-flo" it handles all the pumping scenarios very nicely

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Posted by: smd79 ® 02/01/2005, 08:25:57 Author Profile Mail author Edit

thanks for all the input guy. you've been a great help. i was wondering if anyone knows a good reference chart for friction losses in fittings. what are the equivalent lengths for stainless ball valves, elbows, and tees? angain all input is greatly appreciated. Thank you Shawn.

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Posted by: khaldoun ® 01/29/2005, 05:00:12 Author Profile Mail author Edit

helo shawn; when you first study a pumping systems you should begin with two assumption the velocity of the water into the pipe and the flow rate from them you determine the pipe size from the quation V=Q/A where V(velocity m/s)- Q(flow rate m*3/s)- A(pipe size m*2) then you calculate the presure loss on the base that pressure loss=200pa/m , After that from the catalogues of pumps manufacturers you chose the appropriate pump by crossing the flow rate value with pressure loss value on the chart , if you don't get a specific point on the chart Imean on a specific curve you chose the closest curve and it's recomended to chose the one upper to your point. hope that I was able to give you the help. Khaldoun.

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Posted by: quark ® 01/28/2005, 01:38:58 Author Profile Mail author Edit

Presuming you did correct calculations for resistance at the given flowrate, you should float enquiries to various manufacturers. They will select the best fit pump for you and then you can cross check it. Your pump characteristics will be 350gpm flowrate and 45ft. head. Just check for NPSHa and compare it with NPSHr of the pump you selected. Check that your duty point falls in the best efficiency region of the selected pump. (email author) gives you wealth of information about pumps. Regards, Modified by Administrator at Fri, Jan 28, 2005, 18:32:17

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Posted by: Linksys20 ® 01/27/2005, 14:52:29 Author Profile Mail author Edit

Hello Shawn It may be best if you check out Severn Science website there experts in pumps and I'm sure they will be more than happy to help. al

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