Silveys' . Tech Tip
December 98

Cooling, continued

This installment for the series has to do with the pipe size you are running and the amount of fluid you are running through it. We have covered most of the basics in the previous articles so lets talk about the GPM we have though our systems.

In water piping the term "head loss" is used. We can covert head loss into psi by dividing by 2.3 1. Thus if we have 10 foot of head loss per 100 feet of pipe we are looking at 4.32 psi loss in pressure. Now if you contact your local cooling tower or chiller supplier they have some charts and forms that you may be able to get that would than have the max. flow of fluid for a specific diameter pipe. The following table is one such chart and is from Conair Tempro.
Thanks for the time. More on the subject next time.

I.D. in inches
(Schedule 80 PVC) 		Max GPM
10Ft/Sec
0.5" 2
0.75" 5
1" 10
1.25" 20
1.5" 35
2" 70
2.5" 110
3" 195
4" 350
5" 600
6" 1,000
8" 1,600
[Max 10' Head Loss per 100' of pipe.]
Pressurized Systems Only


From the above chart what is going on with your system? If you look at the numbers you can see that by increasing the pipe size to the manifold from the 1" to say 1.5" allows 25 GPM more flow to that point. But more to the point if we are coming into the plant with a 4" line and we T to two 2.5" lines we have cut the GPM we are pushing from the 4" line. The other way to look at it is what is the water flow back to the tank? Are we feeding the system with 3" lines and returning with the same diameter, why not return with 4" and not have as great a pressure drop.

Basically from the chart, can you walk through your plant and see any possible problems? The other factor is how many go from the 2" line to say a 0.75" line or to a hose barb fitting that now restricts the flow to the system you are feeding? The simple factor is water or fluids will choose the path of least resistance and unless we use the tools available to us, we may over look something that is very simple. Now what is the GPM of your pump or pumps, and how is it distributed through the system? Does everything add up or not? Do you have areas of restriction?

Thanks for all the time. And a happy Holiday season to all!


PictSteven L Silvey
Sr. Technical Service
General Polymers Division
Ashland Chemical