Formula for GPM

zepfan

Is there a formula to determine pump gpm, when the pump curve is not available? Something other then a stopwatch, and a bucket? We have a extremely old pump that the manufacturer is un known. No nameplate
Thanks to all.

ratio

You can make a guess by looking at the pipe size, connected load, ΔT, etc., but aside from a true measurement, I think you're outta luck.

Post a pic, someone may recognize it.

Zman

ratio said:

You can make a guess by looking at the pipe size, connected load, ΔT, etc., but aside from a true measurement, I think you're outta luck.

Post a pic, someone may recognize it.

This is a good idea in any event. There is no saying it was sized correctly to begin with.

Ironman

If you know the btus it's carrying, and the delta T, then use the universal hydronic formula: btus / (delta T X 500) = gpm.

hot_rod

Depending on how accurately, or how badly you want to know
You can rent ultrasonic flow meters, they clamp on the outside of the pipe.
Motor HP size, rpm, diameter could get you a close estimate.

zepfan

Thanks to all. I was using the delta td x 500. And will try and get a picture

Tim_D

Do it right. Figure out the connected load, BTU's required. Once this is known you can calculate the required flow. Once you have the correct flow you will need to figure out the friction loss through the piping and heat emitters, plenty of rules of thumb and charts to help with this. Once you have the required flow and a good idea of the friction loss it is easy to select the correct circulator.

Zman

If you get to the point where you are looking for a decent SWAG and the load is unknown, plug in the GPM for the pipe size at 4ft/sec and use a delta T of 20. For example 1" copper carries 10.9 GPM at 4 ft/sec. 10.9 (gpm) x 500 (constant) x 20 (delta) =100,900 btu/hr. I have found that the majority of engineers design this way. In some cases, you can check a known part of the original design to verify the original engineer's preference and then apply the formula to the unknown portion.
http://s3.supplyhouse.com/product_category_files/11448-Flow-Rate-Chart.pdf

Henry

Do it the simple way that works. Get a B&G System Sizer dial. By turning the dial to the approximate net BTUs ( you may do a combustion test, new condensing boilers have the Delta T and combustion rate) plus the Delta T will show you the GPM. No math and I have used it in many litigations.

hot_rod

Online System Syzer

https://bellgossett.com/selection-sizing-cad-tools/system-syzer/