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# what determines flow rate?

Member Posts: 89
if i have a baseboard loop run with 1/2 inch copper.the max trouble free flow rate is 1 1/2 gpm,correct?the pump head for the run is ..lets say 10.the pump curve for the circ im using states it will give me 7gpm with a pump head of 10.what determines the actual flow rate going through the pipe?if i am actually getting more than 1 1/2 gpm,can i then safely put more baseboard on the loop ?
Pat

• Member Posts: 1
The pump can only run on its curve,

the only way to effect the performance of a pump is to alter the restriction in the loop. (you can trim impellers and such,but that's not generally done on small circs.)

You can add restriction to the loop, moving the pump farther left on its curve. You need to be careful about how far left you move the pump, you can risk damaging a pump by dead-heading it.

The attatched image shows a pumo curve with a system curve plotted. The pump will run at the point of intersection between the system curve and the pump curve.

I hope this information helps.
• Member Posts: 427
Flow rate ?

1. The flow rate is determined by the pump curve.
2. Angainst the piping loss. which is the pipe,fittings,valves,anything the waqter floes thru.
#. Carefully measured, and documented this can be calculated with the RadPad (The FAST way to size radiant systems!) (Sku# 207)found in Books and More on this site.
4. 1 GPM will carry 10,000 btu's per hour heat.
5. The restriction in the piping is calculated in feet of head loss.
6. This "head loss " is compared on the pump curve to find out what that circuit with that pump will provide in GPM's Then see # 4. to see if that fits what heat you need for the new loop.
Note As the pump moves more water thru 2 loops the pump will be pumping more water but with less head. The loops will need to be the exact same length and half the original flow through both, or the shorter loop will take more than its share and leave the longer loop at a loss of flow. "Balance" here comes into play. And that is a whole nuther thing. Easy way install another pump for the new circuit. As Rich says the curve is the pumps ability. and the flow will fit the curve no matter what. Be in the middle of the curve and walla! You can be under the curve but never above it. anyway bigugh
PS and by the way 4 feet per second of flow thru a pipe is just right. calculate your pipe size to handel that flow, and that flow as in #4. will determine the GPM & or the btu's per hour you need as the heat loss you calculated determines.
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