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Variable Speed Pump Curve

Member Posts: 19
Hello everyone.
I have been looking at pump curves on this fine thanksgiving day because there is nothing better to do when you are full of turkey.
I think I have looked my way in to confusion.
I know how to look at a curve and plot the GPM based on the head the pump will see.
But when you look at curves for things like the Alpha2, Alpha1, Taco 1816, Taco 0015e. And the docs all say things about how they will vary speed and then their charts are all straight lines.
What I am missing here is no solid info on what GPM it will flow at or is it just some place along the line?
For example you have an Alpha2, you set it to Constant Pressure 1 which is a head of 6.
If I understand it correctly and you had the pipes to handle the flow the pump will push 14 GPM like a normal pump. Now if some sort of restriction occurred which caused the head to increase, the pump in turn would slow down the flow attempting to bring the pressure back to the 6 where as an old pump would just keep pushing but move up the curve and to the left.
In normal operation the key would be providing that restriction, smaller pipes, circuit setters, TRV's, globe valves etc.
Am I seeing that right? I find myself second guessing it.

• Member Posts: 22,685
Here you go, this explains and has good graphics to help understand the different types of ECM circulator and their applications.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 204
You have this correct. If the circ is set to constant pressure, as zones close, instead of the circ building pressure moving to the left, up a constant speed curve, it stays on the programmed flat, straight constant pressure curve.

Same for proportional except instead of a flat curve it is an inclining curve (from the left to right) intended to build pressure as flows and friction losses increase in higher head systems.

Constant speed is like a car with only two gas peddle settings - on and off. Slow the car down by pressing only the break peddle. Constant or proportional pressure uses the "gas peddle" to slow the car down.

"Auto" settings picks and sets the slope of the proportional curve, otherwise you have to do it manually.

The operating point is where the parabolic (bent) system curve intersects the straight programmed curve.

Temperature control automatically hits the operating point based on programmed vs reality (delta supply/return) or setpoint temp (can be used for boiler protection, injection or assist in keeping return temps low to help condensing boilers condense).

What kind of pie did you have? Pumpkin??
• Member Posts: 249
An interesting additional pump curve presentation to add to your list. AquaMotion AM55-FVL ECM Circulator Pump. I am not sure I really understand the odd looking (to me) curves for variable speed settings. But I just installed a bunch of them. If anyone has some insight into the curves, please share.