Pump It Up

Declan P. McManus would have made a heck of a circulator salesman…

Could Elvis have possibly been writing about pump curves?

“Turn it down a little bit
or turn it down flat.
Pump it up when you don’t really need it.
Pump it up until you can feel it.”

I’d say it’s pretty clear that he was.

In light of our last few blog posts, I’d like to pose a question:

Which is the “stronger” circulator – a high-head, steep curve pump, or a low-head, flat-curve pump?

Answer: It depends on how you keep score.

European style steep-curve pumps provide higher head pressure, but lower flow rates.  American style flat-curve circulators prover higher flow rates, but lower head pressure.

Is higher head pressure “better?” Not if you don’t really need it.

Is a higher flow rate better? Not if you can’t feel it.

The “promise” of the 3-speed circulator is that it’s the one circulator that can do everything.  It’s supposed to make circulator selection easy and it’s supposed to replace 7 or 8 different models with just one.

And you know what?  On paper, it does just that.

On paper, the performance curves of the most common 3-speed circulators out there, the Grundfos 15-58 or the Taco 0015 (both steep-curve pumps), do cover nearly all the flow-and-head performance requirements you’re likely to encounter in residential hydronics.

On paper.

Problem is, we don’t install circulators on paper.

We install them on actual heating systems, in people’s basements.

As we’ve shown in recent blogs (click here, here, here and here to review), installing a European style steep-curve pump on a typical zone valve job would “work,” but not without noise issues – banging zone valves and possible velocity noise. And if programmed in “no call-back” mode (AKA – Speed 3), you also have tiny system Delta-T’s, which promotes boiler short-cycling, which reduces system-wide economy of operation.

But no one will be cold.

But they will have system that’s noisy and nowhere near as efficient as promised.

By the same token, installing a flat curve pump, such as a Taco 007, in a panel radiator/TRV job may present other issues.  If there’s more head loss in the piping system than the pump head can overcome, the house may not be able to heat when it’s really cold outside.

But the system will be quiet.

Install either pump as a zone pump and it’ll work. You may very likely have noise problems with the 3-speed pump in “no call-back” mode, but no one will freeze to death.

Armed with this info, you have  a couple of fixed speed options.

#1. Always use a 3-speed high-head, low-flow, steep-curve pump – even on zone valve jobs – and figure out how to deal with the noise issues (more on this later this week).  You can’t do anything about the shrinking Delta-T.

#2. Use a 3-speed, high-head, steep-curve pump where it makes sense (panel radiator jobs, zone pumping), and use a flat-curve pump where it makes sense (zone valve jobs, zone pumping).

And if you are in an emergency situation (Friday afternoon, middle of winter, dead pump), you’ll most likely wind up using whatever pump you have on the truck.  That’s fair enough, but what kind of pump should you keep on the truck?

I would think it would depend on what kinds of systems you normally service.

More to come, so in the meantime, you better listen to the radio…

“It’s a sound salvation….”


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