Shake Your Tree

Some people even call him Maurice

‘Cause he speaks of the pompatus of love.

What in the name of Steve Miller is a “pompatus?”

So we’ve discussed why European-designed circulators have steep pump curves (click here), and why American-desiged circulators have flat curves (click here).  The performance curves for both circulators are specifically engineered for, and fit perfectly, the types of systems traditionally installed on each continent.

In Europe, that would be a parallel-piped panel radiator system with thermostatic radiator valves. This type of system requires a low-flow, high-head, steep curve pump.

In North America, it started with the old  venturi-tee or two-pipe systems, which morphed into series loop systems with fin-tube baseboard. These systems require high-flow, low-head, flat curve pumps.

But what would happen if we pulled the old switcharoo?


First, let’s look at what would happen with a flat curve circulator, like a Taco 007, installed in a typical European system:

Under design conditions, the system requires 10 GPM at 12′ of head.  Pretty clear the 007′s performance curve won’t be able to deliver.

As you know, systems always operate where the system curve intersects the pump curve.  For much of the heating season, this setup should work just fine.  However, as it gets colder out, the 007 would not be able to overcome the head loss of the piping system in order to deliver the required flow.

Two things would happen.

First – the measured supply and return Delta-T would be far greater than design – a sure sign of  underpumping.

And second – some rooms will be warm, while most others will be cold.  And you’ll have an unhappy customer.

Now, what would happen if you installed a steep curve pump in a typical American system?  We’ve touched on this before (click here, here and here for the full story), but here’s the Reader’s Digest version:

Systems always run where the system curve intersects the pump curve.  When using a “European” style pump, the system curve “backs up” the pump curve as zone valves close.  Each time another zone valve closes, the zone valve has to close against a higher and higher pressure differential, while the circulator delivers more flow than is required.

Is this a problem?  Depends on how you define “problem.”

If you define “problem” only as someone calling you on the phone screaming they don’t have heat, then you probably won’t have a problem.

You’ve met the bare minimum requirement for a passing grade.

You’ve earned a D-.

If you have a broader definition of “problem” – one that includes banging zone valves, incessant boiler short cycling, premature component failure and systems that aren’t nearly as economic to operate as promised or expected, then you have some things to think about.

A European style low-flow, high-head, steep curve circulator installed in a typical zone valve application can cause all of these problems.  An American-style high-flow, low-head, flat curve circulator won’t.

Because this is the type of application it was designed for.

Makes sense, doesn’t it?

We’ll examine this dynamic in greater detail, as well as how each circulator performs when used as a zone pump.

Gotta say Steve Miller’s tunes pre-Joker were, by and large, awesome!

“Winter’s people watching…”  

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