Backfield In Motion

Nothing like a little late 60′s soul to help you get your groove on…

Mel & Tim from ’69 with a cautionary tale of rule breaking and flying penalty flags.

See if that doesn’t stick in your head the rest of the day…

A couple weeks back (click here) we talked about what would happen if you used a European-style steep curve 3-speed pump on a zone valve job.  A low-flow, high-head, steep curve pump will create greater and greater pressure differentials as zone valves close, and the end result – more often than not – are noisy, banging zone valves.

Zone valves don’t like closing against the kinds of pressure differentials created by your typical Grundfos 15-58 or Taco 0015 3-speed.  You can’t argue with physics.

Mel and Tim would call that “offsides and holding…

Assuming neither you nor your customer wants to live with banging zone valves, how do you quiet them down?

Hmmm mmmm hmmm…..


Yes, you in the back…

You must add a pressure differential bypass valve, you say?

Well, that’s one way of dealing with the problem.

Unfortunately, it’s also the most expensive, most difficult and least effective way of dealing with the problem.

“But all the really smart guys in the industry say you need to have them…”

No, you don’t.

Let’s call a pressure differential bypass valve (PDBV) what it really is – it’s a band-aid for a self-inflicted wound – the wound of using the wrong pump for the zone valve job in the first place.  As we’ve stated many times here, flat curve pumps and zone valves go together like football and cheerleaders – it’s what flat curve pumps were made for.

A PDBV is a spring-loaded, pressure activated valve that allows excess pressure differential created by a circulator to bypass the system, thus quieting down banging circulators.

Essentially, all a PDBV does is turn a steep curve European-style pump into a flat curve American-style pump.  

All you need to do to is purchase and install the valve itself, plus all the associated piping, and then figure out how to set the valve so it does what you want, while trying to decipher instructions badly translated from German or Danish.

All for a freaking band-aid.

Seems like a lot of work, doesn’t it?

Or, you could simply use a flat curve American-style circulator in the first place.

As chronicled here, here, here and here, flat curve circulators such as the Taco 007 are designed for the types of zone valve jobs (and zone pumping jobs) fairly common here in the US.  Steep curve pumps, such as the Grundfos 15-58, the Taco 0015 and other 3-speed circulators, are designed for traditional European-style systems: small PEX pipe, large designed-for system Delta-T’s (30* or more) and panel radiators with thermostatic radiator valves.

I tend to cringe (or worse) when PDBV’s are touted as “necessary, standard equipment” on zone valve jobs, because “with those high head pumps, the zone valves will bang.  This is what you have to do to keep ‘em from banging.”

That’s like saying “here – buy this extra sharp knife set from me and use them to learn how to juggle.  Oh, and you’re gonna need to buy these band-aids from me, too.  You might bleed a little…”

Hydronics really is quite simple when you look at it through the proper lens.  When you use the wrong (low-flow, high-head, steep curve) pump with zone valves, the zone valves are most likely going to bang.  When you use the right (high-flow, low-head, flat curve) pump with zone valves, they won’t.

You can leave the band-aids to the knife jugglers.

Want some more early 70′s soul?  Get yer funk on with the Chairmen of The Board…

“Give me just a little more time…” 



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