\"Point of no pressure change\"

Waylon Lowery

I am having trouble explaing to one of my plumbers why the air purger, expansion tank, and water makeup should be installed on the suction side of a circulator. When I tell them him that it is the "Point of no pressure Change", he looks at me, rolls his eyes, and says what does that mean?

He is convinced that installing the water makeup on the suction side of the pump will cause the system to overpressure because the suction pressure of the pump is less than the pressure setting on the pressure regulator. I told him that this may happen if the expansion tank is not installed with the makeup water, but if the expansion tank is installed with the makeup water it will be the "Point of No Pressure Change." Again I get a blank stare and a "What?"

Any help on explaining this is greatly appreciated.

Mark J Strawcutter

pumping away

Have him read the first part of Dan's "Pumpin Away" book.

Mark

DanHolohan

The compression tank

and the line connecting it to the system is the point of no pressure change. That's where the feeder belongs because the circulator can't cause a change in pressure at this point.

It's all in "Pumping Away." Buy him a copy. ;-)

Waylon Lowery

Referencing books

never gets to far with Joe Plumber....do you have any layman explanations....

jackchips_2

You should

not only buy him one but also one for yourself.

Dan spells things out so even I understood them, just an old, ordinary plumber who does a little heat now and then.

Waylon Lowery

All right, all right

I'm not getting any where....

Somebody please post a link to where I can buy this book....my Mastercard is ready....

John Starcher_4

Click on \"Books and More\"

Then click on "Plain English Books."

There are quite a few other good books there besides "Pumping Away" I would recommend "Just Add H2O" and "Primary Secondary Made Easy" to start with.

Starch

Mark Eatherton1

The P.O.N.P.C. in pictures...

I don't know how to make it any simpler. I've tried a thousand times, and these drawings are the simplest form I can lower it to.

Described simply, it is the ONE point in the hydronic heating system where the atmospheric pressure interconnects, and or interfaces to the hydronic side of the system. It is the ONE place that the pump has NO influence, either positive or negative...

ME

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jim sokolovic

Mark, the diagrams are nicely done...

but how does the term "atmospheric" correlate to the contained, compressed air inside the compression tank?
Is this to maintain the rational going back to the open systems?

Weezbo

recirc vs pump.

try this ...recirc are not like a well pump...if he cant understand that concept, nothing you could say would make any sence to him, except , Lunch time, coffee break and Pay day ..... maybe

Mark Eatherton

Yes...

As we roll back in time, and look at the first hot water heating systems, they were open to the atmosphere. Our new systems are no longer "open" systems, but the atmosphere still has an influence over the operation of circulators etc. As shown by the drawings, the PONPC is where the atmosphere exerts its influence on the system pressure.

I once made the statement that hydronics rule the world because the earth is 75% covered with water, to which an astute forced air student of mine stated, "Yeah, but its 100% covered by AIR!" Thats when the light bulb went off over MY head...

ME