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Point of no pressure change - help me understand

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Comments

  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    Steve,

    a Socratic question: For the circulator to add pressure to the tank it would also have to add water to the tank, and for it to do that, the water could only come from inside the pipe, and if that's the case, what will be left in the place where the water used to be in the pipe?
    Retired and loving it.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Air cushion, bladder less expansion tank

    This 5 foot tank is sealed, and hung between the ground floor joists, and must be original to the building, (circa 1900). Every year as part of the annual maintenance, it is drained and refilled to 12 psi. I just wonder what the difference will have been all those years from 1950 to now that it has been pumping towards instead of away.

    We do still have a gravity system with a vented expansion tank up high on a wall of the only floor. Maybe when we have paid for the new roof, gutters, and other expenses, we will convert to modern times.--NBC
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Agreements and misunderstandings...

    Chris, to avoid the potential of a misunderstanding, I copied what you originally wrote into my responses. I'm hoping that it is just semantics, but fear otherwise. You are obviously very comfortable doing what you do as it pertains to hydronic heating systems and domestic plumbing, and for the most part, it MUST work, or people wouldn't be calling you back year after year. But I just don't get a warm and fuzzy feeling that you completely understand and grasp the concept of the PONPC and its effect on wether a pump produces all positive pressure, all negative pressure (any pressure below static fill pressure ANYWHERE in the system) or half and half. You have some very "interesting" takes in your personal theories about what happens in these wonderful closed loop heating systems. Like none I've ever seen before. And really, it doesn't matter to me wether you adopt these methods of proper application or not. What good does it do for me to try and make YOUR life easier? If you're comfy doing what you do, and your customers are happy with what you are doing, then by all means, keep doing it. But I can't allow you to make a statement that the expansion tank connection should be down stream of the pump. At least not on a public forum that people come to seeking words of wisdom.



    I don't make this stuff up. It comes from dead men who are MUCH wiser than me, people with names like Carlson, Henry, Boyles and many others. All I can do is attempt to explain it in a manner that hopefully makes sense in the readers minds eye.



    Quite honestly, you remind me of a character who use to frequent this site many years ago by the name of Phrank Phrom Philly. He had (has) a special way with words that use to make me laugh so hard, he could bring me to tears. And he was quite set in his ways, and liked to poo poo certain theories. But when it came to understanding the electrical systems of ancient Philadelphia, he was unmatched. He's still around (Hey Phrank) but doesn't comment much anymore. I see traces of him here and there.



    You can do whatever you want to do, but the only word of advice I can give you (and others reading this thread) that will benefit you, is to make certain that all pumps pump away from the expansion tanks connection to the system.



    Peace brother...



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Paul48
    Paul48 Member Posts: 4,469
    Ironically

    It was Taco's FloPro University's lesson on circulator placement that caused my questions. In one segment the talk about the pressure being added back to the system on its way back down from the peak.Then they proceed to tell you it looses pressure on its way down from the peak. They use the example of 12 psi (all the system needed), and say the 12 psi was still present "Pumping To", but then have it dissappear with conflicting statements.

     I accept that it is the proper way, but can someone tell me where the 12 psi,or 4 psi that was left at the peak went. Obviously the pump affects the pressure, and is doing its part to maintain the 12psi (all the system needed)at its discharge.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Semantics at work...

    Chris, The OLD guys called it a "compression" tank. It basically recovered the system air coming out of suspension, storing it in the compression tank, which allows the air to be compressed and maintain the system pressure within a reasonable range. It will also compensate for fluid contraction. Regardless of its name, the final function is to maintain reasonable operating pressures by accepting fluid that is expanding from heating, and return fluid to the system when it cools down and contracts. Very similar to what goes on in your cars cooling system, but not quite.



    I've seen them referenced as compensation cylinders (UK), expansion tanks, contraction tanks, compression tanks and more.



    Kind of like someone else noted, you have to go to a manufacturers "pump" performance curve to find out what their "circulator" is capable of doing at a given point in its design/application. Although technically, a true "pump" is completely different than a "circulator", the term is used universally without issue.



    Head and pressure mean the same thing.



    There are a LOT of semantics in our industry, most of which are known and used by participants on a daily basis. I'm sure that others will chime in and give you more for your edification. Don't get hung up on the name. Just understand what the actual function is and its effect on other components within the system.



    And welcome to The Wall...



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Tom_133
    Tom_133 Member Posts: 883
    Just when you think you know...

    you read this thread in it's entirety, your brain hurts from the activity. Then you go outside grab a drill and poke a hole in your skull to relieve massive pressure from thinking, realize by doing such you've experienced pressure differential and question if that makes your heart a pump or a circ?



    J/K thanks for the info guys!! Lots to think about.
    Tom
    Montpelier Vt
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Pure...

    Nothingness ;-)



    Happy New Year Dan.



    Thanks to you and TLM for giving our industry a place to educate and communicate.



    Without it, we'd be lost...



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,513
    Mark, just so you know.

    And I KNOW you know. All that you've said here is true and the way this works. Thanks for taking the time to tell it again. I don't think we'll ever finish telling it but the alternative theories continue to amaze me. They're quite visual, very creative, but sadly, wrong.



    Thanks for caring enough to write like Tolstoy. ;-)
    Retired and loving it.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Too much static to hear you....

    Just kidding ;-)



    We're talking about two different pressures here. Static, which is the pressure required to raise the water to the very top of the system. That pressure is roughly 1/2 PSI per vertical foot of system elevation (.434 to be exact). Add 5 PSI to that to avoid flashing to steam if a negative pressure is generated, and also aiding in pushing air out of the top of the system.



    Dynamic pressure is the pressure that the pump/circulator/pressure differential machine adds to the system. Virtually EVERY ounce of pressure that the pump or whatever you want to call it generates, is "consumed" in moving the fluid around the loop.



    If it weren't, with every pass around the loop, you'd have a build up of residual pressure that will eventually cause the pressure relief valve to do its job, that being relieve excess pressure.



    Doesn't matter if the loop is one foot in length, or 1 mile in length. ALL generated dynamic pressure is COMPLETELY consumed in the piping network between the outlet flange of the pressure differential machine, and the inlet flange.



    Now, what the pipe does with that energy equates to flow. And it is also significantly affected by the pipe diameter. But lets not go there on this thread. Already confusing enough. Just know that dynamic pressure is added to static fill pressure, but only dynamic (generated) pressure is consumed in the process of moving water through the pipe.



    In a properly designed/installed/maintained system, the elevation pressure (a.k.a. feet of head) will always be the same, plus the added pressure from the pump.



    In an improperly designed/installed/maintained system it is possible to create a condition whereby the pressure within the pipe is less than the static pressure, but if this is the case, you have a WHOLE lot of other problems facing you. Hence the reason for my use of those qualifications. Under normal, good operating conditions, the static pressure should be relatively constant.



    Why maintenance? Have you ever seen what a Y strainer that has not been serviced will do to a system? I have, and it will make you scratch your head. Think HUGE pressure drop... and little to no flow.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Paul48
    Paul48 Member Posts: 4,469
    Thank You

    That answers my question. I am one of those people that has to understand something. My wife would say I'm a thick-headed Irishman, and that may be the case (to an extent). I appreciate your patience...Thanks.
  • Canucker
    Canucker Member Posts: 722
    This

    is why I come here. I have a lot to learn and I can't think of a better place to get the right answers for my questions.(Not the "because I've always done it this way" answers)

    I wouldn't call it thick headed to want to know why and how something is supposed to work. That's how you keep the snake oil sales to a minimum.
    You can have it good, fast or cheap. Pick two
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Tolstoy???

    Thanks Dan. Must admit, I had to look that one up...



    And to think that all I wanted was to have some Moves like Jagger, Moves like Jagger, Moves like Jagger ;-)



    The Leo Tolstoy of Hydronic Heating eh....



    Nah, doesn't fit my Western Wildman image ;-)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Jumper...

    The use of an open tank in the attic, like the old gravity systems, allows oxygen a direct path into the water. Not a good idea with the newer, thin panel radiators.... Now THERE is a concept that is hard to see in your minds eye. Oxygen going into and out of water freely...



    If, for some reason, bladder and diaphragmatic expansion tanks were to be outlawed, my tank of choice wold be the good ol' ceiling hung horizontal vessel connected to an air separator, connected to the tank with the B&G Airtrol fitting. The end result is NOT the same as having a microbubble air resorber that expels oxygen OUT of the system, but unless your system is running 24/7/365, when flow stops, the O2 content automatically balances out anyway. But, in a side by side comparison, the MBR will in fact take the O2 levels down many times faster than a conventional air scoop/auto vent separator. They both take the O2 levels to the same point, but the MBR does it faster, more efficiently.



    Speaking of outlawing expansion tanks, back when I was doing investigations of system failures associated with the Goodyear Tire and Rubber company hose (E2), the thin steel tanks so common on the market were rotting at the nipple connections and breaking off and flooding houses. In an effort to take care of this situation, the state boiler inspector decided to outlaw the installation of expansion tanks into the tapping that was MADE for mounting an expansion tank on the air scoop/separator... It was required that the tank be firmly mounted to the wall or floor, but not allowed to be installed in the taping that was designed for it...



    Basically, what they did was to eliminate the "CLUNK" associated with the tank rotting off and falling on the floor. The tanks continued to fail due to oxygen incursion through the walls of the tube, but at least there wasn't a large scary CLUNK associated with its failure.



    Government intervention at its finest ;-)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited January 2013
    Power Point presentation

    I did a presentation at the Mechanical Systems Week this last Fall.



    Here are three very descriptive slides showing the PONPC for the most common types of expansion tanks used, as well as an old Bell and Gossett picture that shows exactly what happens to the pressure (static and dynamic) with the pump in different positions.



    Hopefully, this will clear the PONPC up in everyones minds eye.



    Enjoy!



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • 28W
    28W Member Posts: 141
    Ah, shucks!

    As a non-pro, I had no idea how "pressurized" this topic was.  Thanks to everybody (and Mark in particular) for the patient, detailed explanations. 
  • bill_105
    bill_105 Member Posts: 429
    sizing

    I was asked last summer of the differences between a well pressure tank and an expansion tank. I answered "I don't think any other than the well tank has to deal with rusting" Is that right? And when is an expansion tank over sized?
  • icesailor
    icesailor Member Posts: 7,265
    Changes:

    I'm open to any change. I don't get to do many new systems anymore. Where I work, I see some of the most expensive systems that don't work properly, or ones that do..

    I'm just looking at my latest edition of P&M. There is an article by Siggy that is an example of what I am talking about. It theory and application it is perfect. In pricing and installation cost, it will be so high that it will not be installed and will be a gas warm air with heat and AC with one big cold air return on the first floor over the furnace or air handler. With a totally FU'ed AC system.

    Another Wethead job to the Airheads.

    It is said that Germans like technology for technology's sake. I'm German. I'm also Scots. That holds me back from going places that will make it so expensive that the installation becomes prohibitive. And I have to justify what I have done.

    My caution comes from the first time I met Dan H. at an Emerson Swan seminar for Taco and E-2. I've done a few E-2 installs but lucked out on them. The biggest problem I ever had with them was after explaining to everyone that had anything that had anything to do with the floor insulation and how it ABSOLUTELY HAD TO BE DONE. they did it wrong, and it never worked as advertised.

    Its really hard to screw up a good hydronic system. Simplicity was an old gravity system with great big pipes. But the flow was still the same as it is today. Just no restriction. Pumps allowed the pipes to be smaller. The pipes are now so small that it takes carefully selected pumps to keep the problems away. You're far smarter than I and have far more installation experiences that I do. But I know an over designed  and overly installed bad working system when I see one. Not everyone out there have the same basic understanding that you, I and others here have.

    Its the pumps. Its me in the field learning experience of pumps that drives me.

    Do you understand how ejector/jet pumps really work and what you can do with them over submersibles? And displacement piston pumps work?

    If anyone wants to know, I'll tell you . Otherwise, I don't want to bore anyone with my blathering.  It is related to hydronic pumps. Especially the part about how to get 5 GPM out of a 5 GPM well with a pump that can deliver 10 GPM.

    An old electrician, a crude one used to say, electricity doesn't care where it goes. A crude plumber I know says that water doesn't care where it goes. That may be true. I  like to see it go in good orderly direction, pleasing to me, my eye, and the eye of others. Pumps are the same way. But they do care where and how they get there.
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