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Ocation of expansion tank

Sweet_2
Sweet_2 Member Posts: 143
a post on another thread. I read 18" was the distance required between air seperator/expansion tank and circulator. How crucial is it to keep that distance. What would be the down side to butting the two up to each other. Presuming this is Pumping Away.

Comments

  • Alan_6
    Alan_6 Member Posts: 87


    It is the point of no pressure change. If the pump is too close to the water feeder, it will draw too much water into the system. It can also draw air into the system, from the air separator, if it is too close to the pump.
  • Big Ed
    Big Ed Member Posts: 1,117
    18\"

    You need 18" hozontal run before a typical air scoop. The run gives the bubbles a chance to rise near the top so the scoop can collect the gasses......
  • 18\" Not crucial but good practice.

    Depends really. I've read 10 pipe diameters from the PONPC. In my judgement this applies to air scoop type air removal systems. It's not really that crucially important but, you should observe this rule when using an air scoop. (if you have room). If you use a micro-bubble air resorber; (Spirovent) cut that distance down to nothing. I strongly recomend the use of micro bubble air resorbers as long as a diaphram type tank is used. These devices will suck the oxygen off of the planet if allowed to do so;-)

    I strongly disagree that an expansion tank needs to be mounted horizontally. There's more than one way to do things right. There is no right way to do things wrong.( G)

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  • 18\" Not crucial but good practice.

    It depends really. I've read 10 pipe diameters from the PONPC. In my judgement this applies to air scoop type air removal systems. It's not really that crucially important but, you should observe this rule when using an air scoop. (if you have room). If you use a micro-bubble air resorber; (Spirovent) cut that distance down to nothing. I strongly recomend the use of micro bubble air resorbers as long as a diaphram type tank is used. These devices will suck the oxygen off of the planet if allowed to do so;-)

    I strongly disagree that an expansion tank needs to be mounted downward. There's more than one way to do things right. There is no right way to do things wrong.( G)

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  • Sweet_2
    Sweet_2 Member Posts: 143
    Help me out

    On page 26 of Pumping Away there is an illustration of putting circ up against aire sep/ exp tk. Mentions "By creating differential pressure, the pump upsets the systems pressure equilibrium and creates flow everywhere-except, of course,in the line leading to the expansion tank" Just trying to understand the dynamics that would cause influx of air at PONPC. As you describe Thanks!!!
  • Darin Cook_3
    Darin Cook_3 Member Posts: 389
    Sweet

    You do not need to maintain 18" between the air separator and circulator. The 18" is for the " air scoop ". The manufacturer recommends 18" from the first 90'. It allows the air bubbles to rise to the top of the pipe ( laminar flow ) and go up the float vent. You most definetly can put the circulator immediately past the air scoop with the expansion tank and water feed piped into the bottom of it. This is pumping away from the point of no pressure change and piped in this manner will not allow circulator to trick pressure reducing valve into feeding water into the system. Hottest water and lowest pressure these are the ideal conditions for removing entrained air from a hydronic heating system. If you use a micrbubble air resorber you do not need to worry about any spacing requirements. Hope this helps.







    Darin
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    I guess we can agree...

    to disagree. I've never read a set of expansion tank instructions where they show it in any other position. I've not read every instruction booklet printed, but the popular models show it being installed in one position, with the nipple pointed UP on small tanks. Do you know something I don't? Care to share? It wouldn't be the first time I've been proven wrong, and it won't be the last...

    As for air scoops, if it is used on a primary loop where the velocity is ALWAYS at maximum, then it makes sense to have the requisite 18" INFRONT of the scoop. If you're dealing with a typical system where there are numerous zones, and the potential for max flow is acheived MAYBE 2 % of the time, it DOES NOT MATTER. How do I know? Because I have THOUSANDS of systems out there, and only ONE of them has the requesite 18" straight pipe consideration, and I've NEVER had any air issues. As Ken would say, "annectdotal eveidence..." maybe, but nonetheless, PROOF POSITIVE.

    Sweet, the PONPC is the hardest concept for my students to understand. Simply stated, it is the ONE place where the atmospheric pressure has an influence over the operating pressure of a closed loop heating system. The "atmosphere" is the air on the other side of the diaphragm on an expansion tank. In the case of a non diaphragm tank, it is the ONE point that air comes into contact with the working fluid. The pump can NOT influence the pressure at that point. And it WON'T influence the pressure at that point.

    Fluid does move through that point, but only due to thermal expansion and contraction, not due to any pumped pressures (assumes normal low head system circulators).

    In the case of a well pressurization tank, that's a whole different application. The submerged well pump CAN and DOES influence fluid flow at that point. It has to, otherwise every time you opened a tap for just a small draw, your well pump would turn on and off. The well pump MUST have the ability to generate enough pressure to cause the water to move into the diaphragm and store the energy (pressure) it produced in the tank. Different beast completely, and should not be confused with a closed loop space heating application.

    Now, with all that said, if you can hear substantial fluid movement within an expansion tank, it's an indication that there is a rather large compressible bubble of air residing out in the closed loop portion of the heating system. That bubble needs to be found and eliminated so that there is only ONE point of no pressure change.

    Here's some graphics to help you visualize the PONPC as it pertains to a closed loop heating system.

    ME
  • Sweet_2
    Sweet_2 Member Posts: 143
    ME thank you

    nice explanation , clarified PONPC. Quick question, why would the 18" , or how does it effect the PRV or differencial pressure that causesingress of air ??? AS always I appreciate yours and all of the expertise graciously given here.
  • Mark , got a question

    First , thanks alot for the detailed explanation of the point of no pressure change .

    Often we install the expansion tank at the end of the circulator branch . The circulators do pump away from the tank , but it's not really in the path of water flow . This is more a space conserving issue than anything else for us . Do you think placing the tank in this spot had any adverse effect on the PONPC ?

    Also , we see bladder tanks positioned every way possible , connected to many different points on a boiler . Regardless of the orientation , they all still have some pressure on the bladder when we remove them . A few weeks ago we took out a 15 Extrol sitting sideways with a date code of 1988 . Not water logged .

    Thanks again Mark for your time .
  • ME

    I won't pretend to know anything that you don't about hydronics and I'm not out to prove you wrong. You're never wrong;-)

    But, I have been installing expansion tanks nipple pointed DOWN on small tanks for a while and can't conceptually understand why they should not work exactly the same regardless of orientation as long as it is supported properly. I really like those 1/2" MPT x FPT Raven™ iso-valves w/bleeder vent. Sure helps when adjusting air pressure and might come in handy when the tank fills with water as they all will some day.

    I've replaced a few failed diaphram tanks as well. They were all in the orientation you reccomend.

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  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Sweet...

    You're welcome. You asked two different questions.

    Re: air ingress, air ingress is not a function the 18" of straight pipe before the scoop. The 18"'s has to do with laminar flow and allowing the air in suspension to collect near the top of the pipe before it enters the scoop. It has to do with air EGRESS. That said, if you have a situation whereby your pump is high head pump (think Grundfos 2699) and it is pumping towards the PONPC, AND the system is relatively tall, AND the residual pressure at the top of the system is relatively low (nearing zero PSI, AND there is an automatic air vent at the top of that riser, it is conceiveable that the circulator could create enough of a negative pressure to cause the automatic air vent to act like a VACUUM breaker, and dump all kinds of air into the system.

    These situations are realy rare, and ALL of the listed parameters would need to be in place before it could happens, but it can and does happen. If you are pumping away from the PONPC, the pump doesn't get the chance to present its' differential as a negative pressure, so air INgression is not an issue, unless you have a hidden venturi on your system...

    Remember this important fact. Pumps are nothing more than pressure differential machines. They DON'T care how their differential is presented to the system. They're just a dumb pressure differential machine...

    If they're pumping toward the PONPC, their differential is presented in the form of ALL subtractive differential. THAT'S where the problems begin.

    If they're pumping away from the PONPC, all of their pressure differential is presented in the form of POSITIVE pressure, and there are no problems associated with that, other than possibly lifing the relief valve on a boiler if the boiler is down stream of the pump AND the fill pressure is so high that the fill presure AND the pump differential pressure add up to more than the relief valve is design to handle. Again, rare, but possible consideration.

    Remember the comment about the pump creating all negative pressure? If the pressure reducing valve (PRV) is connected to the system in such a place that it can "see" the negative pressure generated by the pressure differential machine (pump, circulator, whatever), it kicks in and starts adding water to the system, because thats IT'S only function in life. Eventually, the whole shebang is overpresured, and the relief valve starts doing its job of releiving excess pressure, then your telephone starts riniging with a mad customer on the other end saying things like "It worked FINE until you guys started working on it..."

    One other point and I'll let is soak in for a while. The pumps location in relation to the expansion tank is important. The closer, the better. In the field, if the circulator is say 4 feet away from the PONPC connection, NOTHING should be installed in that section of pipe, especially water make up devices. That section of pipe will experience a pressure "droop". It's not enough to cause air to be sucked into the system, just enough to cause a lower operating pressure, which if seen by a PRV could result in over pressurization.

    Happy Hydronicing!

    ME
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Ron Jr...

    Based on what you've described to me, provided that your make up water connection and the PRV with that package is not between the PONPC and the circulator inlets, I don't think it's an issue. As I explained to Sweet, the piping between the PONPC and the circulator inlet experiences a pressure "droop". Not enough to go negative and suck in a bunch of air, just enough to fake out a PRV into allowing more water to flow into the system than is necessary. It will eventually hit a point of pressure stablization, but who knows where that point is and if its below the relief valves threshold.

    You could have the expansion tank located in another room if need be, it's just its' connection into the system that is important. I've seen some of the systems you work on, and they're enough to make a fella stand back, take a deep breath, shake his head and say "Huh!?!?", and I know you know this, hydronics is almost as much art as it is science.

    I've seen systems that were so theoreticaly screwed up that they shouldn't work at all, but they do, and they still produce heat. Heat is but one component of the comfort, and it takes a lot more than just "heat" to keep people comfortable. These "methods" that I'm promoting are considered relatively new to some of the old dogs in the industry. "My pappy did it that way for 30 years before I started doin' it, and I been doin' that way for 30 years and it works just fine! Ain't no way some snotty nosed punk from West of the Mississippi is gonna tell ME how to do my job..." So be it. I'm just promoting a scientificaly better way to do things. If your way works, keep doing it that way. My way works for me.

    Having seen your way of installing, you obviously do not fall under that category...

    Keep up the great work my friend. You're truly an inspiration to the industry.

    ME
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Gary....

    You've obviously never spent a great deal of time talking to my wife... I'm only human, and I do make mistakes, adn when I become aware of them, I admit them and try to correct my wrong doings. We're all only human.

    As for expansion tanks positioning, let me paint you a mental picture of why it's not a good idea...

    Also remember that in every drawing I've ever seen for a floor mounted model, the manufacturer recommends an air vent installed on the drop serving the expansion tank. Sometimes, they leave out all the juicy details as to why they're having us do something a certain way. They don't want to burden our minds with trivial information...AKA bore us with the details.

    ME
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Gary...

    With all due respect, you've obviously not spent much time talking to my wife about me...

    I, like you are only human. We all make mistakes. When I make mistake, I try and correct them as soon as possible to avoid collateral damage.

    As for the visual on the correct way to install an expansion tank, take a look at this and see if it helps your minds eye any.

    Have a hydronic kind of day!

    ME
  • Picture = 1,000 words

    Thanks for firing up the CAD.

    If a micro-bubble type air removal devise is used and properly located, I'm not sure any air would be trapped in the expansion tank after a day or 2.

    I understand that it's likely best to have the tanks as you prescribe for a more accurate fill pressure due to volume. I guess it does entertain me trying to prove you wrong:) Believe me, it would give me no greater pleasure (hydronically) to prove you wrong without having to ask your wife for any help;-) I won't rush out, go back & re-pipe the ones I've done, but I'll find a way to do it the better way next go around. The flames of wet head passion burn brightly here. Thanks for making this a hydronic kind of a day.


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  • Here's what two manufacturers had to say about orientation;

    From Watts website > "Note: Watts ET Series non-potable water expansion tank maybe installed in a tee or any other suitable tapping in the heating system and can be installed in a vertical or horizontal position."

    From Amtrol > "Inverted installation is of no consequence. Due to the fact that diaphragm tanks isolate air and water via a rubber membrane, they are not affected by mounting position. In fact, this is one of the main benefits of precharged tanks. Ease of installation and small size make them perfect choices for limited-access applications like you'll find in a residence."

    Ken Cerpovicz
    Amtrol Inc.

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  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    NO comment...

    I think I hear my wife calling me in the back ground...

    I'll have to get Robert Bean to post some pictures of horizontal expansion tanks, and vertical air seperators that he's collected over the years and see if they meet your approval:-)

    I'm going to continue installing them with their tappings in a vertical, up facing position.

    As I remember, it doesn't say anything in the installation instructions for air scoops about them having to be installed in a horizontal position either..

    ME
  • ex tanks

    Sorry to dredge this up again but,,, WRT expansion tank orientation, you last responded with "no comment." Every larger floor mounted expansion tank I've seen has had he air on top. Is this a conspiracy? I'll continue to do it your way as I believe you to be a true master. As such you are entitled to your opinions. It's a scientific mind that supersedes an OEM designs and prescribes it to his students. Thank you for your dedication to all things hydronicly correct.

    Gary

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  • Ken_8
    Ken_8 Member Posts: 1,640
    Gary,

    Mark is correct, but not for the reasons suggested, as you already pointed out. Any system with enough "entrained" air in it will be problematic after a day or two no matter where it resides.

    Quite obviously, expansion tanks are also made that are designed to be horizontally mounted. The bladder is no different than on those that have threaded connections on the end(s).

    The reason manufacturers suggest only straight up orientation is because side mounting would exert unacceptable torque on the thin sheet metal of the surrounding nipple/fitting and rupture easily should the EXP. tank become flooded or close to fully receptive!

    If you choose to hang the EXP tank to the side that is perfectly fine. You must however provide support to avoid all tension on the thread to vessel weld or you'll deform and rupture the tank at that already vulnerable mount..

    Think about it. Gary is absolutely correct. You can mount it in any orientation - as long as you support it properly.

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  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    No comment...

    was said with tongue firmly planted in the cheek. You obviously proved your point by dredging up manufacturers literature counter to my way of thought. To each his own.

    As for floor mounted tanks, the install literature I've seen clearly shows an auto vent at the top of the riser to expel any air that might get trapped at that point.

    Like Ken pointed out, the tanks are designed to be supported in a specific manner. If by the nipple, it SHOULD be hung vertically. If you want to go to the trouble of putting in Unistrut and using 10" clamps, then I guess you could (according to the manufacturers literature you found) hang it in any direction you want.

    FWI, The State of New Mexico, in all their unfinite wisdom, made it illegal to install expansion tanks hanging from the tapping on an air seperator. This was in response to expansion tanks becoming rotten and falling off. Instead of addressing the non oxygen barrier issue from a certain rubber hose that was causing the issue, they saw fit to ban that particular factory approved method of installation. The ends of the expansion tanks are still rotting off and leaking water all over the place, they just don't go CLUNK any more when they hit the ground...

    I respect your opine to do it as you please. I'm just interjecting my personal experience and common sense into the picture. Not everyone uses MBR's, and contrary to popular urbane myth, unless under CONTINUOUS circulation, MBR's do not suck oxygen off the next closest planet having oxygen in its atmosphere...:-)

    It's all cool :-)

    ME
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,235


    I just installed a Taco on a commercial job. It sat on the floor on its stand vertically and the system connection was at the bottom

    ED
  • Boiler Guy
    Boiler Guy Member Posts: 585
    Non diaphram tanks ?

    Mark your picture of the connection of a standard expansion tank shows connection to the top of the air purger. I agree with that, however since the top tapping is usually 1/8"; how critical is the orientation and pipe size connecting this expansion tank? What, in your opinion would be the min/max pipe size?
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    BG...

    That was for visual demostration purposes only. I don't actually recommend the use of non cap tanks. I like to get the air out and keep it out to minimize oxidation potential.

    That said, I have seen air scoops with larger air taps for recovering the air and sending it back to the cushion.

    I have also seen cases where the air seperator (scoop) was turned upside down to facilitate a non cap tank. It worked fine. The scoop is really nothing more than a fat spot in the line to slow the flow and allow the air to rise and accumulate. I've seen some early versions of air scoops that were literally nothing more than just that, an increaser, a short (1 foot) run of pipe, a decreaser and the rest of the system. They worked (are still working) quite well. The baffles that are put into these new cast iron scoops are someones idea of how to enhance air seperation/elimination, and they may very well add to the efficiency of the seperator, but as has been proven, it CAN work without them (baffles).

    As for pipe size, the minimum and maximum would be dictated by the tapping on the tank. If its 1/2", then that would be my minimum recommended connector size.

    Did I answer your question?

    ME
  • Boiler Guy
    Boiler Guy Member Posts: 585
    Yes

    It was just a point of curiosity for me. Had a lil tete a te with a "professional" who used 1/4" plastic pneumatic tubing as the expansion tank line. (Hey its rated at 125# @ 90F and the tapping is only 1/8). Could NOT convince him he was courting disaster. Four inches of water in a finished basement after a romantic weekend away .............. Gawd, I HATE it when I'm wrong!
  • hr
    hr Member Posts: 6,106
    Iffin you

    foolishly connect a "uncoated" steel expansion tank to, lets say, a non barriered tube radiant system, better plan on that expension tank connection failing! It's generally the thinnest ferrous component in most hydronic systems.

    Acidic glycol will take them out quickly, also!

    It's not a matter of if, but when :)

    Regardless of the mounting position, I feel ALL tanks should be supported by means other than the nipple connection!

    I'd like to see manufactures of tanks, or maybe the aftermarket "bracket" folks, offer a thin gauge "unistrut" clamp to fit around expansion tanks. Plenty of unistrut available :)

    Surely, Shirley an adjustable (one size fits all" one could be easily fabed. Or a real large, wide stainless hose clamp!

    I remote mount a lot of my exp tanks. I use PAP for this. A quick and easy "stool" can be made from a scrap piece of 4 or 6" pvc to set them on the floor along side the boiler.

    This way they don't have far to fall :)

    hot rod

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This discussion has been closed.