Pressure problem

KCA_2

Hi guys..



  I have a brain twizzler...  I didn't pipe it but I have a problem that I need to solve..



A modcon boiler with at best a 4' primary loop...  A 0014 Taco on the return side pumping into the boiler...  Just before the 0014 there is a set of close tees (1 1/4 x 1") to the secondary...  No expansion tank on the primary loop..  Just the circulator...

The expansion tank is set at +- 17psi...  It's on the supply side of the secondary just after a spirovent and water makeup...  About a 15 gallon system and a #30 expansion tank...



The system won't run at 17psi...  it wants to run at 22 psi...  Gauges are on the primary before and after the 0014... Every once in a while the pressure creeps up to 30 and the pressure relief blows off.....  It's not temperature related as the temp can be going own (180degF & dropping) when this happens...  I've thrown a #60 expansion tank on just to see if that would help but...  Nada...



Why does the system want to run at 22 when the expansion tank is at 17psi?

What about the creeping up to 30psi? 



any thoughts?  I've even turned the make up off to see if that would matter...



Anyway....  Thanks in advance...



 KCA

icesailor

Pumps & Preessures:

Is it piped as per the boiler manufacturers suggested drawings?

A 014 pump has the potential of pumping over 30 GPM. Does the primary loop need a pump as big as this? What is the system pump?

Without a photo, it sounds like an unusual piping job.

Steve Whitbeck

pressure

The expansion tank pressure does not control system pressure unless You have a filltrol tank system, The pressure in the expansion tank is set too high - it should be 12 PSI. It sounds to me that your pressure reducing valve (PRV) is leaking water into the system. turn the water off to the system and WATCH the system pressure to see if it stays put. If it does replace the PRV.

KCA_2

The Manufacturer

requires this 0014...  as a matter of fact..  it comes with one...  There are 6+- zones all pumped..  all zones share a return...  The zones are a grundfos 1558...



I shut off the pressure reg and same thing happens...

KCA_2

Filltrol

Hi Steve...



  I pretty much fill the expansion tank to the pressure that I want to run the system at...  Maybe you could explain your point of view.. 



  Thanks

Paul48

Bass Ackwards

It is not necessarily the source of your problem, but the boiler loop should be off the closely spaced tees, so it's circulation is unaffected by system circulation.Is your temp at the boiler spiking?If you stall the circulation in that boiler,it would probably boil before it has a chance to shut off.

KCA_2

Once again?

The boiler loop should be off the tees?  Restate that if you don't mind..  Lol...

Paul48

Bass Ackwards

The boiler loop should be off the closely spaced tees, so it is unaffected by system circulation.

Paul48

For

some reason replies are way down at the bottom of the page?

PeterNH

blank lines

Some sort of glictch happened in Steve's post.

Maybe he can edit it and remove all the blank lines.





Peter

KCA_2

??

don't know what you mean by "off the tees"

Paul48

In

other words.....the end of the boiler loop should be the closely spaced tees.

lchmb

your

expansion tank should be filled to the starting pressure of the system. Another words what your pressure reducing valve is set to. In most case's that is 12lbs. Once filled and purged, your system will then run to approximately 20lbs when heated to 180 degree's. Buderus GB142 does want the system set to 13lbs when filled and you would set the expansion tank to that. It has to do with a pressure switch in the boiler and what they want to the system to see for pressure....

KCA_2

Set the expansion

tank at 12....  and let it run at 20?  I don't get it..  the tanks diaphram would be over extended all the time...  Is that correct?  Maybe I don't understand the idea here...

icesailor

Pressure Pumping:

Well, you have an interesting situation.

Some may say that I am full of $chitt. But, with that 014 pump, pumping in the primary loop, and the closely spaced tees, probably not properly installed, the first pump and its pressure can act as a first stage in a two stage pump. The second pump, on the secondary side, if it sees a lot of pressure bleed off fthrough the (improperly) spaced tees, the rise in pressure will be collected by the second system/zone pump and be multiplied. Why it doesn't drop back when you shut the system down is a quandary. But there has to be some problem in the hydraulic piping. A low loss header or hydraulic separator is a better choice than closely spaced tees if they are not properly installed.

It would be interesting to see if you had four pressure gauges. Two on either side of the closely spaced tees on the primary loop and two at the secondary where it enters the closely spaced tees coming too and from the system loop, with all circulators running.

You didn't do the install. Look at the system and think of how you would have piped it. What's different?



Taco says this about installing closely spaced tees. Read down about design and the drawings.

http://www.taco-hvac.com/uploads/FileLibrary/102-145.pdf

I see a lot of installs where part of the "closely spaced tee" is a tee with the primary and secondary run going through the Run of the tee and the branch or bull goes to the other tee. That's not how it is shown in any drawing I have ever seen.

icesailor

Boiler loop:

You do mean that the boiler loop must run through the run of the closely spaced tees and the secondary or system loop goes through the branches of the tees?

Like in these drawings from Taco?



http://www.taco-hvac.com/uploads/FileLibrary/102-145.pdf

Slimpickins

isolate indirect coil

There may be a small pinhole leak on your indirect tank coil and the house pressure entering your boiler side pressure. Isolate the tank and see if pressure doesn't rise and you've found your problem.

icesailor

Rising Pressures:

That would be the way to go if the pressure built when the system was at rest.

It was my understanding that the problem occurs when the system starts to heat and the pressure then rises..If it is a coil leak, the pressure would rise all the time and the relief valve would be constantly leaking.

Is this a Combi unit?

Paul48

Actually

those Taco drawings show boiler primary, and most if not all mod/con manufacturers want boiler secondary.

Steve Whitbeck

Sorry

didn't realize that my dog had her paw on the computer and had added a LOT of blank space.

The reason for having the same pressure in the tank as you want your COLD system pressure to be is that when the system is cold there isn't any water in the tank. The air against the diaphram keeps the water out. As the boiler heats up the expanded water pushes against the diaphram and pushes water into the tank. If you have too high of an initial pressure in the tank - say 17 PSI - Now the system has to get to 17 PSI before the tank can absorb any water. 30 minus 17 PSI gives you less room for expansion than 30 minus 12 PSI.  If the air pressure is less than the cold system pressure then the tank already has water in it before the system even starts to heat up.

icesailor

Primary/Secondary:

I must have missed something in learning. Every modern boiler I have seen lately shows the boilers being piped directly so that there was absolutely no possibility of restricted flow through the boiler with the boiler being the primary loop. All else comes off of that becomes the secondary loop. No matter how low the flow in the secondary loop, the boiler flow is always high, cooling the boiler.

HTP Munchkins use the Indirect as part of the primary loop.

Veissmanns suggest you use a low loss header or hydraulic separator. Boiler on one side, system on the other side.

It is my understanding that the reason behind P/S piping is to control unequal circulation pressures in two sets of circuits that are connected.

Perhaps the boiler/system in question is piped in some unusual way?

My point is showing that drawing from Taco is how the closely spaced tees are drawn. 4 to 6 pipe diameters between tees does not mean that is the boiler loop is 1" pipe, you do not use a 6" nipple between 2 one inch tees. Because you probably have 8" C to C between the tees. A 4" nipple will barely make it. It is my understanding, that the closer the tees, the better the circulation through the runs of the tees. That high flow is what keeps the boiler from turning into a steam bomb.

That distance from an elbow, from the horizontal to the vertical to the closely spaced tee is very important Sometimes you can violate the rule. When you can't, you will never figure out that that is the problem.

Unless the problem in question has a leaking indirect coil, it may have a piping problem. Especially if you use those rotten IFC pumps. You could have a problem like we used to get with zone valves and the pressure tank installed between the flow check and the zone valves.

  

KCA_2

That was the problem

a few weeks ago..  The owner had the original contractor put a new tank in and a few days later it's happening again...  I can't imagine that the tank is bad again....  but I guess stranger things have happened...



  :-)  Thanks

KCA_2

The unit

is a Ultra 230 Weil McLain

Paul48

Maybe

I'm reading something wrong..... http://www.t4engr.com/understanding_primarysecondary.htm

Mark Eatherton

High head pumps, PONPC, and Pressure reducing valves

Kenny,



I've tried reading through all of your answers, and comments, but the ONE time (other than the obvious DHW that is cross connected) that I have seen this creeping pressure phenomena is when a high head pump has the make up connection anywhere near its inlet, and this pump is pumping towards the PONPC. When the pump first starts, before everything (fluid) gets rolling along to the point of equalibrium, the pump CAN and WILL create a significant droop in pressure that the reducing valve "see". It immediately spits a little water into the system. Each time the pump starts, the PRV squirts a little more water into the system, and eventually the pressure reaches the relief valve threshold, and GOOOSSSsshh, all that excess water is relieved, and replaced with oxygen and mineral laden water, and the cycle starts all over again.



Turning off the make up water SHOULD have exposed this as a potential. The water pressure SHOULD have remained stable, if in fact this is the problem. If the pressure still rose, then it indicates a cross connection of the coil of the DHW system, over pressuring the space heating side of the system.



If my assessment is correct, AND the pressure drop down stream of the pump is increased, then the problem is exasperated over time. Initially, it stops due to hitting a point of equalibrium, but if the circuit the pump is serving gets clogged, the problem becomes even more pronounced, and we all know that lime scale accumulation in a boilers water way is guaranteed cause additional pressure drop.



Look at the system with a critical eye and make certain that all pumps are pumping away from the PONPC, and that none of he pumps has the makeup in such a position that it could "see" the negative pressure being caused by a pump pumping towards the PONPC.



Hope this helps.



ME

KCA_2

Why?

do you say that?

KCA_2

It turned out that...

The Weil McLain side arm was passing pressure...  Again...  It's the second indirect on this project in a month...  I didn't install them I was just asked to locate the pressure problem...  I can't believe that there were two.....



Mark...  did you read the other comments here about the expansion tanks?  set at 12psi and let run at 20psi..  and the like...  It doesn't seem like there is much common understanding about expansion tanks...  I'm surprised..



  Anyway...



  Have a great day!!



 :-)  KCA

Mark Eatherton

Hmmmmm...

One failed tank, a fluke.



Two failed tanks? Alarming.



If this is their (actually Triangle Tubes) tank within a tank design, the inner tank MUST be filled AND pressurized prior to filling the boiler side of the system, or it WILL crush the stainless steel tank like an aluminum beer can...



I'm betting the manufacturers rep is going to want to take a real close look at the second tank.



Regarding the expansion tank, it is normal for a system to experience more pressure hot than it does cold. You could keep the pressure extremely low in fluctuation, but you'd have to have a BIG expansion tank, and its not worth the extra money to do so.



The biggest common problem that I have had with the newer type of captive bladder diaphragm tank is the diaphragm getting stuck to the tank and not accepting any fluid expansion.



For that reason, I find myself figuring out what the minimum operating pressure is that is required to raise the water to the highest part of the system (plus 5 PSI), air the tank to that point, then fill the system to around 6 to 8 PSI above that so that the diaphragm is held away from the face of the tank.



HTH



ME

KCA_2

I talked to Brandt

This morning about this...  He said that they are getting away from the tank in tank design from Triangle Tube..  I like them....  I don't like these failures though...  He seems good to work with ...



Do you know that Taco requires 20psi on all  circulators over 5000 ft ASL?  I've been asking why but can't get an answer... Something to do with flashing in the cartridge...  So...  you wouldn't run the system at 20 and the ex tank at 12psi....  would you?  You'd pump the expansion tank to 20psi...  right?



:-)

Mark Eatherton

Right....

If you left it (diaphragm) at 12 and ran it (system) at 20, it would take up some of your tanks acceptance capacity. In most cases, the expansion tanks are oversized, so its no big deal, but in situations where the tanks size is marginal, it could cause issues.



Another thing that cracks me up is people who worry about the excess stress caused by running their systems at 25 PSI. The components are all rated and tested for pressures well in excess of the 30 pound relief valves capacity. Don't worry, be happy :-) Higher pressure means smaller bubbles means less air bouncing around the system. As long as a person stays at least 10% below the relief valves threshold, they will be fine.



It is NORMAL to see an increase in base pressure when the boiler is running hot. Not sure where or how the rumor got started that the pressure is always supposed to be the same regardless of operating temperatures, but its just not true.



The sizing of expansion tanks takes numerous variables into consideration. One of those is the highest water temperature, which the system will see. It is virtually IMPOSSIBLE that the system would EVER be completely filled with "XXX" temperature water, because heat is continually seeking equalibrium with the fluids (air) surrounding the pipes. Plus convectors are SUPPOSED to shed heat to the cooler fluid (air), so this causes most expansion tanks to have a considerable buffer in their sizing.



Relax, don't worry :-)



ME