Flushing 2nd floor hydronic system loop to purge air

MarkZeh

Need some help resolving an issue flushing/purging air from 2nd floor hydronic loop. I follow the same standard procedure for flushing first floor zone, which functions perfectly. However, there's an issue flushing on 2nd floor zone. Every time I bring Taco water valve to full flow/street pressure it pops the 30psi safety relief valve at around 25psi. I've been able to do a slow purge with water not exceeding, maybe 20 psi, but any higher the relief valve pops. Anyone ever seen this? could a faulty, partial closed gate purge exit valve cause a flow restriction and pressure spike? Maybe replace exit gate valve anyway? As Relief valve if popping around 25psi just not getting the opportunity and sufficient time to flush/purge air out properly. Maybe install in-line auto air bleed valves on 2nd floor. So frustrated. Any thoughts/suggestions?? many thanks

delcrossv

Is that off the boiler gauge? Actual pressure would be your city pressure plus the head height to the 2nd floor.

MarkZeh

Delcrossy, thanks. The pressure that the relief valve pops is the pressure I'm reading on the boiler as I move the Taco diaphragm lever towards 'Full open'. Once she reads ~25psi it's only a matter of seconds before the relief valve pops. This DOES NOT occur when I purge/flush the main floor. Either it's a height issue, trying to get my arms around that concept or why? or could there be a restriction somewhere that would make the 2nd floor loop spike in pressure. Wonder is the gate drain valve might be failing staying partially closed. Frustrating n=my friend.

delcrossv

Relief valve pops at 25#? Should be 30. How old is it? (they don't last forever)

You may try partially opening the fast fill and watching the gauge. If your 2nd floor loop is 20 feet above your boiler you're adding 8.66 psi to the city water pressure- even if your drains are open.

MarkZeh

Delcrossv, OK, checked, new 30psi pressure relief valve installed Dec 2022. Could always be defective but nominal operating system pressure has been about 20psi w/o issues. It's only when I go to purge 2nd floor to remove air under full city flow/pressure that relief valve pops. 1st does not exhibit the same problem. Have since tooled down the pressure post Taco valve to 15psi. That should me more than enough to cover 2nd floor fill (20ft max). I'm gonna check for anything odd in loop as well as shut down boiler and examine the drain gate valve installed. It just might be opening all the way causing the city pressure to spike up. Also wondering if the relief valve is now compromised from popping a few times and no longer holds at 30psi but is now down to 25psi. Let me know if you have any thoughts and/or suggestions. Appreciate all the help. Thanks!!

MarkZeh

sorry - drain gate valve. 'might NOT BE opening all the way'

EdTheHeaterMan

@delcrossv said "If your 2nd floor loop is 20 feet above your boiler you're adding 8.66 psi to the city water pressure- even if your drains are open."

I don't understand that comment.

If I am putting 45 PSI city water pressure into the boiler and the boiler has a radiator 20 feet above the boiler feed inlet, the water pressure will be 53.66 PSI? Please explain this to me.

OR If I am putting 55 PSI city water pressure into the boiler and the boiler has a radiator 20 feet above the boiler feed inlet, the water pressure will be 63.66 PSI?

OR If I am putting 75 PSI city water pressure into the boiler and the boiler has a radiator 20 feet above the boiler feed inlet, the water pressure will be 83.66 PSI?

EdTheHeaterMan

@MarkZeh as far as putting pressure in your boiler to get the second floor air to entrain with the flow of water DOWN to the boiler room purge station (valve) is concerned: If your relief valve is opening before you get enough pressure to purge, then your purge station is set up wrong and you may need to have a professional redesign it, unless you feel comfortable with that as a DIY project. I would wait until the weather is nicer to take on that project.

Can you post a picture of the near boiler piping from the floor to the ceiling so we can all look at what your are describing. There may be a better way to purge without the relief valve discharging.

SuperTech

The boiler fill valve is a pressure reducing valve. The pressure going into it doesn't really matter. 

delcrossv

@EdTheHeaterMan Head height, Which is why you don't see hydronics in skyscrapers.

EdTheHeaterMan

delcrossv said:

@EdTheHeaterMan Head height, Which is why you don't see hydronics in skyscrapers.

????
This is your answer to my query about your comment about adding Head of a 20 feet to Pressure?

I still don't understand.

Did you mean that if a building is 2 stories above the basement with a boiler in the basement so the top radiator is 20 feet above the pressure gauge, there will be 8.66 PSI which is equal to 20 feet of head on the gauge.
AND
That same building has 57 PSI of city water pressure on a pressure gauge at the water meter in the basement water service feed.
WHEN
You open the boiler feed valve to the city water pressure in that building the gauge will change from 57 PSI to 65.66 PSI?

Because that is what it sounds like you said here:

Relief valve pops at 25#? Should be 30. How old is it? (they don't last forever)

You may try partially opening the fast fill and watching the gauge. If your 2nd floor loop is 20 feet above your boiler you're adding 8.66 psi to the city water pressure- even if your drains are open.

And I can't agree with you.

What I can state is that if you open that boiler feed valve to the 57 PSI city water pressure, The boiler pressure will increase to 57 PSI (or 132.8 Feet) if the relief valve does not open because it is defective or non existent, or increase to 30 PSI or (69.999 Feet) and open the relief valve.

I can guarantee you that the 20 feet of water pressure from the boiler will not in any way affect the city water pressure of 57 PSI or any other water pressure the city may provide above 10 PSI to that home.

Correct me if I am wrong. I want to learn everything I can about this science called Hydronics.

delcrossv

Did he say his city pressure was 57 psi? I don't recall that. I do recall 27 psi. All I am saying is that if he purged the lower loop at 27 and closed it, then filled the upper loop and left the water on, he would see the sum of the head height and the city pressure which would add to over 30. I don't think we're in disagreement except for city pressure. Once the input from the city is closed, what's the source of the pressure squeezing the air in the compression tank? It's not like water is compressible.

If I'm off on this I'm happy to be corrected, but it's not that the water in the 2nd floor loop weighs nothing (?) I'm all about learning something too.

EdTheHeaterMan

delcrossv said:

@EdTheHeaterMan Head height, Which is why you don't see hydronics in skyscrapers.

????
This is your answer to my query about your comment about adding Head of a 20 feet to Pressure?

I still don't understand.

Let me rephrase my query

Did you mean that if a building is 2 stories above the basement with a boiler in the basement so the top radiator is 20 feet above the pressure gauge. there will be 8.66 PSI which is equal to 20 feet of head on the gauge.
AND
that same building has 27 PSI of city water pressure on a pressure gauge at the water meter in the basement water service feed. (Which seams low for city water pressure but I will work with you on this one)
WHEN
You open the boiler feed valve to the city water pressure in that building the gauge will change from 27 PSI to 35.66 PSI?

Because that is what it sounds like you said here:

Relief valve pops at 25#? Should be 30. How old is it? (they don't last forever)

You may try partially opening the fast fill and watching the gauge. If your 2nd floor loop is 20 feet above your boiler you're adding 8.66 psi to the city water pressure- even if your drains are open.

And I can't agree with you.

What I can state is that if you open that boiler feed valve to the 27PSI city water pressure, The boiler pressure will increase to 27PSI (or 62.9 Feet) if the relief valve does not open because it is defective or non existent, or increase to 30PSI or (69.999 Feet) and open the relief valve.

I can guarantee you that the 20 feet of water pressure from the boiler will not in any way affect the city water pressure of 27 PSI or any other water pressure the city may provide above 10 PSI to that home.

Correct me if I am wrong. I want to learn everything I can about this science called Hydronics.

delcrossv

@EdTheHeaterMan Did you read my last comment? If you'd like to comment on that, I'm listening.

EdTheHeaterMan

Your last comment says that you did not know if he actually has 57 PSI city water pressure.

I still don't see how boiler 8.66 PSI will add to any water pressure over 10 PSI from the city water service. I believe because I selected 57 PSI as a city water pressure you invalidated my query. So I used your 27 PSI as the city water pressure to revalidate my query.

You have not explained the part about " you're adding 8.66 psi to the city water pressure" that you stated. I am looking for the logic to the statement you're adding 8.66 psi to the city water pressure. Please focus on just answering that query. Please disregard the actual city water pressure an focus on how 8.66 psi gets added to the city water pressure, what ever that pressure might be.

I hope I have made my question more clear.

I apollogize for any misunderstanding in the way I worded my query previously.

delcrossv

OK. No worries. How much pressure does a column of water 20' high provide? If you disconnect the city line, you still have the water column. Where does that weight show up? The gauge, yes? Even if you had and old time open system with the open tank in the attic, a gauge on the boiler would read pressure from the column of water, right?

EdTheHeaterMan

Since the OP is not in the trade, and for others who may read this in the future, I do not want them to think that we are just able to add pressures from one place to another place and come up with a higher pressure than what actually exists.

If the city water pressure is only 27 PSI then no matter how much water you can force into a 20 FT high boiler system, You will never get more than the 27 PSI of that water system

Likewise if you have 47 PSI city water pressure and you have 8.66 PSI water pressure in the boiler, you can not add those two pressures together to get a higher pressure then 47 PSI.

But to get back to solving the problem for @MarkZeh. If they can post some photographs of the near boiler piping and the purge station there may be something that they can do to get the air out. Without the photos, there is no way to help. The photos should be far enough back to see the boiler with the pipes from the floor to the ceiling and from at least 2 different points of view. high and low or left and right. Or maybe all four points of view.

MarkZeh

Gentlemen, can't thank you all enough for the insights and push, even academically, to resolve this. OK, my take. Agree with Delcrossv, height of 2nd floor, 20ft close enough, yields 8.65 psi as a couple pressure. But agree that once you swing the Taco valve handle to 'fast fill' you're by passing the regulated function of the valve and introduce full city flow and pressure. Have no gauge on incoming city water source but Suffolk County NY advises roughly 45-50 psi. So, once city pressure is introduced the new pressure introduced to the 2nd floor, or 1st floor, loop is the 50psi. OK, with all that said, so by introducing the 50psi to the system, why does the 2nd floor loop pop the relief valve and the 1st floor does not? Something ain't right here. Since city pressure is NOT introduced to the loop until the exit drain valve is already open, there should be no build up of pressure in the loop to the 50psi level unless the drain valve/or a restriction exist in the loop. Relief valve is functioning properly activating close to 30 psi. Might be weakened by now from repeated popping. OK, my plan of attack here. Gonna take and send pics of near boiler piping for all to see. BTW, my boiler has the same configuration of the one posted by 'Fix it with Zim' air purging tutorial on Youtube. Next, goona re-purge 1st floor loop and not the reading on the boiler pressure gauge so we better understand what pressure is being applied to the boiler once full city pressure has been introduced. Then will close up 1st floor zone and move to 2nd floor zone. Will remove and inspect exit gate drain valve for defects as a defective partially opening gate valve may just be the root cause of all this annoyance. Is it too early to hit the Bourbon yet??? Keep you amigos posted on finding. 1MM Thanks

archibald tuttle

first, to practically solving your problem, and second to the theoretical debate about whether the standing column of water in your heating system would result in an additive pressure reading to city water pressure.

@EdTheHeaterMan is 100% correct, if you are bleeding the loops and your blowoff is going, you either have not engaged isolation valves or your system is not well set up for bleeding.

I always provide for isolation of the boiler from the loops during bleeding. this isn't really a question of whether your blowoff is properly calibrated as how do you know that your pressure gauge is better calibrated than your blowoff. I always want more than 30 lbs to bleed multi story and I never use the override on the pressure reducing valve, i tee after the backflow preventer to a ballvalve for bleeding. usually i am able to use the same entry point to the system as the make up water but occasionally the location of the "point of no pressure change", i.e. the pressure regulated make up water and expansion tank is incoveniently located for bleeding so that ball valve leads to a different tee. generally that input should be able to be isolated from the boiler both by feed and return shutoffs and able to provide flow commensurate with any check valves to each loop. on the opposite end of the loops i use tees to pex to an air gapped trap (typically for instance a nearby washing machine drain, for bleeding although many would have a hose thread and use a hose to such a drain or out a window.

so the point is to isolate the boiler and its blow off located either on the boiler or near boiler piping so then we don't have to debate the theory of whether the height of the water column is showing pressure gauges and reliefs a higher pressure.

but on that interesting question, i think of it the other way round. the head is subtractive from the incoming pressure at its peak. that is why you need the additional pressure to bleed the peak. because putting in 25 lbs really only gives you a lazy 15 lbs or so to bleed with. i much prefer domestic water pressures for bleeding so you are getting more like 40 lbs of force over the top of the system.

but this scenario explains why, in my mind, this does not create additive pressure. because (not circulating, at stead state, the pressure in the system at higher elevations in the building is lower! so you add the lower pressure to the head pressure and you come up with the prv pressure or the bleeding pressure if it is overridden.

now when this gets interesting is when the system is circulating. so you have additive pressure from the circulator on the feed but then you have head loss related to altitude and pipe friction. on a tall building with 4 stories of heat in fan coil units I have, I originally ran heatmaker hotwater makers which are capable of 150 psi operation and that took care of my bleeding problems ( I actually ran the system at 40 psi with a 50 lbs blow off. but eventually i transitioned to munchkins which I'm very happy with but had to lower the system pressure. I still have 30 psi on the feed (which would either cause blowoff or dripping at the reliefs) but its coming back to the boilers at 24 psi so no blowoff but still a happy amount of pressure so i seldom air up one of the fan coils.

I'll sit back and watch now.

brian

(PS don't think I saw a picture of the near boiler piping to know whether you might have bleeding isolation. before I really got into orienting my near boiler piping for built in bleeding solutions i used to just throw a hose outlet on each leg of each loop after loop isolation and I would use a double female off the washing machine cold as the input for bleeding, yes that neglects backflow but i was running full city water in to loop and never left it on for odd conditions to ensue, although now i have all systems with a backflow protected tee for full pressure bleeding.)

EdTheHeaterMan

Still waiting on photo of near boiler piping, however without that actual piping diagram I will refer to this "recommended" purge station diagram that I used in my one day seminar I used to teach for www.EH-CC.org on Hydronics. Since I can not show the animation of this slide, I will describe what is happening here by adding some letter.
The illustration starts out with no red arrows or red lines on the valves.
1. I describe this as a new system with no water at all in it. all the pipes, and the boiler are filled with air.
2. I add the red lines that indicate all 4 valves are closed. One full port ball or gate valve on the supply and Three on the return.
3. Then I add the water pressure arrow marked by the letter A
4. Since the valve marked B is closed, no water pressure can go into the boiler in that direction
5. All the city water pressure is forced to go in the other direction indicated by the letter C
6. Once the city water pressure is charged into the system all the zones are charged with Umpty-seven PSI city water pressure. That same pressure is compressing the air in the radiators to the same Umpty-seven PSI city water pressure all the way to the three valves on the return just before the boiler indicated by the same letter C.
7. Since those three valves are closed the city water pressure is not going to effect the boiler relief valve.
8. With the hose connected to the open, purge/boiler-drain valve at the top of the supply pipe the next step...
9. Then the return valve on the first floor zone D is opened (one small red line on that valve above the letter D goes away in the animation)
10. Then the blue arrows E start to move indicating the city water pressure is forcing the air out of the pipes and into the boiler. The the boiler fills with water as all the air is discharged out the hose connected to the purge valve.
11. The animation continues to show zone 1 closing and zone 2 opening and the air is forced out in the same manner, then the zone 2 valve closes and the zone 3 valve opens and the air from zone 3 is purged using the maximum amount of water pressure to move the air from the top floor, down the return, into the boiler and out the same purge valve.

This is the best practice for setting up a purge station, and has served me well for many years. I learned that "single boiler drain purge station" idea from a very smart and humble individual who wants to remain nameless, but his initials are @DanHolohan.

EdTheHeaterMan

I can only guess that this might be the way the purge stations are set up. this will allow the city water pressure to be in contact with the boiler relief valve and limit the amount of high pressure you can use to force air from the top floor.



Still waiting for @delcrossv to confirm the water pressure addition theory. Or do you use the square route of the Umpty-seven PSI with the cosign of the hypotenuse of the right triangle measured between the city water tower and the boiler gauge in relation to the 20 foot percentage of 8.66 PSI with regards to the Straw-man receiving his diploma from the Wizard. and calculating the additional pressure in order to purge the second floor.

MarkZeh

Sir Edtheheaterman, your 2nd drawing is nearly spot on. Drain valves per zone. Only additions to drawing (before I send pics - by tomorrow am) are the 3 ball valves, 1 for each zone just above the recirc pumps but ~6" below the drain valves. Incoming city water supply: Water supply feed directly into Taco regulator then into boiler feed pipe. Below the recirc pumps feeding directly into boiler (slightly to right of yellow boiler box in dwg). True to your point, the pressure relief valve then sees the full city upon moving Taco lever to full flow. If the loop pressure exceeds the 30psi, sure the relief valve will pop as it's designed to.

Note: agree with the fluid dynamics statement from Mr. Tuttle
'i think of it the other way round. the head is subtractive from the incoming pressure at its peak. that is why you need the additional pressure to bleed the peak'
Spot on as this has something to do with a well known friend....gravity

Meanwhile, pasted the link to the youtube tutorial from Zim ( https://www.youtube.com/watch?v=voS7Url50M4) on how to purge air from zone designed boiler set-ups. Mine is set up the exact same way. Will get those pics and provide other data points as requested/promised , but still driving me batty as to why the pressure relief valve pops on 2nd floor purge and not 1st floor. Understand all the jargon regarding the need for some extra pressure to purge air from a loop 20ft higher than the boiler compared to 1st floor, but popping the relief valve religiously.
Can't say how much more I'm learning from the experts chiming in here. Talk soon and thanks!

archibald tuttle

@EdTheHeaterMan my only departure from your educational diagram is I like a purge station and additional main valve on the common return between D and E. this allows full city pressure purging without every hitting the boiler. not just the ability to really get up to boiler pressure less head in the loop.

then, i tend to short purge the boiler (unless there is a swing check at the elbow shown) to that station between D&E station and because that is low check retained air at the blow off or once largely purge reverse for long purge to the station you show.

now with all these letters, I know the ones you least want to go up against are DH but thats my take. and of course my purge stations whether on the common return or on each loop return are ball valves to pex to a an open drain connection.

MarkZeh

Dear all, kindly see attached pics of boiler and near boiler piping. BLR originally piped with 5 zones but where only 3 were used. Recirc valves and zones are zones 1 thru 3 moving from left to right. Water supply comes via a 1/2" copper line with a small yellow handled service ball valve. Water line extends downwards piped directly into the Taco regulator valve feeding the boiler. Safety relief valve sitting on top of boiler. Will provide the 1st floor purge data and check gate drain valve for 2nd floor over weekend. Keep you posted. Truly appreciate all the help. Thank you

hot_rod

Yikes, 5 pumps pumping at the PONPC. That will keep air removal an on going problem.
Less than ideal air purger and location.

EBEBRATT-Ed

If your feeding the boiler at 27psi for instance and the rad is 20' up the highest pressure you should get on the second floor is (20/2.31)=8.6PSi which is deducted from the 27psi or 19.4 psi. It does not get added to the 27 psi.