Boiler flooding with zone valves

JRenzoni

Hello all,

I have a situation I am looking to get some feedback on from the steam masters. My company just replaced a 5 section Weil McLain steam boiler (80 series) at a church. We took out a 5 section 80 series and put back the identical boiler. The existing system was retrofitted at some point in time with zone valves which broke the upstairs and downstairs into 2 separate zones. The zone valves have not been functioning for years and both were fully open to supply steam to the entire church on a call for heat.

The pastor at the church says that the zone valves previously worked going back 10 plus years but failed at some point and were just left open. That said, when we did the boiler replacement we installed new zone valves.

Some more information on the system… It is a wet return system. Most of the radiators are 2 pipe but there are a few that are 1 pipe. There is a check valve in each of the wet returns where they enter the boiler room. These checks were existing and we left them. There is no condensate/boiler feed tank and pump. We replaced most of the radiator vents as well as all of the main steam vents.

The boiler we replaced was piped incorrectly with a 2" supply header. We replaced with 3" header, equalizer and hartford loop to manufacturers specs. We have an automatic water feeder controlled by the first low water cutoff currently set to a 30 second delay.

Now for the symptoms we cannot seem to overcome. When the boiler is operating with the zone valves in play we are getting excess water and flooding at the boiler. Very little to no water hammer though which is strange but every 2 days I have to empty 10-15 gallons of water from the system to bring the level back to normal. The feeder is also adding 10 or so gallons of water to the system every 2 days.

As a test I disabled the zone valves and let the system run with both zones fully open. The system ran for 5 days without any flooding and the feeder never added water to the system. Worked great.

Started researching and found that zone valves wreak havoc on systems that were not designed for them. An article I found here on heating help stated that a 1/2" bypass pipe over the top of each zone vavle may fix our problem. We added the bypass pipe and ran the system that way with the zone valves working and still getting a flooded boiler.

Does anyone have any suggestions and/or advice on something to try? I am reading that check valves are not needed on wet returns. Thinking about removing those and seeing if it makes a difference.

What has me stuck is the claim that these valves previously worked with an identical boiler and now they don't. I added some photos of the new boiler for reference. Thanks guys!

clammy

I think i would have used a different method in the near boiler piping and the take off for the zone valves . Generally each steam main gets its own tee and not from the location that you have chosen usually prior to the drop for the eq not at that location . Personally i would have chose to put the zone valves up higher then that location .Usually a condensate drip is installed after the zone valve as to lessen the chance of condensate having no where to drain and possibly causing water hammer. If i was installing a auto feeder i would set it auto feeder on a longer delay .I would also remove the check valves on the returns . What is the height of you header personally i would have made the riser as high as i could but this is me . I see you have two lwco one of which is controlling your svx auto feeder one is operational and one should have a manual reset . Usually not that i do a lot of 80 series boilers but when using a electronic lwco i would opt to use a electronic lwco instead of a mech to control a electronic auto feeder but this is me . I would again set the feed delay longer and possible spend a few hours to see exactly what is going on as the unit fires and goes through a whole cycle . This may be related to thermostat set backs and slow return due to trying to over come a large set back or a completely cold system . Aside from that nice pipe work nice and neat . Don't take any of my advice the wrong way . on a side note i personally would have done a 4 inch header and like i had stated mounted the zone valves up higher and yes on the horizontal but not down low where they are and would have piped a drip on the outlet and piped into the wet return which is usually how it done . I personally stay away from zone valves on steam unless larger systems using condensate pumps and a boiler feed set up this type of set up usually always seem to be mostly issue free for the most part from what i ve come across . It seems that most zone valves on steam where installed to either balance out a system or save money either way there's usually some price to pay to get it all working happily which in some cases comes back to why they where installed . I never really seem a zone valve get a by pass but i don t claim to know it all just a little bit and i really can not see it doing anything except put steam into a main w no drip so that condensate can build up and cause hammer . Agian is that header at a min of 24 inches above the water line ? Can u post a pic of the 2 risers and a bit more of the boiler room

peace and good luck clammy

EBEBRATT-Ed

When the zone valves are closed there is no pressure in that steam main so it can't push the water back to the boiler. That's why you are flooding.

The only fix is a boiler feed/condensate tank and probably a lot of steam traps.

Thats big $$$$

Only choice is to abandon the zone valves and balance the system as well as you can.

You going to have water collecting at the zone valve outlet that can't possibly go up hill. Its going to pound and hammer.

Steam is a whole different animal. If done wrong it will never work.

Jamie Hall

Zone valves on steam systems… tricky.

There are two problems that come into play here. Well, more than two.

The first is that condensate must have a way to return to the boiler from the zone which is closed — and from the location of the zone valve. Therefore there must be a drip to a wet return on BOTH sides of any zone valve.

Second, on a two pipe system there are at least two distribution pipes and, commonly, three: the steam main, the dry return, and the wet return. The zone valve goes on the steam main, obviously. But not on the dry return or the wet return. The dry return isn't really a problem. There is a small joker there, though, as the steam main will need a vent or a crossover trap going to the dry return before the zone valve. The wet return, also, has no valves on it (lose those check valves) — but there is a potential real problem here. Note that the dry return is at atmospheric pressure. Note that the steam main downstream from the zone valve is at atmospheric. The wet return is not — it's at boiler pressure. What does this mean? It means that water will try to back out of the boiler into the wet return — and up into the dry returns and the steam mains downstream from the zone valve. What is the solution? Simple, but not always obvious — the boiler cutout pressure must be set low enough so that this doesn't happen. The maximum cutout pressure your system there will operate properly at is easy to find: find the lowest steam main or dry return and measure the distance from it down to the boiler water level in inches. Divide by 30, and that's your cutout pressure (it could be less — but it can't be more) (incidentally, that works for any two pipe system — zone valves or not).

A third potential problem — I hope those new zone valves are full port? If not, the heating downstream from them may not be all that good.

JRenzoni

https://forum.heatinghelp.com/discussion/comment/1848685#Comment_1848685

Clammy,

Thank you for your advice and input. The header is above the minimum 24" over the water line. I was thinking along the same lines of removing the checks and installing drips after the zone valves. That was going to be my next attempt at a fix but I can't keep throwing time and money at this if it wont solve my problem. Ugh!! I don't have anymore photos right now of the risers but can get some. I was also advised by another tech to increase the delay on the auto feeder so I will do that as well. Thank you for your help.

JRenzoni

https://forum.heatinghelp.com/discussion/comment/1848689#Comment_1848689

Hey Ed, Thank you for your input on this. My fear is that the boiler feed tank is probably the only solution here and I believe you are confirming that. The system runs well with the zone valves fully open so for now I may have to just live with no zones until we can figure out something for the feed tank. Thinking about the drips after the zone valves as well to help. Thank you.

JRenzoni

https://forum.heatinghelp.com/discussion/comment/1848691#Comment_1848691

Jamie, thank you for your input. I think the drip leg after the zone valves is needed as you mention. Still chewing on the cut out pressure portion of your response. Thank you.

EBEBRATT-Ed

The zone valve drips can go in the wet return or directly into the boiler return.. You need the drips downstream of the valves for sure because of the risers.

I would skip the drips at the valve inlets any condensate there will be minimal and will either drip back into the boiler or drip into the new drip on the valve outlet. Its only a few feet of pipe so it will not be much. that is what it is doing now with the valves left open.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1848709#Comment_1848709

This is what they were tying to solve with the check valves but is created other problems because the water has to stack up to a height sufficient to open the check valve before the water returns to the boiler. My completely non-profession opinion is remove or take the guts out of the check valves and run the boiler at as low a pressure as possible, ideally under 8 oz or so but les than 1 psig. This will work as long as it isn't using steam to lift condensate somewhere or something like that. If you have sized the boiler properly it should only build pressure when one zone is off.

The Steam Whisperer

I just double checked, Weil requires a 4inch header on the 580 boiler. 3 inch can only be used on the 380. Also, having a small 2 inch supply directly off the top of the header is likely pulling water up off the bottom of the header into the supply. However, these things are probably relatively minor.

What you need to look at is the height of the dry returns above the water line. Since the dry returns should have no pressure in them and should be vented to the atmosphere ( unless this is a naturally induced vacuum system), for every 28 inches of height, you can have a bit less than 1 psi of boiler pressure.

I.E: the lowest dry return is 40 inches above the boiler water line. 40inches / 28 inches = 1.43 psi. If you are running 2 psi max, the water in the return drips will back into the horizontal dry returns. You also need to check for this same dimension for the drips from the steam main into the wet return. If one zone is operating and not the other, the off steam main has no pressure in it so the water can back up into the steam main.

delcrossv

Could the combination of water in the dry return drips and the mains drip with the valve closed be enough to trigger the LWCO?

mattmia2

https://forum.heatinghelp.com/discussion/comment/1850144#Comment_1850144

read what @The Steam Whisperer said. Since there is no steam in the off zone there is no pressure from the boiler in the mains so the pressure in the boiler pushes the water up in to the zone that is off.

delcrossv

https://forum.heatinghelp.com/discussion/comment/1850145#Comment_1850145

Exactly. And the dry return drips too.

Question is: could that volume of water pushed up the drips kick on the autofeed to add water?

Seems possible...

mattmia2

If the boiler is allowed to run at a couple psig it could easily be pushing the water in to the lower emitters.