Vapor Steam Help

tmarts

Hello Everyone,
I am a contractor from Ann Arbor Michigan and am having some trouble getting this system running properly. I am getting banging after the boiler has been running for some time. A few years ago 1 boiler was replaced with 2 boilers, 1 for each end of the house. I believe at that time a boiler feed pump was added. Instead of trapping the mains they kept the water seal by creating a false water line before the condensate tank. I am not sure if this will work this way or if F&T traps needed to be added. Since the pictures were taken both boilers are running on a vaporstat set for 8oz cut out and there have been no complaints with not heating, just the banging pipes coming from the mechanical room. All radiator traps have been repaired with B&J cage units. Please let me know your thoughts and any suggestions. Thank you ahead of time.

PhilDavid

Are both boilers sharing the same boiler feed pump? If so you need two... one for each boiler

Jamie Hall

First off -- do the two boilers serve completely separated systems? I hope so... otherwise things get very complicated unless they are right together and carefully piped and controlled. If they share the wet return connection do not have a steam equalizer between the headers, you may need check valves to keep steam pressure in one boiler from backing water into and flooding the other.

Second -- false water line and condensate tank(s). Why? If the boilers were installed with their water lines too low -- not uncommon with installs where people weren't paying attention -- I can see that a false water line might be needed. I'll get back to that. But condensate tanks? No. Nor condensate return or boiler feed pumps. They cause more problems than they solve.

So... likely the first thing you need to do is to trace and locate all the wet returns and water seals between steam mains and dry returns, and make absolutely certain that they are all below the operating water line -- false or otherwise. If they are not, that needs to be fixed -- one of the more common causes of water hammer is steam getting into a dry return where it doesn't belong, and that usually shows up late in the cycle. Look in all the dark corners. Indeed -- trace every single pipe!

Then having done that and fixed any problems you find, you should be in a position to repipe, bypassing the wet returns around the condensate tanks and see how far you've gotten.

You also need to consider venting. In many vapour systems -- not all -- the steam mains were vented with crossover traps into the dry returns (condensate was handled with drips into the wet return). If they are there, make sure they are operating properly. If they are not there, check carefully to see if they had been once and been removed. I that is so, replace them. In any event, the dry returns must be vented very completely. Clearly if there aren't crossover traps and never were, the steam mains must also be vented thoroughly.

In my humble opinion, F&T traps are a nightmare. They should never be required, nor present, on a properly piped and vented vapour system.

tmarts

@PhilDavid - Yes there are two pumps on that tank, one for each boiler
@Jamie Hall - The condensate receiver was already there when we took on the job. There were many problems with the original boiler installation we have been trying to fix. The boiler does serve seperate areas but the wet returns are connected in the boiler room all going back to the condensate receiver with the 2 boiler feed pumps. I have not seen any crossover traps. There are 6 pipes going into the wet return. 1 is from a remote condensate receiver that is on the other side of the building, 3 are steam mains 2 of them do not leave the boiler room and 1 is a 1/2" line that is not vented at all, it looks like that one was added later and 2 are the dry return lines. There was an addition/renovation done to the house in 1958 and many of the existing radiators were changed to cast iron convectors. This was also when the first condensate receiver was installed. In the room with that condensate receiver are 2 F&T traps and also wet returns from the basement convectors. The prints shown are from that addition/renovation. At that time there was still only one boiler and no boiler feed pumps.

EBEBRATT-Ed

Looks to me like all the returns dropping down probably used to be wet returns and when they added the condensate pumps they became dry returns and that's where the banging comes in.

If I am correct you going to have to add traps to each return UNLESS you have radiator traps. You may have bad radiator traps causing the banging

Need radiator pictures
And more information

Controlling the water level in two boilers at different locations with maybe different water lines can be a major issue.

Do you have condensate pumps or boiler feed pumps. There is a difference?

tmarts

@EBEBRATT-Ed - I believe that is why they have the return to the condensate receiver coming up and then back down to try and preserve that water line in the returns (picture 3). Just to clarify, there is 1 condensate pump in a pit on the other side of the building that pumps into the wet return and then there are 2 boiler feed pumps connected to the condensate tank (picture 3) that feed each of the boilers independently. The water level is always the same in the returns. All radiators and convectors have traps on them that have all been replaced with new cage units. Thanks for the help

Jamie Hall

Quite possibly right on why they have that wet return pipe going up and back down to the condensate tank. Problem is, unless I'm missing something, that pipe at the top isn't connected to the steam main, and to function properly as a false water line it needs to be. The way it is set up it is a siphon (as I say, unless I missed a pipe) and what will happen is that when the condensate tank is pulled down, it may pull water from the wet returns -- with, potentially, unfortunate results on the drip seals.

tmarts

@Jamie Hall - That is what I was wondering. On the other side of the water seal is just the tank which is open to the atmosphere via the vent. The steam mains are 2 of the vertical pipes you see connected to the wet return that goes around the boiler room.

Jamie Hall

This is sort of a WAG, but i wonder if at times that wet return gets just dry enough that some steam can sneak in there -- that would give you a lovely hammer!