Advice on missing F&T traps

Mrmarky

Hello hello-
I’m working through pretty bad water hammer on a newly acquired 17 unit apartment building. I have a 2 pipe steam system and have replaced the thermostatic traps and properly pitched the radiators in each unit. Still hammering... started to trace all the steam mains and condensate returns when I had my aha moment. It seems all the f&t traps have been removed at the end of the mains at some point. Steam is moving vertically direct into the condensate line. It appears that one f&t trap has been added at the end of the condensate line and I understand this won’t work. My question is how should I pipe the new f&t traps into my system.. the mains run horizontal to the basement wall where two steam lines run vertical to the above floor radiators and one line flows down vertical directly into the condensate line. Can I use just a f&t trap or is a strainer and full port valve necessary? Where should it be piped in? I will try to add a picture

Mrmarky

Pictures below of two of the mains in question

EBEBRATT-Ed

You may or may not need F & T traps. It depends on how the system is piped.

If you have a boiler feed tank or a condensate pump then yes you absolutely need F & Ts.

If you do not have a feed tank or condensate pump and all returns go back to the boiler then you do not need F & Ts

But, the drips from the mains that drop down must go into a wet return line that is below the boiler water line.

So basically we need more information and pictures to make an assesment.

And if the drips from the mains tie into a wet return you still need to keep the steam pressure low to avoid condensate backing up into the steam mains

Mrmarky

thanks for the feedback.. there is a condensate pump on the end of the condensate return

Mrmarky

Can a vertical thermostatic trap be used in the situation?

Steamhead

@Mrmarky , I'd bet that condensate tank and pump are not needed. Most aren't, but we still find a lot of them. The Dead Men liked gravity-return because it was simple and had no moving parts.

Your system probably never had traps on those drip lines- if the return was always filled water (a "wet return") the water kept the steam from entering. Adding the tank and pump eliminated this water seal, causing the banging.

Some installers place a large F&T trap at the inlet to the condensate tank, but that only makes things worse.

Where are you located?

Mrmarky

@Steamhead , thanks for the response... I’m located in Rochester NY. It’s been difficult to get a straight answer from anyone locally.. Hard to tell what’s original and what’s not. It def has a pump and from what I have experienced the hammering is happening in the wet return. Part of the wet return has a small leak that we will be repairing, steam is hissing out of that leak making me believe there is a large amount of steam making its way down that return. If in fact the pump was added some years ago and eliminated the water seal do I have the right plan in place to add traps at the drips?

retiredguy

Has the boiler been replaced recently? If it has, that may explain a lot about how the system returns are now piped. There is always a right way and a butchers way.

Mrmarky

@retiredguy it isn’t original my guess is 30 years old or so. The down pipes certainly look like they are much newer judging from the picture I posted with insulation removed. My feeling is it has been worked on by some hacks over the years who made modifications thinking they were doing the right thing.