Venting 2 Pipe with cond pump vent not helping

JUGHNE

Working on a 1938 schoolhouse. 2 pipe system. 1973 Kewanee boiler 52.2 HP, 1,750,000 BTUH input.
There are 3 main steam runs. 2 of the 3" mains have zone valves that are not 100% shut-off. These two have end of main F&T H pattern design. They both are pretty well under water, just borderline to drain, was going to replace these with In line F&T pattern Hoffman's.

The real issue is where this air venting could go, usually the cond return pump vent, however 2 of the high dry returns tee together and go into the wet return of the condensate pump discharge. These two have a check valve after the Tee before entering the discharge line. The cond pump handles a third low gravity return. Pump discharge (has check valve in discharge line) is low below the water line and goes into a Hartford Loop. The 2 returns that are Tee'd together use gravity flow into the lower part of the discharge line.

So how would the air get out of these 2 high dry returns? This is piping done with the boiler change out of 1974. I have a hard time to imagine how this could have ever worked, maybe the 6 PSI cutout pressure pushed the air into the boiler, it couldn't get to the cond pump vent as there is a check valve in that discharge.

Water hammer is so bad I wanted to leave the basement, teachers said it does this every time it starts to heat their area, only lasts 15 minutes or so.

I have a capped 3/4 riser on each dry return just before the Tee/check valve. I have considered an antler for Gorton 2's on each. Mains are 120' & 150' 3" going down to 2". If all traps, F&T and rads, work properly would air vents ever shut?
In theory I could just use an open pipe??

Or I could put air venting ahead of new F&T at end of mains but still must do dry returns venting also.

Steamhead

Those F&T traps won't pass much air. How much lower are they mounted below the steam mains? If less than about a foot, your ΔP across the trap is pretty low, which can cause condensate to drain slowly from the main. This can cause banging.

Vent the dry returns first, with at least one Gorton #2 on each. This will maintain the dry return at about zero pressure, increasing the ΔP across the traps. See if this stops the banging.

Since the #2 has a float in it, it can close (at least partially) if water backs up into it. An open pipe can't do that.

JUGHNE

The end of main F&T's have very little drop fm the 2" to dry return. The typical 2" X 3/4" reducing 90 ell set at a 45 angle and then the in line F&T will just about establish the correct slope for return. Original F&T were Warren-Webster with closely spaced inlets & outlets. When they were replaced with Hoffman 53's (old H design-4 bolt cover), the slope was lost for return at that point and was requiring water to run uphill.

The 1938 Dead Men could have gotten more differential in elevation at that point as there is a lot of head room in the basement.

My 3/4" air ports could support up to 4 G2's each.
Are 4 G2 before the F&T and 4 G2 at end of dry return overkill?

Charlie from wmass

Not overkill.

JUGHNE

Now the 1974 boiler crew did the 2 dry return/tee/check valve drop into discharge of cond pump. Will I have enough pressure to get water into the boiler. There is about 7' drop from overhead horizontal return to floor water line/pump discharge into HL. Boiler water line is about 5'. Boiler sometimes floods just above sight glass during operation and when one zone operated there was a good flow of steam out of cond pump vent.

So it is obvious that things need attention. (14 degrees outside now).