Mystery 'U's\dips where Steam Mains meet Dry Returns, (and Water Hammer)

Tom8o · November 9

I've learned a lot reading many of the posts on this forum, thank you all for your contributions.

I insulated all the pipes in my basement in 2019 and did not take any good photos before then. A photo below is blurry and shows the loop\dip of my 52' long line (Main + this 'U' + Return). Another photo also circles the U in red and is after I insulated. Three photos show my 81' long line's U circled in white.

Are these 'U's called water\wet seals?, or traps? If there is water in it, how is it not a cause of water hammer since I've read over and over that steam colliding with water causes water hammer?

My system is experiencing water hammer ("mid-cycle" I believe) only on the 81' line, not the 52' line, and I have hope that that will be fixed after I properly pitch the pipes, then increase the venting. Presently, the 81' line has a Dole 3B at the end of its Main and a B&J\VentRite 86D at the end of its Dry Return, and the 52' line has a Dole 3B at the end of its Main and a VentRite 35 at the end of its Dry Return.

Back to the U: are there any components in the U?, or is it merely pipes and fittings? Is there any servicing I should to do to it? If requested, I will take off the insulation and show a better photo.

The 81' line has 5 two pipe convectors and 1 one pipe convector which is in a renter's room, so I'll need to coordinate with them to see if the 1-piper has its own vent.

Jamie Hall · November 9

Those are nowhere near deep enough to be water seals — water seals must drop at least 28 inches per psi differential working pressure in the system.

Are they just a plain loop, or is there by any chance a thermostatic trap buried in there?

EBEBRATT-Ed · November 9

My questions are the same as @Jamie Hall a trap on that drip. Also the "return line" if thats what it si going off at a funny angle is that a radiator return? Rads 1 pipe or two pipe?

Guess ing two pipe.

Tom8o · November 9

Here's a photo of the 81' line's loop\U with the insulation cut open. Looks to me like all it is is a plain loop. There is a plug on the bottom (should I drain it sometimes?) and towards the top is a union (might this be useful when correcting the pitch of the main line and return line?).

Ed, which photo are you referring to? The second red circled photo? Or the first, second, or third white circled photo? The 81' line (white circles) has 5 two pipe convectors and 1 one pipe convector. The 52' line (red circles) has 5 two pipe convectors.

Tom8o · November 9

mattmia2 · November 9

maybe that loop was far enough down with an old boiler with a much higher water line

Steamhead · November 9

Either that, or someone replaced wet returns with dry returns.

@Tom8o , is there an air vent both before the loops (as I see in the pics) and at the end of the line where it drops to the boiler? If so, steam is probably pushing through the loops and banging as it tries to reach the end-of-main vents.

mattmia2 · November 9

https://forum.heatinghelp.com/discussion/comment/1871613#Comment_1871613

I see vents on the dry returns at the boiler so unless that return drops down and becomes a wet return before the boiler, there is a second vent.

Jamie Hall · November 9

On your water hammer question — it isn't steam meeting water which makes the water hammer, it is moving steam encountering just enough water to make a nice wave and push it along until the wave meets an obstacle like an elbow or bullhead. Those U bends like won't hammer for one of two reasons: first, if there are no runouts downstream there's very little velocity so no hammer or, second and conversely if there is a big vent or radiator runout the steam velocity is high enough to effectively blow them dry.

Tom8o · November 10

@Steamhead if someone replaced wet returns with dry returns, why not join the Main to the Dry Return with a simple bend (two 90° elbows with a nipple in-between)? Is there a usefulness to the dropdown-dip and the plug?

@Steamhead yes, vents at both places on both the 81' & the 52' lines. The 81' line (white circles) has a Dole 3B (1\4"pipe) vent at the end of its Main before the loop\dip and a B&J\VentRite 86D (1\2"pipe) vent at the end of its Dry Return; and the 52' line (red circles) has a Dole 3B (1\4"pipe) vent at the end of its Main before the loop\dip and a VentRite 35 (1\2"pipe) vent at the end of its Dry Return. The 81' line bangs, the 52' line does not. For the 81' line, I have a Gorton D I'm going to add beside the Dole 3B. For the 52' line, I have a Gorton C I'm going to add beside the Dole 3B.

@mattmia2 the Returns are both well above the boiler's water level. At the end of the Returns, where they have vents (shown in the boiler photo) and then drop down vertically, the bottom of the Returns' pipes are 31.5" above the boiler's water level.

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I repitched the lines yesterday evening (some I lowered or raised with their hangers\straps, others I had to push down by hammering a piece of lumber between the pipe and the joist above), but the boiler hasn't fired since to test the new pitch.

The venting capacity of the VentRite 35 is 0.200ounces at 2OZ CFM. I don't know that of B&J\VentRite 86D, but it appears to vent more, and I don't know that of each Main's Dole 3B, but they appear to vent less. Should the Mains' vents have greater venting capacity than the Dry Returns' vents? (@ 2OZ CFM: Gorton D does 0.540oz, Gorton C does 0.450oz.)

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@Jamie Hall thanks for explaining water hammer. The 81' line had parts of the Main and the Return that were wrong way and I think I properly pitched them yesterday evening. So 🤞 no hammering during the next heating.

By "runouts" I think you are referring to pipes going to \ coming from convectors that branch off the Mains and the Returns. My system has both of those since 10 of my house's convectors are 2-pipe, and one is 1-pipe. So, there are runouts both upstream and downstream of the U bends.

mattmia2 · November 10

The water line in coal boilers was much higher than in modern boilers.

The vent at the boiler shouldn't be doing anything but possibly acting as a vacuum breaker. but much larger vents at the end of the main and replace the vents at the boiler with a vacuum breaker or plug them. Right now the steam will try to push through the water seal until it can get to the vent at the boiler and close it.

Jamie Hall · November 10

I am getting a sneaking suspicion that you may been knuckleheaded at some point back it the past. If you have two pipe convectors, the question becomes whether thay have traps on the outlets — or vents. If they have traps on the outlets, then they are expecting those returns to be dry - and at atmospheric pressure… and those odd U bends may very well have been much deeper water seals which someone decided they didn't need.

And your system will work a LOT better if they are restored!

Steamhead · November 10

@Tom8o , can you post some pics of your radiators? If they are concealed in cabinets, can you show at least one with the cabinet open?

Tom8o · November 11

Thanks @mattmia2 @Jamie Hall @Steamhead for your engagement.

My repitching of the 81' line's Main & Return the other evening has decreased (halved?) the number of water hammer bangs, so that's an improvement! I'll double-check my work and maybe adjust, or I may increase the venting at the end of the Main first.

@mattmia2 I'll add a Gorton D alongside the Dole 3B on the 81' line's Main and will see how that changes things, then may replace the Return's B&J\VentRite 86D with a cap. This is the first time I'm reading about a vacuum breaker, so I need to learn more.

@Jamie Hall yes, the 81' line connects to five 2-pipe convectors and one 1-pipe convector, on two floors. None of the 2-pipe convectors have vents nor traps that I can discern. See photos. The 1-pipe is in a renter's space and I can take a look in the coming days.

@Steamhead I've included photos of two of the 81' line's convectors. They're both on the first floor. All of my house's convectors are this style and I believe they all have this setup of internal fittings\pieces, except the one 1-pipe convector in a renter's space is something I'll need to get back to you about in the coming days.

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Question: is it equally important that the Main and the Return are sufficiently pitched downward? If I only have several inches of drop to work with, and I'm struggling to be confident about sufficiently downward pitch, then is it more important to prioritize sufficiently downward pitch for the Main versus the Return?

Steamhead · November 12

If those are Trane convectors, they probably have orifices cast into them. Otherwise, the traps may be in the basement.

mattmia2 · November 12

If there are not traps in the basement and they do have orifices built in, you need to keep your pressure very low or you will get steam in the returns through the convector.

The returns only need to be pitched in places where they are providing venting.

Actually, you do need the vent at the boiler because it is 2 pipe, that is how the emitters vent, through the returns.

Pitch won't solve your problem, you either need to make the water seal deeper or keep the differential pressure between the supply and return so low that it can't lift the water out of that water seal. You would need to be under about 6-8 oz/in^2 to not blow the water out of those seals.

Are there any devices near the boiler? This appears to be a vapor system that possibly lost the vapor specialties at the boiler.

Tom8o · November 12

@Steamhead @mattmia2 ,

yes they are Trane convectors. I see nothing resembling an orifice - just learning about them now for the first time and not sure what they look like (see search screenshot that doesn't show much re orifices).

I haven't seen anything in the basement resembling an F&T trap nor a Thermostatic Trap, based on photos of them from searching those terms.

My boiler has a pressuretrol honeywell pa404a above a pigtail on the LWCO, and I've read a lot of advice on this forum about installing a low pressure gauge - I've a 0-5psi gauge to install hopefully tomorrow.

Re water seals, will you point me towards a good diagram or reference about this topic? Not one of the many diagrams I've seen of steam heating systems shows a dip/loop/U at the bend where the Main joins the Return.

mattmia2 · November 12

get "the lost art of steam heating"

some models of trane convectors have an orifice in the cast iron body itself, there isn't really any sign it is there, you just have to know they are designed that way.

Jamie Hall · November 12

You won't see orifices — they are built into the radiation or installed as a thin shim with a hole in it or sometimes built into the feed vavle.

Most Trane systems operated in the vapour/very low pressure range.

If you don't have The Lost Art of Steam Heating you need it. If you do, you don't need Dr. Google.

Tom8o · November 12

Thanks again for your additional advice @mattmia2 & @Jamie Hall. I've ordered the book. I'm looking forward to learning from it more about:

my boiler,

the overall setup (e.g., attached devices, vaporstat necessity, etc),

piping (e.g., pitch prioritization),

my specific convectors (e.g., my model's features, okayness with partial opening of supply valves, okayness with fully closing some of the system's convectors due to another heating appliance in the house, etc),

venting (e.g., needed vent capacity for my system and pipe sizes), if the 1/4" tapping on the Main needs enlargement, etc),

removing or modifying the water seals,

how to reasonably remedy the water hammer.

Re Dr. Google: ChatGPT generates some good leads, but it is overly confident and hallucinates, so ... to the book you recommended I go!

Mystery 'U's\dips where Steam Mains meet Dry Returns, (and Water Hammer)

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