Banging single pipe radiator: Is this worth trying before more drastic measures?

condensationpoint

I apologize for the lengthy post in advance.

I have a situation in which a small 2nd floor steam radiator on a single pipe system is banging quite a bit at the beginning of the heat cycle then gurgles/boils once hot. It is probably the furthest radiator from the main but is not the last in line, the radiator is sloped correctly, the valve is fully open, it has a newer adjustable vent set fairly low (3 out of 9), and the only times it doesn't bang is when the heat has not been on for an extended period of time (I'd guess 24 hours or more). I've tried to lift the radiator / supply but it won't budge more than a sixteenth of an inch or so and I'm loath to use more force lest I break something below the floor. The main is well vented.

My best 4 guesses at this point are:

1.) The supply pipe is sagging in a horizontal stretch under the floor letting condensate collect and pool,
2.) The supply pipe is undersized (the steam valve is 3/4 inches and I assume the supply is too, but am not positive. There's an elbow that might be a 1 to 3/4 reducer. - I need to take it apart to check),
3.) The supply pipe is partially obstructed with crud, and/or
4.) The reduction bushings (there are two) to get from the radiator's native 1-1/4 inch bottom hole down to the 3/4 inch steam valve is resulting in water pooling where it steps up at the bottoms of the two bushings.

The supply pipe emerges vertically from the floor just an inch from the wall. A 90 degree fitting then leads to the 3/4 inch steam valve oriented horizontally in order to allow the radiator to fit next to the wall. (Without this jog of several inches, the wall would require an inset cut into it in order for the radiator to fit where the supply pipe emerges from the floor.) The valve then goes to a pair of bushings (presumably 3/4 inch to 1 inch, then 1 inch to 1-1/4 inch) to mate to the radiator.

I am considering the following before resorting to either removing the radiator entirely or opening up the floor. I want to try replacing everything from the point where the pipe emerges from the floor to the radiator with 1 inch or even 1-1/4 inch fittings and valve. I believe this would require a 90 degree reducing fitting to make the jump from the supply (which I assume is 3/4 inch) to a new 1-1/4 valve and then directly into the radiator without any bushing needed. This would seem to eliminate the possibility of any bottlenecks between the vertical supply (which presumably runs horizontally under the floor before dropping down against a back wall to the main) and the radiator itself. This would create a bottleneck at the 90 degree reducer, but the condensate would be falling vertically at that point and unlikely to collect there.

Could you please advise if this approach sounds particularly stupid? I simply don't know if increasing the diameter of everything between the narrow supply pipe and the 1-1/4 inch radiator hole is likely to cause a new problem while attempting to address an existing problem.

Regarding potential obstruction (guess 3), would just pouring a lot of water down the supply pipe and then blowing into it like a balloon have any chance of clearing it of crud in the horizontal run?

Any advice or insight you could share would be appreciated!

Jamie Hall

The problem with replacing the radiator valve is the connection to the radiator itself. That is a union between the valve and the radiator. Getting the bushings out of the radiator and getting a new spud in there to match the new valve could be rather tricky.

That said, those bushings -- concentric, I presume -- are a rather poor way to do the job, and they surely are holding water -- and they may be part of, or even all of, the problem.

But... I'd be much more suspicious of the horizontal run under the floor, particularly if it too is small (like 3/4 inch) and the horizontal section from the riser to the valve. Under the floor is the most likely. From what I'm reading, it seems to me that the banging which tends to stop when the radiator starts to heat (is that correct?) is steam in that horizontal line pushing condensate in that line along until it hits the elbow going up to the riser; the gurgling is the condensate from the reservoir trying to make it back.

An obstruction -- your number 3 -- is sufficiently rare on a steam line that I'd look at slope problems first.

EBEBRATT-Ed

What you are planning makes perfect sense. What else can you do? The piping under the floor is most likely the problem but it's concealed so you would have to tear up a floor or ceiling. Try your approach first and hope for the best

NTL1991

I think you're on to it...

Do you have an EDR rating of this radiator? Typically the valve is one size bigger than the supply piping. That probably means at least a 1" supply valve, or maybe 1-1/4" depending on your exact EDR.

An eccentric bushing or reducer would prevent a lot of condensate from puddling. That pair of bushings sounds like trouble... I'd go full size from the valve into the radiator.

condensationpoint

Thanks for the input! To highlight my ignorance, I'd not heard of EDR before, just looked it up for the radiator in question and it's 16. Also, it looks like the spud (AKA larger of the two bushings?) has plumber's tape on it where it threads into the radiator hole, so I have some hope of being able to unscrew it from the radiator.

New England SteamWorks

From your description it seems obvious that the radiator, it's position, and it's piping, -are not original.

9 times out of 10, when I see this, -it bangs. I bet it's piped in 3/4 copper. And I'd bet further it's in a kitchen or bathroom that was renovated.

condensationpoint

Yup, it's in a kitchen. It does appear at least to be iron pipe, but it's clearly a 3/4 inch riser going into the floor, and almost certainly 3/4 inch pipe running horizontal to the original riser. I'm leaning towards trying my plan as described above and keeping the adjustable vent set very low to see if that helps, but it's clear that the primary problem is in the pipe under the floor.

Is there ever a valid reason to use pipe smaller than 1 inch in a single pipe steam system?!

At least the riser from the basement appears to be larger diameter (1-1/4 or 1-1/2), so if I ever decide to rip open the kitchen floor or ceiling below, I'll likely not have to replace the pipe all the way to the basement.

BobC

I have a small sunrad radiator (EDR of 17.5) in my bathroom that was installed about 40 years ago before I moved into this castle. This was done when they updated the bathroom and that benighted installer piped the entire run in 1" copper - about 25 feet. That hack also cut some of the 2x8 joists down to 2" to make his job easier, I have since sistered those with 1/4" plate steel. I have a MOM #5 vent on that radiator.

The run is well sloped at the expense of the floor joists and runs just fine. TLAOSH tells us a 1" feeder is good for an EDT of 28 and a 1=1/4" is good for an EDR of 55 so my WAG would be that a 3/4" feeder would be good for about an EDR of 15. All of this is for a counterflow situation in the feeder pipe where there is no drip for the condensate. As I said this is just a guess on my part.

Bob

condensationpoint

Thanks Bob, those metrics are useful. Graphing your 55 and 28 EDR data points with the area yielded by their respective pipe diameters, and extrapolating suggests that a 16 EDR radiator should have a pipe cross sectional area of about 0.6 square inches. I believe a 3/4 inch pipe only yields a cross section of 0.44 square inches.

New England SteamWorks

condensationpoint said:

Is there ever a valid reason to use pipe smaller than 1 inch in a single pipe steam system?!.

No.

EBEBRATT-Ed

Just not enough room for the condensate and the steam to pass each other

condensationpoint

To wrap this discussion up, I removed the fittings with ease, but when looking into the radiator I realized that upsizing to a 1-1/4 inch valve with a 90 degree reducer to the 3/4 inch riser wouldn't serve me well. My concept had been that doing so would at least minimize water pooling in the radiator behind the existing concentric bushings (1-1/4 down to 3/4), but I saw that the inside bottom of the radiator is uneven between sections. This is surely obvious to anyone who's looked inside a radiator with a light before, but the rise between each section is nearly the same as the rise from the bottom of the 1-1/4 drain hole to the 3/4 inch valve, so doing away with the bushings and upsizing to a larger valve would really only address fully draining the very first section. A spoonful or so of water would still pool at the bottom of each of the remaining nine sections of the ten section radiator.

For the time being, I have managed to find a sweet spot with the adjustable air vent that allows steam into the radiator but not so fast that it hammers or vaporizes the bit of water at the bottom of each section causing instant expansion and banging.

The proper, but drastic, solution is to replace the 3/4 pipe with correctly sloped 1 or 1-1/4 inch piping.

the_donut

Did you try running a tube and sucking out the sludge while you were in there?

condensationpoint

No, the radiator was pretty clean. If you mean the supply pipe, no, that didn't occur to me.

Fred

condensationpoint said:

No, the radiator was pretty clean. If you mean the supply pipe, no, that didn't occur to me.

There won't be anything in the supply pipe. You aren't going to fix it unless you change out that 3/4" valve and supply pipe.