Big Mouth Crossover Trap Install

Steamhead

Part of yesterday's job was a crossover trap upgrade on a Hoffman system next door to @Koan 's house. Two 2-inch mains, one about 20 feet long and the other about twice that. Both had Hoffman #18 crossovers that appear to have failed open. The vent at the Differential Loop is a Gorton#2.

The long main got a Big Mouth:



and the short one got a 122A:



Both mains vent quickly, but the long main still takes about a minute and 20 seconds longer to fill with steam than the short one. I'd bet the lousy near-boiler piping is at least partly responsible. But it's a lot better than it was!

Sailah

I think that's the first pic of a Big Mouth Crossover trap in the field.

nicholas bonham-carter

Why not a bigmouth on each one?
The lack of pipe insulation is not helping either!--NBC

Koan

@Steamhead @Gordo Thanks for taking good care my neighbors!!

Steamhead

nicholas bonham-carter said:

Why not a bigmouth on each one?

Because we want the steam to reach the ends of both mains at about the same time. There's plenty of venting speed but balance is just as important.

nicholas bonham-carter said:

The lack of pipe insulation is not helping either!--NBC

That's on the list.

Steamhead

Sailah said:

I think that's the first pic of a Big Mouth Crossover trap in the field.

Feel free to use it, as long as you attribute it to us. I have a full-resolution version if you want it.

The Steam Whisperer

The G#2 is the bottle neck, so a bigmouth or two at the diff loop should help. Also, I have used some bigmouths at the loop with a low cracking pressure check valve ( apollo 61-104-A1) with great results. The systems are pulling 10 inches vacuum after boiler shut down, and the added advantage is that there is almost no need for air venting once the vacuum is charged on an initial cycle.... no need for big crossover traps or main vents!

Steamhead

Interestingly enough, we don't hear any air rushing out of the Gorton. That's what makes me think the near-boiler piping is the bottleneck, or maybe there really is no bottleneck since this is basically a glorified rowhouse. I think the boiler is 375 square feet EDR or so.

Koan

@Steamhead ... I can hear air coming out of the Gorton #2 on ours , we have a bit more interior space but our boiler has twice the EDR! I knew of the previous owners of that house - they never did much as far as maintenance so it would not be surprising a lot would be required.

Steamhead

Koan said:

@Steamhead ... I can hear air coming out of the Gorton #2 on ours , we have a bit more interior space but our boiler has twice the EDR! I knew of the previous owners of that house - they never did much as far as maintenance so it would not be surprising a lot would be required.

ISTR your boiler is considerably oversized.

Harry_6

I noticed that the Big Mouth box says it should be mounted with the tail piece down. Any idea why? And do I assume that the "tail piece" is the inlet "spud," which is detachable and tail-like, or the outlet, which being the outlet is the "tail" as far as direction of flow goes? -H

Steamhead

That applies when you use a Big Mouth as an ordinary air vent rather than a crossover trap. The reason is so any condensate in the Big Mouth can drain back to the steam main.

Jamie Hall

I wonder just how much of the difference in timing on the two mains has to do with simply needing to heat up more iron. After all, the steam simply can't move any faster than it can heat the pipe, assuming the vents or crossovers are at least big enough to let it move that fast.

Also not really surprised you don't hear much air at the #2 at the loop -- I don't either (that's how Cedric is set up).

BobC

On a run from cold steel there would be a substantial difference but if everything was still hot and the piped insulated not so much.

That is one reason when I had to have an AC installed I paid the extra for an efficient heat pump (COP of 3), on mild winter days the steam stays off and the HP carries the load.

Bob