Replacement Dunham traps

nicholas bonham-carter

Would anyone know if the existing spud, and cover/element for an original 1913 Dunham 1 trap will mate up to a new Mepco trap?

2nd question: What choices are there for steam boilers using push nipples, as opposed to rubber gaskets, in the 175,000 BTU's? Thanks--NBC

Steamhead

Not sure about the trap

but there's a fairly good chance at least the cap would work.



There are plenty of boiler options. Oil or gas?

nicholas bonham-carter

Push-nipples

I am thinking about a pair of gas atmospherics, as there are not too many burner men around here, and the time delay involved with lighting off the lag boiler could be a problem.

If I want to make some experiments with running this old Dunham system in a vacuum, then I was a little worried about the effect of vacuum on any rubber gaskets, as they were designed to resist positive pressure, and not forces from the other direction.

I think SlantFin use push-nipples, but is there anyone else in that 175,000 BTU range?--NBC

JStar

Boiler

Peerless 63-04. 177,000 input

nicholas bonham-carter

thanks for the information

just what I needed to know!

who is Mr. Thatcher then?--NBC

Dave in QCA

Dunham Traps

Hi Nicholas, The caps for the old dunham traps will not mate up with the new 1-e, 2-e traps. The old dunham 1, 2, and I think there was also a 3, are very large diameter and it seems that Dunham redesigned the traps by the 1940s. All of the 1E traps from Dunham, Dunham Bush, or Mepco would be the same. In my property, the radiator traps were originally 1909 #2 traps for 1/2" pipe. That seems strange I know, because as I understand, the #1 traps was for 1/2" and the #2 trap was for 3/4", but several of my old original traps had caps that said No. 2 on them.



Many of the traps in the building had been replaced with 1E traps. They are smaller but the use of a pipe extension fitting allows them to fit perfectly. The 1E traps that had failed.... 95% of the bunch, I repaired with replacement discs and or replacement caps with discs. You can usually find someone selling them on ebay for real cheap!



What I did to repair the old #2 traps was use a Barnes Jones cage unit. The have cage units for the old original Dunham traps, along with replacement caps and gaskets. They work great. The cap has to be replaced in order for the cage unit to be held in place properly.



Regarding boilers, section seals and vacuum, there is nothing to worry about vacuum. The way the Weil-McLain seal is held in place is bi-directional. It works for pressure or vacuum. I have had my system running on a WM 680 down to 9" Hg Vacuum with no issues at all. But, if you want a boiler with push nipples, in addition to slantin, there is Peerless and Burnham, perhaps others too.



Ooops! I just re-read and see that Joe already pointed you to the Peerless. As I recall, you're running a large peerless in the big building.



Have fun with your dunham! I have had difficulty in staying in vacuum, but once the air is out of the system, subsequent cycles have little if any air to vent. I am sure I have a few leaks yet, but have chased down most of them.

JStar

Welcome

He's a ghost. Truth is, I've always liked the look and sound of Thatcher whenever I saw it on the front of a boiler or furnace. I'm now "borrowing" the name.

nicholas bonham-carter

Not a ghost!!!!

A dead man!--NBC

nicholas bonham-carter

Reviving this thread

Now for another question on vacuum systems. As the water will boil at lower temperatures, does this not interfere with the trap temperature setting? In other words, if the trap has been designed to close at 210deg for use in a standard 2-pipe system; then won't the lower temperature of a Dunham vacuum system allow the cooler steam out into the returns., and maybe even out of the air eliminator?

Maybe this is why the crossover traps from Dunham were different from the standard 1E traps.--NBC

Dave in QCA

Dunham Traps on Vacuum

Nicholas, you have touched on a subject that mystified me for quiet some time. Does a thermostatic trap operate properly on vacuum and if so, how the heck does it do it?



First, your observations that the early Dunham systems did not use the 1E trap for crossover. That is correct, they used the the Dunham Air Line Valve. That device was actually a small version of a 1E type trap and the same thing as a paul type trap. In addition of it being used as a crossover trap at the end of steam mains, it was used on vacuum one-pipe systems as a retrofit, just like Paul systems. I supposed it worked fine because often in coal fired systems, steam was slow to build. Whatever the case, my guess is that Dunham discovered that they had a real big problem with unbalanced distribution, especially on partial steaming cycles. Thus, they started using "balancing plates" or orifices to even out and regulate the steam at the entry point of the radiators. They still used traps so the orifice openings must have been larger than they would be on an truly orificed system. About the same time, according to my reference books, they stopped using the air line valve as a crossover trap and instead started using the 1E. Of course, a 2E would be even faster.



VACUUM ? If you look at the cap on a 1E trap, you will see that it is rated from 25" vacuum to 10 psi steam, actually some early Dunham 1E traps are marked to 25 psi steam. How does it work? That steam at 25" vacuum is not very hot at all!



It took a long time for me to wrap my head around it, but eventually found an explanation somewhere in one of the Dunham books, or at least I think that is where I found it. Here it is. You have to realize that the thermal disc in the dunham trap is flexible, somewhat like a balloon. When the temp of the disc is hot enough, around 180 or 190 at atmospheric pressure, the alcohol will vaporize, causing an increase in pressure inside the disc, therefor expanding the disc and closing the trap. Now, if the the system pressure is 10" Hg vacuum, the flexible capsule will expanded because of the low ambient pressure, transferring the forces of the vacuum to the contents of the disc as well, and lowering the flash point of the alcohol inside the disc. Thus, the closing temperature of the trap adjusts according to the surrounding pressure/vacuum so that the closing temperature is lower than the actual temperature of the steam at that same temperature.



Nicholas, I forget about the detail of the Dunham system you're working on. Does it have an air eliminator? a return trap? any other original boiler room apparatus, such as a differential controller, etc?

Pumpguy

Thanks Dave,

for this explanation.  I too had wondered about this, and your explanation makes it all very clear.