Replace old style gas valve

bob_46

You don't need to buy a gage or manometer all you need is a piece of 1/4" tubing, a way to connect it to the manifold or outlet of the gas valve and an empty beer can . Mark the tubing every 1/2" , fill the can with water , hook up the tube to the gas and stick the other end all the way into the can, fire the burner and slowly pull the tube out of the can, notice which mark is at the level of the water when the first bubble appears. The distance from the end of the tube to the mark is the pressure in inches of water.

BobC

It is one of life's main corollaries that the moment you discard an item it will be urgently needed. If you don't believe me have a look in my cellar or my garage.

Bob

Tim McElwain

I have a whole training center full of controls. I have tons of brand new controls that I have been trying to get rid off but nobody wants them. They have never been used and are still in the boxes.

VDBLU

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I've got the new combination valve installed and operating. I clocked the meter again and got a reading that matched the earlier tests. I also had a combustion analysis done and it came in at 6.1% O2, 8.4% CO2, 37% excess air with a stack temp of 148 degrees. It shows a combustion efficiency of 87%. The instrument doesn't have a CO measurement so I'm trying to get the tests rerun with a different one to verify that it is also within range. How do these numbers look to everyone? Anything else I should do or have done?

Tim McElwain

I do not buy the stack temperature, it is too low and if it is correct it is unsafe. I have a feeling who ever took the test did not correctly measure the flue gas temp. It should be taken before the drat hood as close to the boiler as possible. Other wise you get a contaminated reading. That efficiency is also too high for that unit.

VDBLU

Tim

This is the hole:


And a longer shot to show everything:


Does that look like the right place?

I double checked with my meat thermometer and got a reading as high as 180 degrees. It varies a bit depending on how it's in the hole.

Tim McElwain

The net stack (stack temp minus room temp) should be around 350 to 450 degrees F. I would get a better way to measure temperature. The other numbers look good but the stack temp is way too low.

VDBLU

I thought you'd appreciate the meat thermometer . I'm still working on getting the tech back with the more expensive meter. I think I can get ahold of a fluke with a temp probe. I will try that too in the meantime.

What is the fix to increase the stack temp? Changing the primary air shutters didn't make much difference. Would reducing the excess air increase the stack temp? I'm wondering if there is a plate missing under the burners. There is one on the close half of the burners but not the back.

I appreciate your expertise with this. I don't get the feeling that this is an issue the techs see too much.

ChrisJ

Was the boiler at operating temperature when you took the measurements, or full of cold water?

Tim's the expert by far, but from what I recall when Joe S worked on my setup he wanted it steaming (operating temp) before he did anything. I would assume a hot water system should be at operating temp as well.

You're not going to get the same readings with 70F water in the boiler as you will if it's at 180F.

VDBLU

Water temp in the boiler was at about 130 degrees. That's measured at the top of the boiler. I'm not sure what the return water temp was but the boiler and pump had been running for 10-15 mins. The pump is set to come in at 120 and the high limit for the burner is set at 160. Even on the coldest days I've never seen it run above about 130.

SWEI

Combustion analysis requires measurements at light-off, during burn, and at shutdown in order to be truly useful.

VDBLU

Would a bypass help to increase the stack temperature? Still haven't been able to get the CO test. I might have to find a different contractor.

SuperTech

The CO test is a good indication if you have proper complete combustion. You want the CO as low as possible. If it's over 100 PPM you have a problem. The low water temperature and stack temperature indicates a problem. You have to check gas pressure to the burners with a good manometer. I would definitely seek out a technician with the proper diagnostic equipment.

Good luck with it. And please keep us posted on the outcome. I'm interested to see what happens with this.

VDBLU

I've been doing some research and found a 1931 "Handbook on heating buildings with Bryant gas boilers" at this web site: https://archive.org/details/SweetsCatalog1931Vol.D0012

Mine is a 1927 model 7-2 so it doesn't match any listed in the handbook. However it looks like the illustration of the Model 2. Some dimensions match, but my boiler is larger in most dimensions. I do have the remnants of the gas train described with the Robertshaw water temperature control and the thermostatic pilot. The point of all this is that the description of the gas pressure regulator states that it maintains a pressure of 1.5 oz. If I've converted that correctly that is 2.6" wc. We've already established that it was running at 3.5" wc and that is also what the new valve's factory setting is. The question is would reducing the gas pressure to the 2.6"wc help correct the low stack temp?

Also on the subject of stack temperature, page 3 of the handbook says under Staggered Gas Travel that "The hot gases from each burner are so baffled back and forth ... that only sufficient warmth is left in the gases to promote the necessary draft." Is it possible that the low stack temperature was by design? Or does this sound like marketing hyperbole?

While on the search, I found several references to Bryant guaranteeing 80% efficiency on these boilers. I've attached a screen shot of one ad that states: "...Bryant Tubular Gas Boilers are guaranteed to transmit 80% of the heat units from the fire to the water". What do you all think of that claim?

Finally, I had the technician out again with his CO meter. However it is a model designed for a "walk around" test. A Fieldpiece SCM4 I believe. So I'm back in the market for a tech with a combustion analyzer.

VDBLU

I've got another guy that is supposed to come by tomorrow. He seemed pretty enthusiastic about working on old boilers when I spoke to him. We'll see how that turns out. Anyone have any comments on the handbook info from the previous post?