Working out issues with Dunkirk PSB-7D replacing old boiler

Landy

Problems:

1. The boiler still has more water level change/bouncing during steaming than I think should be there, even after very extensive skimming. Also, at some points during the heating cycle (mostly early in the cycle) some water runs down the inside of the site glass.



2. It takes a long time for the steam to get to the end of the 2 mains. It was 16 minutes, but with vents added it is down to 8 minutes.



I have recorded a 10 minute video tour of the system on YouTube which can be viewed at <a href="http://www.youtube.com/watch?v=wNlzfB3zS_A">http://www.youtube.com/watch?v=wNlzfB3zS_A</a> for your viewing pleasure. There are also a couple more videos posted on the same GradientLens channel showing some of the early problems that have been fixed by thoroughly skimming the boiler (took care of most of the surging) and replacing a defective Vaporstat that let the boiler run at too high a pressure (took care of water pouring out of main vent).



Background: In January 2013, we replaced a 24 year old boiler that caused a house fire with a Dunkirk PSB-7D. The 24 year old boiler replaced the original boiler put in about 1925, so the pipes, radiators, etc. are OLD. We were not clever enough to have recorded the waterline on either of the old boilers, but I think this one was set about 6-8" lower than the last. The two mains are 2 1/2" pipe, north 60' long and south 70' long. The EDR load on the north main is 290 sq.ft. and on the south 436 sq.ft. for a total load of 174275 BTUH on the boiler if all radiators were fully open. We are running the boiler with a high pressure of 13 oz/in^2 and a differential of 6 oz/in^2.



What I am left with now is trying to decide if I really need to replace the Bullhead T that feeds the two mains as this will be very expensive and figuring out how to get steam to the end of the mains quicker. I will discuss the second part of this first as that is something I definitely want to address before the end of this heating season. The Bullhead T is something I will ponder over the summer, but would love to hear your opinions about. I know it is wrong, but is it really a significant problem for me?



I have measured time for the steam to get to the end of the mains, starting from the time the boiler starts making steam with a pressure of 4 oz/in^2 on the pressure gage. I then walk to the end of the mains and hold my hand there waiting for them to get hot. Originally, this took about 16 minutes. We have installed a Hoffman 75H air vent at the end of the mains and this drops the time to 8 minutes. My questions here are what should I expect for the time? Do I need more vents at the end of the mains? Is the 75H that was installed OK or should it be just the Hoffman 75? My boiler contractor says the 75H is just a more rugged version and works just as well for low pressure systems. Is he correct? Any other ideas how to get the steam to the ends of the main quicker or problems other than venting that I should be looking at?

nicholas bonham-carter

Hoffman 75h

Try taking the main vent off completely, and then time the steam to its arrival at that location.

You want enough main venting on the mains so that the resistance is as low as an open hole, verified by a low-pressure gauge at one ounce back-pressure.--NBC

Landy

added another 75H

I added a second Hoffman 75H vent to the South steam main and the time to get steam dropped to 4 minutes.



Main Vent ==> Time

no vent ==> 16 minutes

1 vent ==> 8 minutes

2 vents ==> 4 minutes



I wonder what adding a 3rd would do? Nicholas, I didn't just leave the pipe open as I didn't want to deal the live steam, but I may just for grins add a valve that I can open as a test during venting and then close once I start getting much steam.

nicholas bonham-carter

Open pipe test

I imagined you could turn off the boiler as soon as steam flows out of the tapping.--NBC