losing preasure (fast) and vaporstat

John Barba1

Good morning.

well this electrical guy got a good education from Tim Mc Elwain last week on the burner derate thing and all is back up to the proper firing rate for the boiler.

according to the EDR rating on my smith gb 200 I should be right on what I need. my boiler at max input is rated 421 sq ft , my radiation load is 331 including piping. at 20% de rate I should be at 336 square ft or there abouts. I should be right on but the system is acting way overfired in some ways.

My flame is set at 131,000 btu , nice and blue with a 335 deg stack temp.

Ive noticed my system does heat faster now but not without a few issues.

1) When Im maintaining temp and had a presurtrol set for 2 psi/.5 psi I would build preasure then short cycle,once or twice before the stat was satisfied. when at preasure my off time was about 90 sec my on time was 4-6 mins.

2) during a recovery where im going from say 62 - 67 degree the system gets up to preasure and will repeat the on on off cycle many many many more times before the T stat opens.

last night I installed a vaporstat (0-16 Oz) and set the preasure at 9 oz and the diff just below 9 oz (0 oz) .

Things heat up real nice at 9oz but the my cycle time when at preasure is worse than when using the preasuretrol.

Now I realise that Im working in OZ vs LB.

with the vaporstat my off time is only 40 seconds somtimes less and my on time is only 2-3 mins max (once im at preasure) so this puts me at doing lots (many many many) little cycles before the stat is happy.

Im real curious about the rate I lose preasure, Isnt 40 seconds a bit too fast from 9oz? it was 90secs from 2psi.

with a bit longer cooling time or at a lower fireing rate My run time gos up quite a bit.

I shut my power off for 2 mins when it reached 9oz and when I was back on I ran for 17 mins before I reached 9oz again then the stat was made before machine gun short cycle started again. all units Rads and baseboards were hot.


I think the preasure drop is my downstairs! I have a split system One pipe rads Up 2 pipe baseboard down.

my 1st floor is 38 ft of baseray cast baseboards that are set up Burnham style ,2 pipe with a wet return and vented without traps .

2 of the baseboards actually have 12'+ of pipe that runs in the air before it drops to the wet return near the floor. I was thinking these could be the culprits.

also the end of the steam main drips into the wet return and does not have a drip trap.

this losing preasure so fast is driving me crazy cuz it just causes too much cycling .

Note: there are no leaks I dont add water but once or twice all winter.



in final what are your thoughts??? are these cycle times somwhat normal? any thoughts on correction.

I am thinking of adding a 2-3 min +- off delay timer (I do controls for a living) to the vaporstat circuit to allow things to cool/dwell a bit before it lights off again which will give me a longer run time and perhaps let the latent heat work a bit before I turn the flame back on??.,

does this sound feasible??

many thanks, this is a great site and Like I told Tim McElwain a great group of gents.

Have a great day "John"

Steamhead

Try

setting the Main at 12 ounces and the Differential at 7 ounces. This should give you a bit longer cycle without building too much pressure.

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gerry gill

i dont know if this helps, but

we put the vaporstat at the end of the main, off a pigtail..not on the boiler..this makes for longer run times..we regularly see twice the pressure in the boiler than at the end of the main, albeit still ounces..that stack temp seems low to me..whats your chimney draft reading? just curious..