2 stage

Paul S_3

Hey everyone. ...I just got a job to refit a terribly piped steam boiler. I guess by luck the original installer just slightly oversized the boiler just by 40 EDR. It is one pipe steam gravity wet return.i will be piping a 4 inch drop header... Boiler is a williamson gwa175... I personally like these boilers if installed correctly. Boiler is piped with (1) 2" supply....I will be improving the main venting, risers & radiators per steve's & gerry gills capacity chart as I always do....I will also be adding a vaporstat....I mentioned to the customer about the benefits of using a 2 stage gas valve and they approved that too....I have never used a 2 stage valve for steam, which valves do you guys use? How do you guys wire this setup? Any help greatly appreciated thank you Paul S

Jamie Hall

One way to do it is to use two vapourstats. High fire to start, then go to low fire at some handy pressure -- say half a pound or so -- with whatever cutoff seems to work. Have the high fire set to cut back in at perhaps 4 ounces... and low fire to cut back in at somewhere between that and the high fire cutoff.

But i've not tried it, so that may not work at all!

Paul S_3

Can I use just one like this? It looks it will work thanks Paul S

EBEBRATT-Ed

Can you post the M/N and mfg. of that valve??

Paul S_3

I don't have a model number that's why I am asking what valve does everyone use when they use a 2 stage gas valve on a steam boiler paul s

KC_Jones

I don't have all the experience in the world, but I put one on mine and it doesn't trigger. I have it set up to run on pressure from a vaporstat, the problem? I can't make any pressure to trip into low fire. Just one persons experience, but you could put in a provision for the control now and add it later if it is needed. If the boiler is matched well and you have good venting you might not make any meaningful pressure. I think I have made it to 1.5 ounces on a couple longer runs, but that's it. Just throwing it out there.

EzzyT

Ive been using the Robertshaw 700-053 2 stage gas valve it works great and I use 2 vaporstats to trigger the high and low fire

lchmb

I wonder (for those that dont create enough pressure) if you could use an aquastat on the return. Once it see's a certain temperature it kicks the system to low fire..

JStar

Robertshaw 700-053 for up to 300K and 700-062 for up to 700K. Wire everything exactly as normal, but split the MV control leg going to the GCV into two wires. One goes to the GCV, and the other goes through the Vaporstat and low-fire solenoid valve. You can get away with using the factory pressuretrol as the main cut-off.

Abracadabra

I use honeywell v4944 with a vaporstat to control hi/lo fire. Original pressuretrolls are left on boiler as safeties.

vaporvac

Could a two-stage Tstat be used on systems that don't build enough pressure to trip the Vstats?

Abracadabra

vaporvac said:

Could a two-stage Tstat be used on systems that don't build enough pressure to trip the Vstats?

Don't think so. If you don't build enough pressure to trip a vaporstat you could setup a magnehelic like @ChrisJ or use an aquastat on a return line.

ChrisJ

Abracadabra said:

vaporvac said:

Could a two-stage Tstat be used on systems that don't build enough pressure to trip the Vstats?

Don't think so. If you don't build enough pressure to trip a vaporstat you could setup a magnehelic like @ChrisJ or use an aquastat on a return line.

I think you may be thinking of my Photohelic idea.
The Magnehelic I'm using just shows pressure. The Photohelic is a magnehlic based pressure switch. By no means cheap, but by all means awesome.

They go as low as 0-0.5" w.c. and since they are a differential setup, I see no reason why you can't use one to measure vacuum as well.

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gage-Switches-Dial/Series3000MR-3000MRS


I've never used one but it sure got my attention when I came across it.

Abracadabra

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Switches/Series1900

ChrisJ

Abracadabra said:

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Switches/Series1900

Ah,
I have a 1823-2 on my system set to trip @ 1 ounce.

But, they are just boring switches, not nearly as cool as a Photohelic.

JUGHNE

Forced air furnaces that I see that are 2 stage, the initial ignition is at high fire and after 30 seconds or so it will drop to low fire.
I'm assuming the first start at high fire is to establish draft by warming the HEX & flue. (Even though there is a draft inducer fan using PVC venting.)

Could steam boilers light off correctly and establish enough initial draft if they only cold start on low fire?

ChrisJ

JUGHNE said:

Forced air furnaces that I see that are 2 stage, the initial ignition is at high fire and after 30 seconds or so it will drop to low fire.
I'm assuming the first start at high fire is to establish draft by warming the HEX & flue. (Even though there is a draft inducer fan using PVC venting.)

Could steam boilers light off correctly and establish enough initial draft if they only cold start on low fire?

That depends on a bunch of different things, no?
My 30 foot 6" B vent seems to draft real well even when it's warm outside. I assume an oversized masonry chimney on the outside of a home would be a nightmare.

JUGHNE

The reason for inquiring is that some gas trains (mostly larger) incorporate an additional low gas pressure safety switch to lock out ignition because some burners may have partial or delayed ignition a result.