90% furnaces

drhvac

usually have a hose going from the burner box then teed, one side going to the pressure switch, then the other one going in to the manifold side of the gas valve. Could anyone tell me what exactly this hose is doing? I know it has something to do with gas valve regulator, but I don't understand it. It is a low pressure, much lower than the lowest pressure the gas valve is sending to the manifold. Thanks

unclejohn

Tim Will Know

But my guess is it's just a vent line and not sensing pressure. Carrier is using the same valve on there 80% & 90% single stage and the instructions say on the 80% that the tapping for the hose does not need to be sealed.

JStar

Hose

I've always been told that it equalizes the pressure between the gas valve and the sealed combustion box. In an 80% furnace, there is no sealed combustion box, so the gas valve and burners are naturally equalized.

Ironman

That's It

Joe's got it. The gas regulator is maintaining pressure relative to the atmospheric pressure at the burner. Since the burner is in a slightly negative atmosphere from the induced draft, the regulator needs to "sense" pressure at that point.

Tim McElwain

Very good "grasshoppers" Regulators on appliances

always have to have the vent (small hole in the regulator) no gas coming out at the same atmospheric pressure as the burners them selves. Soon atmospheric burners (air from with in the room) the vent is open (may have a vent limiter).



On sealed chambers you will almost always find a hose going from the built in regulator on the gas valve to the combustion chamber so they are at the same atmospheric pressure. The vent in theory is so the regulator can "breathe".

drhvac

regulator

to help me understand this better, maybe by answering this question would help me. What would happen if that hose wasn't there? I'm assuming it would affect the manifold pressure a little?

SWEI

It would make

the gas flow match the ambient air pressure instead of the CAZ pressure.