What is tube connection between gas valve and combustion chamber

keihancpu

Hello all
i have a question about gas valve. in some wall boilers there is a tube connection between gas valve(Ex: Sit 845) and combustion chamber. Exactly what is it doing ?
Thank you

Tim McElwain

It is from the regulator on the gas valve. The regulator has to be in the same environment as far as air. So a normal gas valve does not need the tube on atmospheric type equipment. It gets its air for combustion from within the same room as the regulator therefore no tube needed. However on systems which get their air for combustion from outdoors then the vent on the regulator has to be in the same environment so it is run into the combustion chamber.

Tim McElwain

On some older systems however (pre 1959) there was a small tube that ran from the gas valve to the pilot. It was called an External Bleed Type Diaphragm Gas Valve. On a call for heat a pressure port in the valve would be closed and a bleed port would be opened then the gas would bleed off the top of the diaphragm and that caused the pressure under the diaphragm to be greater than above so the valve would open and gas would flow. Once the gas bled of the top of the diaphragm it would stop.

When the call for heat ended the pressure port inside the valve would open and the bleed port would close and pressure would build back up on the top of the diaphragm. When it equaled the pressure under the diaphragm then the spring and gravity would close the valve seat stopping all flow of gas.

A typical service call on this type of valve would be the valve would not open when powered. What was typically wrong was the bleed tube from the valve got plugged. All you have to do is clean the tube.