When one furnace is thinner, the other is designed to swell. The valve in the chamber with the first inflated air chamber is open while the valve in the second chamber is closed. Then gas enters the first chamber. When the gas lamp is turned on, it absorbs gas from the furnace of the first chamber, and the gas in the chamber pushes the furnace. The furnace then swells, the second chamber swells, and the first gas is pumped into the chamber. Then the valve in the first chamber closes, and the valve in the second chamber opens, and gas is introduced. Due to the pressure of the gas, the gas in the furnace enters the lamp, causing the furnace to swell and the furnace to inflate again.