THERMOSTAT GAS GOVERNOR
The supply of gas at the burners is controlled by the expansion and contraction of rods immersed in the molten metal in the crucible at the left-hand side of the metal pot. These rods are of a special alloy, which is extremely sensitive to variations of heat. No mercury is used, so that the governor is not affected by the pressure of the gas at any time.
The principle upon which the thermostat is built, is the difference in expansion of two metals under heat.
The part of the thermostat which is immersed in the metal is made of cast iron and has a hole or pocket in which the rod of composition metal sets. The upper end pushes against a hinged lever; the other end of this lever operates a valve plunger. The expansion of the thermostat rod being greater than cast iron, raises the valve lever, which forces down the valve plunger, seating the plunger nearer the valve seat. This cuts down the flow of gas to the burners. The rod contracts as the metal cools, and allows the valve spring to open the valve.
Underneath the valve rod cap and encircling the valve rod, is a spiral spring which raises the valve rod as the expansion rod contracts, which opens the gas inlet, and also keeps the expansion rod pushed to the bottom of the pocket.
In the lower end of the valve is a hole to prevent the burner going out if valve is entirely closed. This hole must not be enlarged.
The valve adjusting screw is slotted and has a setscrew inserted through the valve lever to keep the adjusting screw from turning. Between the head of the adjusting screw and under part of the lever is a spring which forces the head of adjusting screw against the cap of the valve. When tightening up on the adjusting nut the spring closes, releasing some of the pressure on the valve, permitting more gas to pass the valve. By loosening the adjusting nut the spring expands, forcing the valve down, cutting down the flow of gas to the burners.
To adjust thermostat, if metal is not hot enough, raise the adjusting screw by turning the adjusting nut farther down; if the metal is too hot, unscrew adjusting nut, allowing the adjusting screw to force the valve farther down.
The screw in the top of the expansion rod is for the purpose of making the rod longer, should occasion require. Do not change this screw unless necessary.
There are two sets of rods and valves on the regular equipment. One set regulates the gas to the pot burners and the other regulates the gas to the mouthpiece burner. Experience has shown that it is impractical to regulate the mouthpiece from the crucible, so cut off this part of the regulation and use a gas burner cock.