DESIGN OF OPEN-IIEARTII FURNACES
to the cool gas or air passing to the regenerators, it soon warps
and becomes leaky. These leaks permit air to pass directly to the
stack and cool down the waste gases; or, if the valve is used for
gas, there is continual leakage of gas, which burns either in the
valve or in the stack flue.
While many reversing valves are water-scaled, most of them,
like the butterfly valve, during the* operation of the valve, open a
direct connection, practically the full area of the valve from gas
main or air to the stack. Then* have been a few valves which cut
the furnace, gas and air entirely off from one another and the
stack, but these valves have not come into extended use.
Water-sealed valves are used extensively. As long as the seal
FH»S. 15H arul 159, -Pyrometer Diagrams of Stack Temperature's, Abnormal
conditions shown by suddctn upward kick in Fig. 159 jiro probably dun
to nir ioukiiKft mid the combustion of chcjokdr ^RHC^H passing along the
fhio to the* Black,
holds they are tight, but there are usually structural limitations
to the? depth of the seal When exposed to gas pressure; on one
side and to the stack depression on the other, the seal is unbalanced
and may readily be* broken by surges or explosions. In Home eases,
a considerable! water area is exposed to the entering gas or air,
as well as to the waste gases.
The producer gas and the stack gases are several hundred
degrees hotter than boiling water and will absorb a considerable
amount of moisture from a very small area of water surface.
Other valves expose very little water surface. With nil of those*
vulvas the sealing lip must bo raised to clear the water surface
and the port rims, whenever the valve in operated. From the