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236                                  APPENDIX VII

5.  Gas-stack valve B is opened.    (This passes the gas

trapped in the gas checker K to the flues and boiler,
thence to the stack);

6.  Gas-stack valve G is closed;

7.  Air-inlet valve E is opened.    (This admits air to the


8.  Gas-inlet valve H is opened;

9.  Air-stack valve D is opened;

10. Steam is turned on to the producers.

The important feature of this system of valve operation is the
time interval between the opening of the gas and the air stack
valves on the same side of the furnace. This interval must be
sufficient to permit the inflammable gases in the gas checker to
pass into the flues and to the stack before the air-stack valve is
opened. In the plant where this system was introduced the
number of explosions was reduced from about 40 per day to 4 in
411 reversals in a period of five clays.

Several other systems are in use, and in some installations
the valves are. interconnected in sets which are operated simul-
taneously. Different arrangements of flues and different valves
will require some modification of this system, the essential point
being the interval between the opening of the gas-stack valve and
the air-stack valve.

This sequence of valve operation will not eliminate explosions
unless the valves and the flues are sufficiently tight to prevent
any air entering the system while the gas trapped or pocketed in
the checker chamber is passing to the stack.

Probably the most important portion of the waste-heat boiler
installation is the arrangement of the boiler setting with regard
to the manner in which the gases pass through it—that is, the
baffling and the location of the gas inlet and outlet. The design
of boiler settings and their baffling has been the subject of much
experimenting, but unfortunately most of these experiments have
been made without any very clear conception of the action of the
hot gases while flowing past cool metallic surfaces.
The ruling temperature in steam boilers is very low.   For this