290 APPENDIX VII
practically impossible to secure the necessary clearances to
install different equipment or to provide the necessary rearrange-
ment of the flues. This obstacle is somewhat difficult to over-
come. The first installation is always difficult to secure, and in
many cases it is the only one made.
A certain amount of producer gas will be lost every time the
furnace is reversed. The gas regenerator and certain other parts
of the furnace are full of gas prior to reversal. A portion of this
trapped gas passes into the furnace and burns, but part of it will
be drawn backward into the chimney ^flue. This loss cannot be
eliminated. The more frequently the furnace is reversed, the
greater the loss.
Wind exposure has a certain effect upon furnace operation. It
affects the chimney draft appreciably. At the same time, it will
have an effect upon the velocity with which the air enters the
reversing valve, according to^its exposure. Mr. Allyn Reynolds
stated, at the 1913 meeting of the British Iron and Steel Institute,
that a wind blowing at the rate of 20 miles an hour caused a
variation in the rate of flow of air into the reversing valve of
70 to 350 ft per minute. The entry rate desired was 180 ft per
minute. As variations of this kind are sudden and extremely
irregular, it is difficult to compensate for them.
The use of a fan for introducing the air will not eliminate such
variations entirely; the fan merely causes a motion of the air
within itself, taking the air from the low-pressure side and deliver-
ing it to the high-pressure side. Any increase in the suction pres-
sure will increase the delivery rate of the fan. A great advantage
of a fan, in delivering the air, lies in the fact that it renders the
furnace independent of the stack effect of the regenerators and
uptakes in impressing the air velocity at the port, bringing this
variable more thoroughly under control. If stove-type regenera-
tors extending above the platform are used, a fan will be neces-
sary to force the air through them.
Considerable heat is dissipated from the wall and roof surface
of the regenerator chambers, the amount depending upon their
exposed surface and the air or wind currents to which they are
exposed. The proposal to insulate this surface has been actively
considered. The problem is similar to that of the insulation of the
hot-blast stove, except for the fact that the regenerator usually
works at much higher temperatures than the hot-blast stove.