The coating thus consists of two layers of asphalt and two of
saw-dust. When the pipe leaves the finishing rolls, the coat is hard and
smooth and about 1 3/16 in. thick. This describes the coating as done at
Bay City, Mich.
At Elmira, N.Y., one application of asphalt and saw-dust only, without a
finishing dry roll, completed the work; but the band was run through a
bath of hot asphalt as it was wound, thus coating its underside also.
This initial treatment of the band on the Wykoff pipe is necessary
because the exterior of the stave is neither planed nor turned to a
circle. The exterior of the pipe forms a polygon, and the band is in
perfect contact only at the angles. The theory in regard to the Michigan
pipe is that the perfect contact of the band and the wood on the true
exterior circle excludes air from the under surface of the metal, and
prevents corrosion. Experience appears to justify this theory.
_Cast-iron Pipe_.--Beginning at the first pumping plant at Coyote, at
Mile 156, and running up to Mile 166, and again commencing at the Luna
pumps, at Mile 171, and extending up to Mile 179, the minimum pressure
on those portions of the pump main is more than the 130 lb. per sq. in.
allowed for wood pipe, and the final estimated maximum pressures run up
to 310 lb.
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