- Air under pressure is forced into the treating cylinder,
which contains the charge of wood. The air penetrates
some species easily, requiring but a few minutes appli-
cation of pressure. In treating the more resistant species,
common practice is to maintain air pressure from
1/2 to 1 h before admitting the preservative, but the
necessity for lengthy air-pressure periods does not seem
fully established. The air pressures employed generally
range from 172 to 689 kPa (25 to 100 lb in–2), depend-
ing on the net retention of preservative desired and the
resistance of the wood.
2. After the period of preliminary air pressure, preserva-
tive is forced into the cylinder. As the preservative is
pumped in, the air escapes from the treating cylinder
into an equalizing or Rueping tank, at a rate that keeps
the pressure constant within the cylinder. When the
treating cylinder is filled with preservative, the treating
pressure is increased above that of the initial air and is
maintained until the wood will absorb no more preser-
vative, or until enough has been absorbed to leave the
required retention of preservative in the wood after the
treatment.
Chapter 15 Wood Preservation
Figure 15–5. Typical steps in pressure treating process: A, untreat-
ed wood is placed in cylinder; B, a vacuum is applied to pull air out
of the wood; C, the wood is immersed in solution while still under
vacuum; D, pressure is applied to force the preservative into the
wood; E, preservative is pumped out, and a final vacuum is pulled
to remove excess preservative; F, excess preservative is pumped
away, and the wood is removed from the cylinder.