1. 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 application 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 /in2), depending on the net retention of preservative desired and the resistance of the wood.
2. After the period of preliminary air pressure, preservative 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 preservative, or until enough has been absorbed to leave the
required retention of preservative in the wood after the
treatment.
3. At the end of the pressure period, the preservative is
drained from the cylinder, and surplus preservative
is removed from the wood with a final vacuum. The