The PCS VacDry system is the result of
more than 20 years of research and
development.
This vacuum kiln was designed by Vincenzo Pagnozzi
in 1970. The Italians knew the basic design as early
as 1970, but the
T basic design did not dry wood as
imagined.
Flexible tops require full chambers with no irregularity in
thickness and no large gaps to prevent damage to the plates.
A short lesson in physics may be in order. With the beaker on the left,
water molecules with sufficient energy can bounce free from the surface.
But, with sufficient heat, water molecules will move with sufficient force to
break bonds within the liquid. The collective force is called vapor pressure.
When vapor pressure is as high as ambient pressure, water boils.
Heat transfer in a vacuum is
difficult
due to:
•not enough air for convection
•not enough contact for
conduction
•not high enough temperature for
radiation
Because evaporation uses heat,
heat
must be continuously replaced
and
early vacuum kilns couldn't
effectively replace that heat. in
Modern data acquisition systems now enable us to collect information 24/7 and
to display that information graphically. This shows the relationships of
parameters which need to be controlled. The graph above is the start-up of a
new kiln charge..Chamber pressure is shown in green. Wood temperature is
shown in olive and blue shows behavior of the humidity.
Chamber pressure cycling shown in red and humidity in
blue.
The short peaks in the bottom of the pressure cycle are the result of the control
system interrupting the vacuum pump to empty the condensate collection tank.
They indicate drying rate. When chamber pressure was increased, drying
slowed until the water in the wood reached the new boiling point.
Chamber pressure cycling shown in red and humidity in
blue.
This process can be shown in reverse. When chamber pressure is
reduced, water boils out rapidly until the wood cools and vapor
pressure is reduced.
Chamber pressure cycling shown in red and humidity in
blue.
Humidity must be controlled when drying heavy red oak, all white oak or other
difficult thickness or species. In this graph, the humidity was dangerously low
until the control system sprayed it up to a safe level.
Chamber pressure cycling shown in red and humidity in
blue.
The brief shots of spray make the blue spikes on the left side of this
chart. As water leaves the wood at an increasing rate, the required
spray diminishes until none is needed.
12/4 Red Oak flitch,
flat sawn right
through the pith.
6 +/- 1% in 12 days, fresh off
the saw with absolute
minimal checking in even the
hardest to dry areas.
And the process leaves the wood incredibly stress free with no need for conditioning.
Stress free
A holly flitch: big and
valuable, but hard to
dry. And the VacDry
kiln can be adjusted
to do it.
Dried in a VacDry kiln (top)
and Air dried (samples cut
from the same board).
Figured red beech from New Zealand is a Nothofagus and one of the most difficult
to dry species in the world. And the VacDry kiln can be adjusted to do it.
The heating water temperature is shown in red and the calculated
moisture content is shown in blue.
All North American hardwoods and softwoods are dried with similar
schedules. The heating water ramp rate is adjusted to accomplish a
drying rate that is set by the characteristics of the wood.
One of the VacDry research systems installed at our Jersey Shore
facility. This chamber will hold 2500 board feet of 8/4. The small, red
boiler on the right supplies two kilns and heats the building.
The whole process is monitored and controlled automatically. We monitor
and assist new customers anywhere in the world.
We operate an R&D kiln in Napier, New Zealand from our offices in Jersey
Shore, PA.
A liquid-ring vacuum pump will run quietly and efficiently for years. All
components are chosen to provide years of trouble free service.
The system collects
every drop of
condensation.
There is no harmful
discharge of volatile
organic compounds into
the atmosphere.
The water from some
species may actually
offer valuable byproducts.
The heating system is a
closed loop, providing
precise temperature
control for precise vapor
pressure control.
A sophisticated material handling
system can be added.
This system uses a 'vac grab'
moved with a bridge crane that is
driven with a joystick.
Heating plates can be
moved with a vacuum
grab.
Vacuum is created inside
the suction cups by
blowing shop air across
venturis.
Now layers of lumber can be lifted on or off the kiln cart. One man can load or unload
a kiln charge but we recommend a second person as a “spotter”.
Our biggest
chamber holds more
than 10,000 board
feet.
Two chambers can be bolted end-to-end to dry timbers up to 52 feet
long.
Baseball bat billets being
dried at an Amish sawmill.
A VacDry 4 stuffed with hard
maple in Canada.
Adjustments to the control
system can enable the system
to
dry the most incredibly difficult
wood. This Amboyna burl is an
example.
The burl was
dried
in one of our R&D
kilns. The burl
cost $8000 at the
time of purchase
in SE Asia and we
gently dried it for
24 days.
The customer
had hoped to
get enough
material for this
$25,000 rocking
chair.
Instead he got two! Find out what PCS VacDry can do for you,
today.