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To tilt the dryer back, a 120 volt signal is applied to the front pistons solenoid connector #S5, and no voltage
is applied to the solenoid connector #S8. The internal spool in the valve will move and 80 PSI of air will enter
the bottom port of the front tilting pistons, extending the front tilting piston rods and tilting the dryer back for
loading. The top piston ports are bled to the atmosphere. To level the dryer after loading, the voltage signals
are reversed. No voltage is applied to the “S5” solenoid, and 120 volts are applied to the “S8” solenoid. The
valve spool will now move so that 80 PSI of air is applied at the top piston ports, while the bottom piston ports
are bled to the atmosphere. The piston rods will now retract, leveling the dryer. On a 2-way tilt dryer, the
rear tilting piston solenoid valve acts in the same manner.
The tilting piston valves are three (3) position valves. This means that, if no voltage is applied to both positions
(“S5” and “S8”) ALL five (5) valve ports are blocked. If the dryer is tilting or leveling and power to the dryer
is shut off, the pistons will lock in position, holding the dryer in a partially tilted position.
The dryer can be made to tilt faster or slower by adjusting the pistons 3/8-inch flow control valves which are
located on the pneumatic control panel.
4.
Internal and External Pilot Air Supply
On 2-way tilt dryers, a pneumatic safety circuit is incorporated to prevent both front and rear tilting pistons
from extending their rods at the same time. When 120 volts is supplied to the “S5” side of the front tilting
piston solenoid valve coil, the round internal spool in the core of the solenoid will move, allowing 80 PSI air to
flow into the bottom ports of the front tilting pistons, while the top ports of these pistons are bled to the
atmosphere. In addition to this 120 volt electrical signal, the spool also requires a 30 PSI supply of
compressed air to change its position. This pilot air can either be supplied internally, tapped off the 80 PSI air
supply connected to port no. 1 through holes in the body of the solenoid valve or it can be supplied externally
through the 1/8-inch F.P.T. connection located on either end of the solenoid valve. If no pilot air is supplied to
the solenoid valve then the spool cannot move, even with voltage supplied to the solenoid valve coil.
This can be used to prevent both sets of tilting pistons from extending their rods at the same time. When the
front tilting piston rods are extended, 80 PSI air is connected to the bottom piston ports, while the top piston
ports are bled to the atmosphere. So, by tapping the external pilot air supply to the rear tilting rods are
extended, then there is no pilot pressure available to the rear tilting piston solenoid valve so that its spool
cannot move and the rear tilting piston rods cannot extend if a 120 volt signal is sent to its “12” side solenoid
valve coil.
The external pilot air supply to the front tilting piston is tapped off the rear tilting piston top port air line so that
whenever the rear piston rods are extended, there is no pilot air supplied to the front tilting piston solenoid
valve and the front tilting piston rods cannot extend. On the solenoid valve supplied on the dryer, the #12 side
valve is externally piloted, while #14 side valve is internally piloted.
A valve can easily be checked for internal or external piloting by removing the two (2) screws which hold the
solenoid operator onto the valve. For an internal pilot air to be supplied to the valve spool. For an external
pilot, the solid sealing disc must be positioned on top of the internal port.
5. Loading Doors and Heat Reclaimer, Cool Down and Intake Air Damper
These solenoid valves are located in the 4-station manifold block on the pneumatic control panel. The front
load door piston, rear unload door piston (optional), and the sprinkler water valve are ALL controlled by their
own 3-way double acting solenoid valve.
The three (3) pistons that control the heat reclaimer damper, cool down damper, and intake air damper are
controlled by a single 3-way double acting solenoid valve.
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