American Dryer Corp. AD-400 - Manual (Page 36)

The tilting piston valves are three(3)-position valves. This means that, if no voltage is applied to both
positions "12" and "14" all five valve ports are blocked. This means that, if the dryer is tilting or leveling
and power to the dryer is shut off, the pistoirs 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 tilting pistons 3/8" flow control valves
which are located on the pneumatic control panel.
3. Intemal/Extemal Pilot Air Supply
On two-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 115 volts is supplied to the "12" 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 115-volt electrical signal, the
Sfxx>l 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 FPT 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 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
piston solenoid valve off the air line to the front tilting piston top port, whenever the front tilting piston
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 even if a 115-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 the '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, the "o" ring should be positioned over the
internal pilot supply port. This allows 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.
4. Loading Doors, Heat Reclaimer Damper, Solenoid Valves
These solenoid valves are located in the 7-station manifold block on the pneumatic control panel. Each
door piston and the heat reclaimer piston is controlled by two (2) of the 3-port/2-position cartridge
solenoid valves in this manifold block.
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