NITROGEN OUTLET
VENT
NITROGEN OUTLET
PILOT VENT
UPPER PILOT VENT
CHAMBER "A"
SPOOL
CONTROL
VALVE
SUPPLY
SUPPLY
DRIVE
NITROGEN
NITROGEN
SIDE OF
PRESSURE
PISTON
OUTPUT
SIDE OF
PISTON
INLET
CHAMBER "B"
CHECK
NITROGEN OUT
LOWER PILOT VALVE
VALVE
OUTLET CHECK VALVE
PISTON MOVING DOWN
AT TOP OF STROKE
With control valve in DRIVE position, supply nitrogen pressure
With piston in upper position, upper pilot valve is open. This
acts on upper side of piston. This forces piston assembly
exhausts chamber B. Supply nitrogen pressure in chamber A
downward and delivers nitrogen under high pressure thru the
then moves control valve to DRIVE position.
outlet check valve. Nitrogen from lower side of piston is
exhausted thru control valve spool.
NITROGEN OUTLET
VENT
NITROGEN OUTLET
VENT
NITROGEN
NITROGEN
GAS
GAS
NITROGEN
IN
AT BOTTOM OF STROKE
PISTON MOVING UP
As piston reaches bottom position it opens lower pilot valve.
With control valve in RETURN position, supply nitrogen
This delivers pressure to chamber B. Since chamber B has
pressure acts on lower side of piston and moves it upward.
larger area than chamber A, control valve is moved to RETURN
This pushes the piston assembly up, sucking gas in thru inlet
position
check valve. Nitrogen from upper side of piston is exhausted
ASf0907
thru control valve spool.
Figure 9-7.--Flow during a motor and pump assembly cycle.
pilot control valves. The cycling control valve operates
line. The motor and pump assembly has an output
pressure 30 times the drive pressure. It is an automatic
without springs or detents, and is cycled by alternately
cycling device, cycled by a nondetented, unbalanced
pressurizing and venting (by action of the pilot valve)
spool that is alternately pressurized and vented by the
chambers of an unbalanced pressure-operated spool.
pilot system. The assembly is designed to operate dry
In figure 9-7, the gas flow is illustrated for one cycle of
(without lubrication) to supply nitrogen that is free of
the motor and pump operation. In figure 9-7, notice the
hydrocarbon contamination.
drastic difference (30:1) between the drive side and the
The pneumatic drive section consists of a drive
output side of the piston.
piston assembly, a cycling control valve, two pilot
The parts breakdown shown in figure 9-8 also
control valves (mounted in the upper and lower caps), a
illustrates the relative sizes of the input piston and the
flow tube to direct flow to the top side of the drive
output piston.
piston, and a pilot tube to connect the upper and lower
9-10
