Fig. 10. Air Unloading of Intake Valves--3/4
The unloader pilot is located on the crankcase and is
connected to the unloader by a copper line. The l/2-
and 3/4-hp (0.37 and 0.56 kW) units use a pilot that is
mechanically activated (see Fig. 11). All other units are
operated by oil pressure (see Fig. 12). Disassemble and
clean units if suspect. See PARTS LIST section for
repair kit numbers.
Fig. 11. Three-Way Valve Assembly-l/2- and 3/4-HP
(0.37 and 0.56 kW) Units.
- H E A D
Fig. 12. Hydraulic Unloader Assembly-l-IHP (0.75 kW)
P R E S S U R E R E G U L A T I N G V A L V E
The l/3- to 2-hp (0.25 to 1.5 kW) units use a Honey-
well PP901 or PP902 PRV. For detailed maintenance
and repair information, see Form No. 75-2558.
The prv station used on the 3-11~ (2.2 kW) units is a
combination of a Pall-Trinity-Micro Corp. filter, and a
Norgren regulator and relief valve (see Fig. 15 and
To perform maintenance and repair work on the prv
station, shut off air supply
system by manually operating the drain (push red button
on drain valve).
All valves and dampers return to the normal posi-
tion when system is bled. Study job drawings for
critical problems before bleeding down system.
The regulator and relief valve can now be replaced or
repaired with the appropriate repair kit (see PARTS
After repairing or replacing, slowly turn air back on,
checking for leaks.
Units and Larger.
tank. Bleed down the