31
Plumbing of the constant speed unloader valve is
covered in Section 1, Compressor Installation.
Three air pressure ranges are available for constant
speed unloading. The pressure at which the
compressor loads and unloads must fall within one of
the following three ranges in order to use a constant
speed unloader valve:
RV006
Unload pressure of 30-70 psig.
Uses a red spring.
RV007
Unload pressure of 71-150 psig.
Uses a yellow spring.
RV008
Unload pressure of 151-250 psig.
Uses a green spring.
The constant speed unloader can be adjusted
throughout each different pressure range, giving a
load/unload pressure and differential pressure range
according to Table 6.
The constant speed unloader has three adjustments,
allowing setting of: start/stop vs. continuous run
control; unload pressure setpoint; and unload pressure
differential (Figure 20).
To set the unload pressure, turn the screw marked
“unload pressure adjustment” clockwise for increased
Unloader Part
Unload
Min. Differential
Max Differential
Number (PSI)
(PSI) (PSI)
RV006 30
2
4
“ 40
5
8
“ 50
5
8
“ 60
5
8
“ 70
5
10
RV007 80
5 10
“ 90
5
12
“ 100
5
13
“ 110
5
15
“ 120
5
15
“ 130
5
18
“ 140
5
18
“ 150
5
20
RV008 160
5
15
“ 170
5
20
“ 175
5
23
“ 200
5
25
“ 250
10
30
Table 6: Constant Speed Unloader Valve Differential Pressure Setting
unload pressure, counterclockwise for decreased
unload pressure. When adjusted properly, tighten
down locknut.
The differential pressure is set by use of the screw
marked “differential adjustment”. Increase the
differential pressure by turning clockwise, decrease by
turning counterclockwise (Figure 20). When adjusted
properly, tighten down the locknut.
The constant speed controller has an option allowing
the user to lock down the regulating ball, closing off
passage of air to the unloader towers. When manually
shutoff via this option, the constant speed unloader
will not actuate the unloader towers. This allows a
motor start/stop control. This option is controlled via
the knurled knob marked “manual shut-off” in Figure.
Turn the knob clockwise until it stops to turn off constant
speed unloader control. Back the knob out all the way
counterclockwise to allow constant speed unloader
control. In either case, the hydraulic unloader will still
be operative.
ADJUSTMENT OF AUTOMATIC
UNLOADER CONTROLS
Some compressors have purely automatic unloader
devices, which are controlled by a pressure switch
(usually located in the control panel). These
compressors accomplish unloading via the two methods