[Al Skierkiewicz]

Might be more like:

R78
If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be
used in accordance with this section, as illustrated in Figure 4-15.
A. Compressor
B. Pressure Relief Valve, calibrated for release at 125 psi.
C. Pressure Switch, Nason #SM-2B-115R/443 or identical specification (115-120 psi), non-adjustable, equivalent.
D. Pressure Vent Plug
E. “Stored” Pressure Gauge (upstream from Primary Regulator)
F. “Working” Pressure Gauge (downstream from Primary Regulator)
G. “Working” Pressure Regulator

For everyone, the part number shown above is the device sold by AndyMark and the part number refers to a set point of 115 psi. The data sheet specifies the set point at +/- 1 psi with a differential (hysteresis) of 8-16%. That translates to turn compressor back on when the pressure falls below 97-107 psi.
While it is hard to see due to the formatting of the pdf, remember...
R81
“Stored” air pressure on the ROBOT must be no greater than 120 psi.