Principles of Operation (Cont)
1-55. PRESSURE GOVERNOR (CONT).
Whenever the transducer signal is below 0.3 VDC or above 4.8 VDC, a sensor
fault will be logged and SENSOR will be displayed in the message center.
SENSOR will flash if the failure occurs while the pressure governor is
operating in psi mode. Once a failure is detected, the pressure governor can
no longer maintain a pressure setting. It will hold the current water pump
engine RPM and only operate as a throttle. Once SENSOR is displayed in the
message center, SENSOR will not clear until power to the pressure governor
is reset. It is extremely important that the cause for this message is
investigated. The pressure governor cannot discharge pressure properly
unless the SENSOR signal is reliable and correct.
If the INC switch is held, the pressure governor will not allow a change
greater than 80 psi (552 kPa) without releasing the INC switch and pressing
it again. This is only applicable when the discharge pressure is above 90 psi
If the discharge pressure drops below 30 psi (207 kPa) for any reason, the
water pump engine speed will not be increased. The pressure governor
output voltage will reduce to the last known value where the pressure
setpoint was obtained. The message center will display INTAKE during this
low pressure condition. If the pressure increases above 30 psi (207 kPa),
OPERATOR will flash in the message center and the pressure governor will
not increase output unless the operator presses the INC or PRESET switches.
If pressure above 30 psi (207 kPa) is not regained in 5 seconds, the pressure
governor will return the water pump engine to idle and display LOSUPPLY.
The operator must make certain that the water supply is adequate and then
reinstate the pressure governor using the MODE, INC, and/or PRESET
The pressure governor has a trim adjustment that can be set between 5% and
20% of maximum increase in a pressure recovery attempt. The message
center will flash OPERATOR when this limit is reached and the RPM will not
increase further. The operator must take positive action to restore discharge
pressure. If pressure is not restored within 4 seconds, the pressure governor
will reduce output to the last known output where pressure was maintained.
The operator must input a new setpoint with the INC, DEC, or PRESET
switches. If the pressure rises above the original setpoint and the pressure
governor controls a decrease in water pump engine speed, the pressure
governor will return to normal operations and PSI MODE will be displayed in
the message center.