P29 Series Low Pressure Cutout
With Time Delay Relay
The P29 combines a pressure sensing mechanism with a time delay. A drop in
pressure energizes the time delay relay which opens a contact after a
predetermined time period. There are two principal applications for this
control: 1. Chiller Low Temperature Cutout: Pressure element is connected
to the suction side of a chiller refrigeration system and the time delay
relay is wired to the compressor control circuit. Prolonged low suction
pressure, such as pressure caused by a low temperature condition, will
cause the control to shut down the refrigeration compressor. 2. Industrial
Equipment, Oil Pressure Lubrication Cutout: On any electrically driven
machine with a forced oil system, the pressure element is connected to the
lube oil system and the time delay relay is wired in the control circuit.
The control time delay allows oil pressure to build up to normal on
start-up or recover from temporary fluctuations. A sustained loss of oil
pressure will cause the control to shut down the machine.
! CAUTION: Use P29 pressure controls only in
normal indoor environments or outdoors where it is protected from direct
exposure to weather.
All series P29 controls are designed for use only as operating controls.
Where an operating control failure would result in personal injury and/or
loss of property, it is the responsibility of the installer to add devices
(safety, limit controls) or systems (alarm, supervisory systems) that
protect against, or warn of, control failure.
Replaces Part Numbers: P29AC-2
• Heavy duty low profile pressure elements withstand excessively high
overrun pressure that may be encountered in system testing.
• Time delay relay incorporates trip-free manual reset.
• The timing mechanism (time delay relay and terminal board) may be easily
removed and replaced in the field.
• Ambient compensation minimizes the effect of temperature variations at
the control location.
• Simple, single pointer scale indicates cutout pressure.
• Enclosed pressure actuated contacts.
• Single unit mounting and wiring saves installation time and material.
When the equipment is started, the time delay heater is energized. If the
gage pressure does not build up to the "heater off" value within the
required time limit, the time delay relay trips to stop the equipment. If
the gage pressure rises to the "heater-off" value within the required time
limit, the time delay relay will not trip and the equipment will continue
to run. The equipment will be shut down on subnormal pressures longer than
the time setting of the time delay relay.
Time Delay Relay
The time delay relay is a thermal expansion device. "Trip-free" manual
reset models are available with factory set and sealed 60 second time
delay. The time delay relay is compensated to minimize the effect of
ambient temperature variations. Timing is affected by voltage variations.
For applications using a 208 volt control circuit, it is suggested that
one leg of the 208 volt control circuit and a neutral or ground wire be
used to power the 120 volt circuit of the time delay heater. When a P29
control is installed on a 440 or 550 VAC system, use an external step-down
transformer to provide either 120 or 240 volts to the pilot and time delay
relay circuits. The transformer must be of sufficient volt-ampere capacity
to operate the motor starter and
P29 time delay relay.