Edwards TCU 40/80 - Page 16

4.2.2 If cooling is not required:
1. Solenoid valve SVl closes (coil de-energized).
2. Hot refrigerant from the compressor is passed through SV2 (coil energized) and a hot gas bypass
valve before returning to the compressor suction line. This bypassing allows the compressor to run
continuously.
3. Cooling, required to prevent the compressor from overheating, is provided by allowing some of the
liquid from the condenser to pass through the safety cooling automatic expansion valve into the
suction line, thus maintaining the discharge gas temperature below 99 °C.
4.3 Coolant circuit
Coolant is pulled from the reservoir by the circulation pump and transferred to the heat exchanger where
it is cooled by the refrigeration system as required. It then flows to the process equipment by means of the
coolant supply hose.
The coolant returns to the TCU 40/80 reservoir by means of the coolant return hose.
The coolant system requires 8 liters of coolant for the reservoir, plus the volume of the circulation lines
and any other spaces filled with coolant that are attached to the TCU 40/80.
To increase the coolant temperature, the reservoir uses an electrical resistance heater that is controlled by
the temperature controller. The heater must be fully submerged at all times, and if the coolant in the
reservoir falls below 3.S liters, a level switch causes the status alarm signal to automatically shut down the
TCU 40/80.
A three-float level switch, a thermostat, and a flow sensor provide coolant status signals to the TCU 40/80
control system.
4.4 Temperature monitoring
A Resistance Temperature Device (RTD) monitors the temperature of the coolant leaving the TCU 40/80
and transmits this information to the temperature controller. The TCU 40/80 compares the output of the
RTD to the selected process temperature (SVl) and determines if the coolant needs to be cooled or heated.
The temperature controller then operates the main cooling solenoid valve or heater.
The coolant temperature at the supply port on the rear panel is measured by a local, internally connected
RTD. If sensing of process equipment temperature is needed, connect an RTD to J72J3 at the rear panel
(see Figure 5 on page 13). For remote connection schematic details, see Figure IS on page 56.
^WIITV
10 TCU 40/80 Temperature Control Unit