World Leaders in Ultra-Pure Heating
Revision 10
www.heateflex.com
01/17/13
405 E. Santa Clara St.
Arcadia, CA 91006-7218
Tel: (626) 599-8566 Fax: (626) 599-9567
5.0 Preventive Maintenance and Servicing
CAUTION - CAUTION - CAUTION
All servicing on the system must be done with the unit completely cooled down, not under
pressure for D.I. water or steam, both upstream and downstream and off-line electrically,
unless otherwise noted.
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5.1 Process Control System
The only servicing required for the control system is to verify sensors and to recalibrate the
temperature-control look-up table if there is evidence of poor temperature control or a new set
point temperature has been entered which is 15°C above or below the previous value. This
process is described in Section 3.2.3 of this manual.
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5.1.1 Thermocouple Temperature Sensors
There are four Type J thermocouples (TC) on the unit - one TC for the process D.I. water
temperature, a second TC for the cold D.I. valve input temperature, a third TC for the hot valve
D.I. input temperature, and a fourth TC for measuring the steam temperature within the
exchanger vessel.
Generally, a thermocouple‟s accuracy does not degrade over time and replacement should only
be necessary if it shorts out or open circuits completely. In addition, the repeatability between
thermocouples is excellent so calibration will usually not be required on the instrument.
Since these thermocouples are used as inputs to the PLC‟s temperature control and safety
system, the process temperature and steam temperature readings are indicated on the Systems
Status screen. The indicated values can be compared to direct-reading thermometers on the unit
to determine if one or the other component may be faulty. The process thermocouple is located
inline to a dial thermometer fitted in the PVDF piping on the front side of the unit‟s plumbing
and the steam thermocouple is mounted on the exchanger shell along with a dial thermometer.
The cold valve and the hot valve thermocouples are located respectively on the PVDF piping
and measure the respective temperatures of the incoming D.I. water before mixing occurs. The
cold valve input temperature value is displayed along with the process temperature value and
steam temperature value on the Recalibration screen.
