Thoreson-McCosh Inc
EDITION 05/07/10
11
IB201001.doc
SECTION 4.4 SOLID STATE RELAYS & MASTER HEATER CONTACTOR
The Solid State Relay, or SSR, is the accepted way to replace the Mercury contactors.
Since SSRs normally close when they malfunction, a Master Heater Contactor, or MHC, is
installed ahead of the SSR. The MHC is controlled by a safety thermostat, that opens
when the heater temperature has exceeded the maximum controlled temperature. The
Process is 425
F (218
C), and the Regen is 575
F (302
C). To keep the cost of controls
down, on 3 phase heater banks, the center leg of power is not interrupted by the SSR, so
the MHC is also open when the dryer is in the OFF position, this disables all three power
legs
SECTION 4.5 PRECOOLER & WATER SAVER VALVE
When drying a resin below 170
F (77
C), a pre-cooler will need to be installed on the dryer.
There is a water valve installed to control the flow of water. The valve will open when the
air temperature exiting the pre-cooler is 1
F (-1
C), above the Process Set point. There is
an orifice installed in the out port of the water valve, that allows a reduced flow of water
through the valve.
