This is from the instalation guide for Wartsila 20 engine of about 1600 HP. HT is High Temp, or the jacket water side, the LT is for the intercooler side, with both systems being independant of each other. #7 is the Orifice , or Ajustment Valves we use to slow the flow. I'm not sure what the need for a second one would be when the Thurmostat is closed and the water is by passing the cooler but the call for one.