So, how does the blow down separator manage that temperature reduction? The first step is the creation of flash steam in the centrifugal separator. When the high pressure hot water comes into the blow down separator pressure vessel it hits a striking plate and droplets form. A portion of the water changes to flash steam due to the pressure drop. 10-20% of the water, depending on the initial boiler pressure, can be converted to flash steam which is vented to the atmosphere. The water that remains after the steam is created will be at 212 deg. F, and it still needs to be cooled to a minimum of 140 deg. F. by the after cooler before it can be dumped into the drain. The main issues with creating the flash steam are having enough volume in the pressure vessel to handle the steam without building up pressure, and making sure the vent piping is large enough to handle the high flow rate of flash steam.