The thermostatic mixing valve is needed for when the compressor is still cold (after stop) or when it is running in very cold conditions (winter). When the compressor oil is cold, the mixing valve ensures the oil bypasses the cooler, and recirculates right back into the air-end. This is done to heat up the oil as soon as possible to remove water condensate.
When the lubricant in your air compressor is hot, it keeps any water in your system hot, and therefore in a vapor state. As long as this water remains in a vapor state, it will make its way to the receiver tank, where it can then cool down and then condense back into a liquid (at which point it can be removed with a drain). If the lubricant is not hot, that same vapor will condensate back into liquid form early, and then run the risk of either reeking havoc on your air-end, or go downstream and damage the tools and equipment consuming the compressed air.
Thermostatic Mixing Valves can be installed to hit any number of temperatures before they open up and allow the oil to flow through the cooler. The most common that we have installed for our customers is 158 degrees Fahrenheit (70 C). We opt for the higher Mixing Valve because we find that it reduces the amount of water that flows down stream, and the higher setting will have no negative impact on your equipment.
However, we must caution that all units, facilities and applications are different … and just because we recommend the higher Thermostatic Mixing Valve to most of our customers, that does not mean that we recommend it to all of our customers. Feel free to reach out to our compressed air experts to see what is right for your facility.