Where and how you take a thermal fluid sample can make all the difference in what the test results reveal.
Where a sample should be taken is simple – any location where there is flow and the temperature is above 180°F. A blowdown valve on the pump suction strainer housing is a good bet since that’s where you’ll find the lowest pressure and temperature in most systems. Piping drain valves will work as long as you purge several containers worth of fluid before taking the sample. Expansion tank or thermal buffer tank drain valves are tempting as a sample location because they are (usually) cool and (mostly) accessible. Don’t do it. For a long list of reasons, it’s almost the worst place to take a sample, just above scooping it off the floor near the pump.
Taking the Hot Oil Sample
How to take a sample is not quite as simple. Why? Because improper sampling practices can actually alter the physical characteristics of the sample that will be measured.
Ideally, a sample should be taken directly into a glass sample jar so any contamination or carbon in the fluid is easy to measure. The problem with glass is that it can shatter if the sample is taken too hot (above 250°F). So if the next heater shutdown isn’t scheduled until the Phillies win the pennant, install 18-24” of ¼” copper tubing on the sample port and bend a loop or two through a bucket of water. This will knock the sample temperature down the couple hundred degrees needed to keep the glass from breaking. Or take the sample in a clean metal can with a screw top and send that in (just remember to label it with the system name and date). Do not take the hot sample in a metal “cooling” bucket and then transfer it to the sample container.
Improvised Fluid Sampling Cooler
See Paratherm’s one-minute video on fluid sampling and testing here —
Heat Transfer Fluid Sampling