On most high power UHF, some VHF and some FM transmitters, the transmitter’s “residual transmission heat” is dissipated by liquid cooling systems.
Here in the US, it is very common to use a mixture of distilled water and Propylene Glycol (“Glycol”). The mixture varies based on the environment of the transmitter and the location of the external cooling systems (heat exchangers).
Glycol is used because it will prevent the outdoor systems from freezing. It also prevents the water from boiling when transferring heat. Glycol is a nasty substance if you have to handle it, with an invasive pink dye, which is very difficult to wash out when dried, and a perfume agent that is pungent at best. However Propylene Glycol is considered non toxic. (Unlike Ethylene Glycol, which is used in radiator fluid and plastics manufacturing.). Glycol is a chemical that can leave behind residue, which over time, especially when mixing with water, can cause the pH balance and other properties of the glycol to change. This breakdown of the elements of the glycol, causing deposit buildups in both transmission components and the cooling system itself. It is important when using a piece of transmission gear, that this chemical be tested every other year, to determine if it needs to be changed out before that damage occurs.
We take the sample using the drain port on the IOT tube bottom.
This is done by running the fluid into a small bucket for about 15 seconds to flush out the crusted contaminants. Then using the sample container, we fill it slowly with the fluid.
The company we use, Dow Chemicals, provides the sample containers to put the samples in. They give you documentation and a little box to ship the samples out. Because we have two discreet cooling systems, two samples of the chemical are sent.
In a few weeks, we will get the results, and based on the results, will determine if we need to flush the entire cooling system and replace the Glycol in it.