PG25 is a mix of roughly a quarter propylene glycol and three quarters water, with an inhibitor package to protect the metals in the loop. The glycol content helps limit biological growth in a sealed system; the inhibitors protect wetted surfaces for the service life of the fluid.
Points worth writing into the specification
- A fluid approved by the CDU and cold-plate manufacturers for the hardware being installed
- Pre-mixed fluid rather than site-mixed, so concentration and water quality are controlled
- A certificate of analysis with every batch, tied to the loop it went into
- Compatibility with the seals, hoses and wetted materials in the loop
- A sampling plan after the fill, and a top-up of the same fluid
Logistics
Bulk first fills are usually delivered by ISO tank, with IBCs and drums for smaller loops and top-ups. Fluids from different manufacturers should not be mixed without the hardware makers' approval, so the top-up stock should match what went in on day one.
