Normally city pressure has adequate flow and pressure to flush out the system.
Occasionally, a booster pump is needed in the "fill" line, to push the water to the top
of the system. If possible, flush the loop on a cloudy day to avoid thermal shock of
Flush the system with city water until the fluid coming from the "drain" fitting is dear.
Make sure the water is moving through all parts of the loop. On a sunny day, all the
collectors should be at the same (fairly cool) temperature.
Turn off the water, disconnect the fill hose, and allow the system to drain. Drain out
any dead legs. Small amounts of "hung-up" water in the loop can be flushed out
during recharging. Dispose of used glycol properly, according to local regulations.
Automatic Water Make-Up
If glycol-filled loops are equipped with automatic water make-up, dose gate valves,
if possible, and tag them so they will remain closed.
Draining and Flushing Oil Loops
In many cases, foreign matter and small amounts of water can be filtered out of the
oil without draining it all out. Use a hydraulic fluid filter on a charging system as
shown in Figure 5-27.
If it is necessary to drain the system, a drain port should be in place at the lowest
point of the system. Open and drain the used oil.
Small amounts of oil hung up in parts of the loop that are in the flow can be left
undrained. However, fluid in "dead legs," such as expansion tanks, must be drained
out. This may require cutting into the piping or unthreading joints, but it must be
done to avoid contaminating the new fluid.
Oils will burn when exposed to soldering torch flames. Always drain
the system before unsoldering joints! Before heating the joints,
mechanically open the loop, to allow fluid vapors to escape. As the
joint comes apart, be prepared for a brief flare. Keep a fire
extinguisher with you- not out in the truck!
5.2 REPAIR PROCEDURES