This evening I asked ChatGPT to give me the best way to fill my new 4.7L tank. I told it I have a 9L tank currently at 230 liter and use a GX CS4. I was just going to equalize them then set them off on the CS4 individually.
STEP 1 – Use the 9L tank to partially fill the 4.7L tank (but only up to ~200 bar)
Transfer air from the 9L into the 4.7L, but stop when the 4.7L tank reaches about 200 bar. This will only drop the 9L tank from 230 bar down to roughly 215 bar.
Reasoning:
• You get free air into the 4.7L tank for the lower-pressure portion of the fill.
• You avoid dragging the 9L tank far below 200 bar, preserving its high-pressure utility.
• You avoid wasting a big portion of the 9L tank’s stored energy.
STEP 2 – Use the GX CS4 to fill the 4.7L tank from ~200 bar to 310 bar
Since the 4.7L tank is already past the difficult low-pressure phase, this stage is relatively fast and easy for the compressor.
STEP 3 – Use the now-full 4.7L tank (310 bar) to boost the 9L tank
After the 4.7L tank reaches 310 bar, connect it to the 9L tank and open both valves.
The two tanks will equalize at approximately 246 bar.
• The 9L tank rises from about 215 bar to around 246 bar.
• The 4.7L tank drops from 310 bar to around 246 bar.
This step gives you additional free pressure in the 9L tank before involving the compressor again.
STEP 4 – Use the GX CS4 to top off both tanks to 310 bar
Now run the compressor and fill the 9L tank from ~246 bar to 310 bar, and then fill the 4.7L tank from ~246 bar to 310 bar.
This final stage takes much less time because both tanks start at a relatively high pressure.
Why this method is optimal
- It avoids equalizing a high-pressure large tank with an empty one, which wastes a huge amount of stored air.
- It lets the large 9L tank do the easy, low-pressure portion of the fill where it is most efficient.
- It lets the compressor do only the high-pressure top-offs, reducing run time, heat, and wear.
- It uses the smaller 4.7L tank as a temporary “pressure booster” to recover more pressure into the 9L tank before the compressor finishes the job.