It's a vintage pen, and the word "英雄616" (Hero 616) can be seen on the metal cap.
The built-in ink sac is able to hold quite an amount of ink.
Now, I'm going to load this maroon Hero 616 with Pelikan 4001 Brilliant Brown:
1. Remove the metal cap that covering the ink sac.
2. Compress the ink sac completely before lowering it into the bottle of ink.
3. Release the ink sac to allow the ink to be suck in.
4. With the feeder still inside the ink bottle, completely compress the ink sac again (slowly) for another 2 more times.
5. Do 3-quick compress on the ink sac to allow maximum suction of ink into the ink sac.
6. Done. Clean the excess ink on the pen.