bm_c1a4e Doors won't open!

Hi
I am in c1a4e (as named in the save logs) and am stuck. I haven’t played Half-Life 1 for long time and have forgotten the name of the level, sorry!

So I killed the three tentical creature and went down into the pool of water, swam down then up to a ledge and came to a room with a fast running radiation river. There is a spinning gear in the acid water in the middle of the room. I have explored the room and found 5 doors in total and NONE of them will open!:[

When I try to activate the doors nothing happens and therefore I cannot proceed. I can jump everywhere fine and am not having any trouble reaching places, it’s just the doors won’t open! I can’t solve the puzzle behind this.

Am I missing something or is this a glitch? I would be very greatful for any help!

HINT:
Take the pipe path

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