Tottenham ct rd has floodgates on both the central and northern lines. When i worked there about eleven years ago all the original equpment was still in situ.
The air cylinders had some air left in them and it was possible to operate them i assume by this method. But in the tunnel there are emergency release leavers if the other equipment doesn't work. This simply releases a catch in the tunnel roof and then gates hinge down from the roof closing the tunnel.
Before the intro of the 95 stock there was the northern line project to repair a few things for the new stock. As i remember there was a fear that the gates would one day unlatch themselves through vibration so a piece of metal was bolted to stop this.
Not sure if this was doen to the central line. i also understand that the gates at waterloo do still work if wanted to after a few checks. repairs etc.