I went for a walk along the Regent's canal at lunchtime, which isn't unusual. I saw boats, which also isn't unusual. But one boat I saw was on the move, rather than moored up, which is unusual. Even more unusual was that I saw a boat actually going through one of the locks, Sturt's lock. I'd not watched a boat go up in a lock for some time, so I decided to wait and watch it.
Once the boat was in the lock, I leant against the beam of one of the bottom gates to get a good view of the crew operating the gates. I don't think I've ever done this before on a lock that is being filled - whenever I've been on a narrowboat I'm either being very keen and operating the top paddles, or driving the boat. Which is why I was a bit surprised by how the bottom gates reacted to the lock filling.
With the lock "empty" the gates don't quite shut properly, and as the top paddles are opened and the lock starts to fill, the incoming water forces the gates shut, pushing them back against the masonary to make a reasonable seal. All well and good, and I've observed this before from afar. At this point the lock gates still leak slightly - thin vertical columns of water coming out from between the middle of the two gates and from the small crack between each lock gate and the lock wall. I'd always assumed that this kept on going, and that locks were inherently slightly leaky.
What followed was new to me. As the lock filled, the gate I was leaning on lurched. At the same point one of the vertical leaks stopped. As the lock filled further the gates lurched again. The remaining vertical leaks sealed. The gates must be deforming and moving slightly under the immense force of the water pressure, and actually moving to create a near perfect seal. What I find most interesting about this is that by making the gates slightly flexible, and making them very loose in their pivots, they actually work better than a very rigid construction in tight pivots.
I'm not sure if all this is only happening because the gates are very new. Sturt's lock's lower gates were replaced last December. Curiously the old gates are still on the BW barge parked at City Road Lock (the next lock up), along with City Road lock's old bottom gates (replaced last November). I can see a reason for not hurrying to dispose of old gates, as I can't think that they're worth anything, but it seems odd that they're tying up a potentially useful barge by storing scrap on it.