This is another component which normally remains unseen. It is an air chamber from the connection of a water crane provided to supply locomotives with water.
When the feed-valve of a water crane is opened, considerable pressure may be built up on the pipes behind it by the inflowing water, and damage them. The air chamber is designed to absorb this pressure wave and effectively to act as a shock absorber. The parts painted blue are normally situated underground. Only the handwheel to open and close the feed-valve is seen projecting above ground.