The plumbing in my place is a bit on the crap side, and one deficiency is the hot water supply. I have one of those shite combination cylinders with a diddy little header tank sat on top of a diddy little hot water cylinder, the two separated only by a thin sheet of copper. It is a little suboptimal...
The small capacity of the tank means I have to set the thermostat to "sodding hot" in order to be able to fill a bath without running out of hot water. Copper being somewhat deficient as a thermal insulator, the header tank gets as hot as the hot water cylinder, and the expansion of the water as it heats up means the float ball for the ballcock ends up almost submerged in near-boiling water.
Then when I use some hot water, the level drops, the ballcock opens, cold water rushes in and the temperature of the header tank drops sharply. The hot water tank also cools, the thermostat kicks in and heats the whole lot back up again. The cycle repeats every time I use some hot water.
Over time the thermal cycling causes the plastic float ball to crack. It then sucks in water through the crack until it is absolutely full with only a very small air bubble, at which point its large reserve of buoyancy is exhausted, it sinks, the ballcock remains permanently open and an overflow is the result.
Being a pigeon I find this shite design, with its inevitable and predictable failure for no good reason, intensely annoying. It's also interesting how the ball, which generally cracks somewhere about half way up, manages to suck in water through the crack until it is absolutely full. It was in thinking about this phenomenon that the solution occurred to me: make it work the other way round, make the ball empty itself instead of filling itself up.
And thus was hatched the idea of Pigeon's Self Purging Ball. I drilled a hole at the uppermost point of the ball and inserted a tube reaching nearly to the bottom of the ball, then sealed around the tube with hot melt doggie, which is one of the few substances that at least makes a pretence at adhering to the high-density polyethylene of which the ball is made.
When the temperature rises, the contents of the ball expand. Because the end of the tube is at the lowest point of the ball, the pressure rise inside the ball forces any water which has found its way into the ball up and out of the tube.
When the temperature falls, the contents of the ball contract. Because the outer end of the tube is above the water level in the tank, the falling pressure inside the ball draws in air, which bubbles through any remaining water to be trapped and assist in expulsion of the water when the temperature rises again.
So there you have it. If you too have a repeatedly-overflowing shite combination cylinder then you too can fit it with one of Pigeon's Self Purging Balls. All you need is a few inches of rigid or semi-rigid plastic tube a quarter of an inch or less in diameter, a drill, and some hot melt doggie.
