It would be great to know what it is, how it works and how it differs from the conical valve used now, as well as the motive for the switch to conical

The next bridge up-river from Tower Bridge is London Bridge, at the south end of which is Borough Market. This is an assemblage of fruit, cheese, bread etc stalls, of high quality, and is worth a visit on its own. Adjacent to the market (west side) is one of Monmouth Coffee's outlets. Monmouth was sourcing, roasting and serving high quality