Shower faucets are usually sold as “shower valve sets ” (including the valve, the control lever and cover plate, and the shower head). Most plumbing codes now require new installations to be equipped with a pressure-balancing spool.Usually this is part of the valve itself (the part that is built into the wall).

The pressure-balance function is to maintain relatively even water temperature to the shower head, even when other nearby water demand happens – such as a toilet flush or an appliance start-up. So no more need to jump out of the way of a blast of very hot or very cold water.(Pressure-balanced valves are sometimes called “anti-scald” valves.)