US Patent 7165570 Pressure balancing cartridge for mixing valve

A pressure balancing cartridge for mixing hot and cold water includes a casing having a sleeve therein which further includes a reciprocating balancing spool therein. There are seal members positioned to form a seal between the sleeve and the casing. Further, a spring is incorporated to protect a balancing spool of the valve from “water hammer” shock and to mechanically shear and digest any deposited matter in the area of the spring. Still further, by using material other than stainless steel, failure of the balancing spool is eliminated in “bad” water environments.