a check valve for use in a pressure balance faucet . it is mainly made up of a control valve body , a check valve block , a pair of positioning pins , two seal rings , a pair check valve sets and a valve mount . the check valve sets are secured to the check valve block which is housed between the control valve body and the valve mount that are in threaded engagement with each other . as the valve sets are worn out , they can be easily and quickly replaced by first dismantling the control valve body from the valve mount and then the check valve block being picked out by pincers to get the valve sets replaced with ease , speed in a diy manner .