1602040 - 4" True Union In-line Ball Valve - PVC, Socket, EPDM SealAsahi 1602040 4" PVC True Union In line Ball Valve, Socket x Socket Type 21 21a ball valves are corrosion resistant plastic manual true union design quarter turn valves with hyperbolic flow characteristics, low pressure drops and reliable sealing. They are typically used in on off applications and are offer relatively poor flow control. They are excellent for use in clean fluid service applications with very little to no suspended solids. Type 21 21a