A ball valve apparatus includes a housing defining a housing inlet and a housing outlet and a valve cartridge mounted within the housing and defining a cartridge flow path extending between a cartridge inlet and a cartridge outlet, wherein the cartridge inlet is arranged in fluid communication with the housing inlet and the cartridge outlet is arranged in fluid communication with the housing outlet. A ball valve member is mounted within the valve cartridge and is rotatable to selectively open and close the cartridge flow path. A leak chamber is defined between the housing and the cartridge for containing fluid leakage from the valve cartridge.