Taken from a random chlorinator manual might explain your question 'WARNING: It is essential that pipe work and equipment do not allow gases generated from the cell to collect and build up. WARNING: Cell must be installed vertically with water connections pointing downwards - this creates a safety gas trap. Installation in any other way may cause explosion, injury or death. WARNING: Cell must be installed in the return pipework to the pool. Always install after filter, gas heater, solar heater or heat pump connections. WARNING: DO NOT install isolation valves on inlet or outlet of cell.'
