The article describes the work of one of the basic units of the chlorinator of ejection (vacuum) type - water pump (ejector). We justify the choice of the ejector parameters that characterize its performance. The problem of determining the chlorine absorption is solved; we showed that it depended on the parameters of the ejector and on the characteristics of an aqueous solution that allows you to ensure the accuracy of dosing of chlorine gas and eliminate the possibility of an overdose.