The tank shall contain a standing charge of fresh water, equivalent to the amount of water which would be discharged in one minute by the pump referred to in paragraph .12, and the arrangements shall provide for maintaining an air pressure in the tank such as to ensure that where the standing charge of fresh water in the tank has been used the pressure will be not less than the working pressure of the sprinkler, plus the pressure exerted by a head of water measured from the bottom of the tank to the highest sprinkler in the system.
Mahuti peab sisaldama mageveevaru, mis võrdub veehulgaga, mille väljastaks punktis 12 nimetatud pump ühe minuti jooksul, ja seadistused peavad ette nägema mahutis surve säilitamist, mis tagab, et kui mahutis olev mageveevaru on kasutatud, ei ole surve väiksem kui sprinkleri töösurve pluss surve, mida avaldab mahuti põhjast süsteemi kõrgeima sprinklerini mõõdetud veesammas.