For efficient operation of boilers, frequent ‘bottom blow-down’ procedures are required to help remove sludge deposits from within the vessel. Sludge may form from dirt in the water supply or from the water treatment chemicals. Where blow-down occurs on manual valves, a safety interlock system must be implemented to ensure that only one boiler blow-down may be carried out at a time. During normal operation, the valve interlock locks the valve in the closed position. Using valve interlocks, the valve can only be opened under strict, controlled conditions.