Isolation steam valve with atmospheric vent and relief capability

An isolation steam valve arrangement for use on the exhaust side of a steam turbine for directing exhaust steam therefrom to steam operated auxiliary equipment and for relieving or venting steam to the atmosphere. The valve arrangement includes a casing, or body provided with a single inlet and plural outlets. A main valve between the inlet and one of the outlets is selectively positionable from fully open to fully closed for controlling steam flow through one outlet for operating auxiliary equipment. A normally closed vent valve between the inlet and other outlet is adapted to open upon closure of the main valve to establish open communication between the inlet and other outlet in order to continuously vent to the atmosphere a low volume of steam from upstream of the main valve. A normally closed pressure operable relief valve is adapted to relieve to the atmosphere a high volume of pressurized steam from upstream of the main valve.