Low pressure casing for a steam turbine

A low pressure casing of a single shell type for a steam turbine which houses a turbine rotor therein, comprising:

• steam admitting means located in an upper central part of said casing and formed therein with a steam admitting port for admitting turbine driving steam therethrough into the interior of said casing;
• turbine diaphragm means rigidly secured to an inner surface of said casing for supporting stationary blades arranged in a multiplicity of stages axially of the turbine;
• exhausted steam chamber means disposed at opposite ends of said casing axially of the turbine for receiving steam of low temperature and low pressure exhausted thereinto after doing work in the turbine;
• and
• shell means of the casing connecting said steam admitting means to said exhausted steam chamber means;
• wherein the improvement comprises:
• wall means enclosing an outer periphery of the shell means of said casing and connected at its end to said steam admitting means and said exhausted steam chamber means, temperature moderating spaces being defined between an inner surface of said wall means and an outer surface of the shell means of the casing, whereby the temperature differential produced between the outer and inner surfaces of the shell means of the casing can be minimized, and wherein said wall means comprises rings which are frusto-conical in shape and have a larger diameter at one end thereof which is disposed near said steam admitting means than at the other end thereof which is disposed remote from said steam admitting means.