Any idea about the technical evaluation criteria for Steam Conditioning Valve (let down valve) that will reduce the steam pressure from H.P. to M.P.?

 

Sounds like a pressure regulator.

From this page, http://www.lesman.com/unleashd/catalog/valves/Jordan-Mark-66-pressure-regulator.html

Click on the link to the <b> <i>Process Regulators Application Data Sheet</i> </b> for a fill-in-the-blanks sheet with selection criteria for a pressure regulator.