Diaphragm

These are found in impulse turbines to create the requisiste number of stages. They locate with a fixed row of blades and are sealed against the rotor shaft by a gland arrangement which must remian effective throughout the working range the diaphragm operates in.
They have a large surface area and so must have sufficient stregth to resist pressure drop across them without being excessively wide which would increase rotor length. Allowance must be made for rapid temperature fluctuations found during manouevring.
Teh take the form of a disc with a row of blades at the circumference and a hole at the centre for the rotor. A horizontal split allows for disassembly, rotation is prevent by a locking plate at the horizontal casing joint.

Methods of Diaphragm fixing

Alternate arrangement

Steam pressure holds the diaphragm plate hard against the downstream face.

Rotor Sealing

Loading on diaphragm = 207 to 280 NM/m², deflection is approximately 2mm

Diaphragm material

In the high temperature regions typically Molybdenum-vanadium steel all parts. More generally a low carbon steel for the nozzle division plates and spacer bands, mild steel for rest. In the low temperature region cast iron diaphragms may be used. Alternatelychromium or Nickel alloy steel may be used