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The stems ( 3 ) are made in 13% Cr stainless steel, even if they are never in contact with the fluid.
This to:
- Prevent the oxidation of the stems, when the manifold is installed in the open air.
- Obtain a difference in hardness to avoid seizures between the stems and the bonnets.
The connection of the stem and the piston ( 4 ) is a " T " type:
- The " T " shape prevents any disconnection of the two elements that may be possible in case of joint made by threaded bushings.
The pistons are made in Austenitic Stainless Steel, and after accurate machining, they are cold rolled in order to:
- Increase the surface hardness
- Obtain a very smooth surface ( RA = 0,2m ).
Also :
- The sealing rings are made in reinforced graphite ( valve ring above 6 ) and in graphite interposed with thin stainless steel plates ( valve ring below 7 ).
- The hand wheels have a large diameter for a better manoeuvring of the valves
- The diameter of the piston is 15 mm.