Need piston & piston ring design for steam cylinder, and blow-by calcs

I work in a plant that uses steam powered forging hammers to forge red-hot steel into various closed die forgings.  The hammers we use range from 12,000 lb. to 50,000 lb. Erie forging hammers.  The piston sizes range from 22" OD and up to 44" OD.  Each hammer piston uses two piston rings to help prevent blow-by on the piston.  The amount of stroke of the piston ranges from about 36" and up to 68".  Our current piston rings are made from injection molded 25% carbon/graphite filled PTFE.  The steam forging hammers operate using up to 120 psi steam at 350*F, and the steam cylinder is lubricated with oil when in use.  The steam cylinders are sleeved using a cast iron metal, and the original piston rings that used to be used in these hammers was some type of steel that looked like it was rolled into shape.  I am trying to find a better piston ring design to limit the amount of blow-by in the steam cylinder.  Is there something better to use than the PTFE ring?

Note: We are planning on rebuilding the steam cylinders with new sleeves to eleminate any problems with wear on the sleeves.  Our quickest and cheapest fix right now is to design a better piston ring.

I also have been trying to establish how much steam loss we have through blow-by of the piston.  I have been unsuccessful in finding formulas that can calculate blow-by, other than using a calculated area based off of orifice calculations.  I need formulas that can accomodate the initial steam pressure, the loss from blow-by, and any effects from back pressure in the exhaust.

With this informatin, I can establish a cost justification for repairing the steam cylinders.

Any help would be appreciated.