Oil-Free Expanders

Sealing expanders usually involves surfaces sliding against each other (labyrinth seals have parts that do not contact, but their effectiveness is limited). Conventional practice involves adding oil for lubrication of the sliding parts, for example, adding cylinder oil to steam to lubricate the piston rings sliding against the cylinder walls.

Adding a lubricant causes a number of problems. In the following, the term 'oil' will be used to represent lubricant: Some examples of running without oil are:
 * The oil must be purchased and supplied to the engine. The system must have equipment to meter and supply the oil to the engine, increasing system cost and complexity.
 * If exhaust steam is condensed, the oil must be removed first or it will foul the condenser surfaces and greatly reduce condenser efficiency.
 * If the exhaust steam is vented to the environment, even more stringent requirements for removing the oil are needed.
 * Oil in the feed water will similarly foul the heat exchanger surfaces in the steam generator, also reducing efficiency. When the thickness of the fouling builds up, the tube wall no longer is cooled by the water/steam inside and the metal temperature rises.  At some point the tube weakens from the heat and bursts.
 * Running higher temperature steam to gain efficiency can also cause the oil to 'coke', that is, chemically break down leaving a carbon residue. This can happen in valves and piston rings, reducing sealing and increasing wear.

Skoda Works, Czech Republic, circa 1945
Was reported to have run a 440 hp steam engine without cylinder oil. This was attributed to the paper:

H. Frank and J. Rais, "High Speed Steam Engine Without Lubrication", The Engineer's Digest, 2, 516 (1945) (Note that this journal was not the one of the same name published by the U.S. Coast Guard.)

as reported in:

Aerojet-General Corp. (1968). CONCEPTUAL DESIGN OF AN IMPLANTABLE RADIOISOTOPE POWER SOURCE FOR CIRCULATORY SUPPORT SYSTEMS''. Final Technical Report.'' United States. doi:10.2172/4509689 Appendix P, which contains the calculations and example of designing a steam engine.

J. Rais also obtained US patent 2153025 "Packing ring for sealing the pistons and piston rods" in 1939 describing rings of carbon-graphite bonded to steel backing rings.