Cutaway reproduction of Elijah McCoy's first patent

Notes on Operation and Manufacture of the "McCoy Lubricator"

The artifact displayed here is a recreation of the first invention patented by Elijah McCoy in 1872. This device was the first to use the pressure of the steam within a steam engine to regulate the amount of lubricant dispensed into the cylinders, thus eliminating the need for frequent filling.

This "self-regulating lubricator" is designed to be screwed into the head of a steam cylinder. During operation, steam pressure acting on the piston pushes the valve stem up, raising the washer off the valve seat until the top of the valve stem strikes the flow adjustment screw. This permits some oil to run down into the space between the stem and the valve tube. At the same time a small amount of steam seeps around the piston in its bore and escapes upward around the stem and tube, ending up inside the oil reservoir. As the steam cools, it condenses on the hemispherical cover and runs down the sides of the reservoir. Oil is less dense than water, so the condensed steam fills the bottom of the reservoir, pushing the oil up high enough to keep it above the valve seat. When it is time to refill the reservoir, the drain valve is opened, allowing the water to run out while safely venting any remaining steam pressure. The drain valve is then closed, the cover is removed, the oil level is topped up, and the cover replaced.

When I decided to duplicate this artifact, the only information I had available was a copy of the original patent drawing. This was measured and scaled up by a factor of two. While the main body of the original device was probably made from a brass or bronze casting, I used a wrought aluminum alloy (6061-T6) round bar four inches in diameter and about ten inches long. This was turned, bored, and threaded using the lathe in Engineering Technology Machine Shop.

The valve stem/piston was made from a mild steel rod, again turned on the lathe. The valve tube was made from a piece of aluminum aircraft tubing that already had the right internal and external dimensions, so it was simply cut to length. The cap was made from a short section of the same bar as the main body. Cutting the hemispherical surface on the bottom took several hours and numerous cuts with specially ground tools before I was satisfied.

The drain valve, flow adjustment screw and nut, and valve washer were made from a red brass alloy of unknown vintage. The only purchased parts are several nuts and the coil spring used to keep the valve closed.

After the object was assembled, it was "sectioned" to make it easy to see the inner workings. Following a good deburring and some final surface preparation, using Birchwood-Casey's Alumiblack compound artificially aged the aluminum parts. The other parts were darkened using several different types of cold bluing compounds.

There is more than forty hours of machine work and hand fitting in the finished artifact. I thoroughly enjoyed the process of recreating the seminal invention of one of the finest mechanical engineers of all time.

Keith G. Benedict

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Last Modified: February 9, 1999