I fitted one with a valve to my Stuart no 4 so the amount of oil could be controlled, without, I can visualise the steam condensing uncontrolled and displacing all the oil rather quickly!

Alan

The steam enters the oil chamber and condenses only when there has been a change in pressure, i.e. you start the engine. Then when the pressure drops some oil will be expelled into the steam line. If running at constant speed there will be no additional oil introduced. The volume of oil displaced each cycle also depends on the amount of (compressible) air in the reservoir at the start.

It just needs a reasonable one inch or more of small bore tube to tee off the steam line and possibly a jet of 0.010" or 0.020" in the line if it does empty the oil too quickly.

Every respect Duncan, but your version makes less sense. You suggest that steam keeps flowing through the pipe, and any small jet or valve, at the same time as oil flows the other way? Which end of the pipe has the higher pressure? A cyclic system however will follow the inevitable pressure changes in the steam supply. A small bubble of air is necessary to allow that cycle to execute and balance the pressure in the reservoir to that in the steam line.

Yes we all agree that the steam condenses in the lubricator vessel and it is this that displaces the oil. My apologies if I misled by not saying that I agreed with this basic principle at the start.

Our discussion is whether this Simple Displacement Lubricator might be a continuous system or a cyclic one. This lubricator uses the same entrance and exit to the steam line, or steam chest as fitted by Stuart. I suggest that the flow direction must cycle. An experiment would be simple to do – just connect a steam line to it and leave it under pressure, and see if it gradually fills with water and all the oil transfers to the steam line.

There is another configuration sometimes called the Hydrostatic or Ramsbottom style that has a steam inlet, typically from the regulator supply, to the displacement vessel and a separate oil outlet to the cylinders. These do not need to cycle and are effectively continuous. They were developed for use on full size steam locomotives and even included sight glasses to observe the dripping oil flow. If configured to take some steam directly from the boiler they would then operate continuously. They are still used on some model locomotives, especially GWR variants.