My eye was taken by the Enots “Best” Crankcase Pressure Relief Valve – the first image and description of it that I have seen. Originally brought to my attention by Tim Sharp as he used a couple in his version of Loftylube.
Obviously ( I think! ) designed to relieve crankcase pressure in a four-stroke engine without also blowing out oil, its use in a two-stroke scavenging system would require it to blow out excess oil with a minimal loss of pressure – a very different application. The valve is positioned quite differently in the two engine types – high up the crankcase for a four-stroke and right at the bottom for a two-stroke.
I have tried similar spring loaded disc valves in my long search for a viable Loftylube system. Like almost any non-return valve design, they do work well with a bit of throttle opening. Problems arise on a closed throttle when crankcase pressure fluctuations and gas-flow are very small indeed. In such a worst-case scenario any valve can stick closed – the so-called “cracking pressure” being too high. The engine can then start accumulating oil which later gets carried into the combustion chamber in a big ‘swoosh’ creating the well known smoke screen.
The Enots disc valve has a large surface area of contact when closed and with the presence of oil may be stuck by surface tension. The modern elastomeric duckbill valve is designed to be “normally open” so has virtually zero cracking pressure. It also closes very rapidly with almost nil suck-back when the pressure reverses. This may make it the design of choice for two-stroke scavenging and I am experimenting with items designed and made by the Dutch MiniValve company. So far they seem to be ideal, but longer term testing is required.
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