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I hope that Dave Brierly’s comments can be posted on the forum as well, so that we can all benefit.
I concur that examination of the Pilgrims construction and design will show that it is indeed a pump. 90 psi is not too much of a surprise if the output were to be directed against resistance – ie into a closed pipe such as a pressure gauge.
Nothing has been said in the postings so far about the ports at each end of the plungers, which alternately open and close both inlet and outlet drillings in the body. So, it is a pump at both ends. Also, it is never possible for inlet and outlets to be open at the same time, hence the idea that oil in the bowl is sucked clean by the engine is not possible – it must be first sucked into the pumping chamber through the inlet from the bowl, then pushed out through the outlet into the feed pipe before engine suction can take over. If this were not so then it would constitute a serious airleak and interfere with starting and running generally.
Actually, both sides of the debate are correct because it is both pump and metering device. This of course is due to the adjustable plunger stroke up to its maximum of about 2mm. The problems arise when attempting to reduce oil flow rate to the minimal amount needed for prolonged slow running – idling in traffic or, more seriously, a 10 mile descent of an Alpine pass ( the worst case scenario according to Lofty Avis ). It is impossible for the pump to meter accurately and reliably at such low rates with a stroke of perhaps only 0.25mm. It is this conundrum that led Lofty to develop his revolutionary Loftylube system which allows almost any amount of oil to enter the engine and controls its accumulation inside the crankcase by a scavenging arrangement. Castigated by some as too complicated, it works completely automatically without the need for any adjustment once set up. One grade of oil in one tank constitutes the supply side and there is no need for messing about with oil in the petrol. Very simple in operation. Virtually free of smoke and a clean cut-in on the throttle when opening up after that long descent.