Hello. I'd like to know which material the best for the NRV inner seal? Leather like the old time, or rubber? What the Sha ideal for this function? I tried leather but it doesn't close well, i tried rubber (70Sha) it was too hard doesn't close well too. Roy.
Hi Roy, they used cork or Buna rubber for the NRV earlier. Leather was only used for the pump. You can try Viton as it will reliably withstand white gas / petrol or kerosine / paraffin, but I don't know which SHA. Perhaps you can try gaskets from spare cans, you might get them as replacements. BR, Martin
Hi Martin. The cork is a good idea, i'll try it. Maybe the old nrv seal was cork, just i belived that is leather? Roy
Hi Roy, it might be difficult to make one from cork yourself. The surface has to be perfectly even/plain and without any defect. Otherwise it will fail to seal properly, resulting in leaking fuel. Almost all of the old PX/Hasag/Ditmar lanterns I restored so far had a stuck or leaky NRV and were cured successfully by inserting a new piece of Viton (made by a hole-punch out of a sheet). BR, Martin
I don't think lamp manufacturers have used cork for about 80-90 years - far superior materials are available e.g. Viton.
To my experience from fettling German/Austrian lanterns cork was used for NRV gaskets until shortly after the war. It has superior durability and resistivity against all kinds of fuel. Buna (styrene-butadiene rubber) was patented in 1929 (produced in big scale from late 1930s) and was used mainly for filler cap seals and gaskets since then. Before that leather was used, like for the pump until recent time. Buna deteriorates with fuel; Viton (fluoroelastomer) is better, but was invented not until the 1950s.
Thanks the answers! Finally the VITON is the best material for NRV gaskets. I'll try it. What version is the best? Punch from a viton plate, or buy a viton cord? Roy
Probably the most economic way is to buy a couple from the Fettle Box. Otherwise you'll have to buy a sheet of Viton and it's very expensive...
