I have been scratching my head lately over slow boil times in some my stoves (111, 210, 41 Sport, Fuhrmeister 8 etc.). After servicing the stoves (new pump cups, graphite washers, cap seals, NRVs and jets) many of my serviced stoves boils a liter of water from 13C in about 7-12 minutes, depending on the stove. All boil tests are done indoors with a medium diameter kettle with lid. High quality kerosene is used. I use Viton pips from Fettlebox, and sometimes complete NRVs from Juliands/Tilleylampandstoves (Indian made?). Always with new lead washers. In one instance i gave my Fuhrmeister 8 a Fettlebox Viton pip. I was not able to pump up high pressure, so i switched the NRV with a complete NRV from Juliands. It worked much better, but still a bit anemic. Pump cup was brand new from Fettlebox. There are no signs of leaks in the stoves mentioned, and i therefore wonder if the relation NRV spring-NRV pip might affect the ability to pressure the stove?
Do you mean you couldn’t force air into the tank or that the NRV didn’t hold the pressurised air in (pushing the pump rod back out)?
@Countdown That’s not a symptom of too weak a NRV spring however. It suggests a shortfall in pump cup efficiency in trapping and compressing a charge of air. Discussed here: How oily is your pump cup leather?
A weak spring will make it easier to force air into the tank. So as long the spring is not too weak, so it leaks, a weak spring will let you make higher pressure.
