1928 Crossley OE128 The replacement used fuel injector. As the replacement injector has a better atomisation than the original injector and definitely higher NOP ( nozzle opening pressure) as you couldn’t get it to atomise by just pulling the priming handle without an extension ( tube) on the handle we thought we’d better try and determine what the NOP is and if the non return valves are sealing in the pump. If the non return valves aren’t sealing in the pump every time the pump pumps it has to