Jabsco or Generic impellers flexible impellers are subject to rigorous quality testing to ensure reliability and performance. Impellers should be replaced at least once every year or sooner depending on engine duty. Always carry a spare ! NEOPRENE is the most commonly used material and is the toughest, longest wearing compound. However it is suitable for use only when a small amount of oil or diesel is present in the water. NITRILE offers better resistance to oil and diesel fuel, however performance and life is reduced by about 10%.