Abstract: Hot oil pumps of atmospheric and vacuum distillation units originally used equilibrium mechanical seals in Henan Oilfield Refinery,which were replaced by bellows mechanical seals later.But bellows mechanical seals were finally modified to nange-barrel -type seals because the high pressure ends were liable to leak and service life was short.Rolling bearings were replaced by sliding bearings made of copper impregnated graphite,thus dynamic seals with several seal points were changed into static seals with one seal point.