The Leybold UL 200 Dry helium leak detectors have a built-in dry internal diaphragm backing vacuum pump. The diaphragms inside the dry diaphragm pump need to be replaced after several years of solid operation. This is important maintenance, as good backing pressure is a requirement of the turbomolecular pump inside the Leybold UL-200 helium leak detector. This spares rebuild kit has the replacement parts needed to rebuild the dry internal diaphragm backing pump and has Leybold part number 20099156.