Adapters for a vacuum rack add a Polyethylene component to the list, though. With the PV Tube, sample size is limited to solutions or low viscosity suspensions that can pass through a 0.8mm constriction without clogging. Powder samples, viscous liquids, or course suspensions will clog the valve. Use care when tightening the Pressure Valve. Teflon threads can easily cold flow or strip.
Replacements are readily available if the valve gets damaged.
The Pressure Valve NMR Tube is recommended for studies only over a 40 C temperature range. To study the reaction of an air-sensitive sample with a compound that gets added in aliquots to your NMR tube between spectra, many other valve tubes and sealed sample tubes just won't do. But the Omni-Fit Valve is ideal. It seals with a double protection system that includes a plastic stopcock and septum. Just slip it on the top of a special 5mm NMR Tube.