It’s been several decades since I last saw water-seal bell spirometers being used in a Pulmonary Function lab. They have been displaced mostly by systems that use flow sensors of one type of another and the small handful of equipment manufacturers that still make volume-displacement spirometers use rolling seals. This isn’t to say that this kind of spirometer isn’t being manufactured any more and in fact there appears to be a modestly thriving market in water-seal spirometers intended for use by students.
In the low-end of the market (under $1000) there are several different systems that would likely never make it into a PFT Lab. None of the manufacturers or distributors provide any claims about their accuracy and considering they are mostly made of injection-molded plastic it is hard to see what level of accuracy they could ever offer. Moreover, the volume readout for these spirometers is a dial that is moved by the chain attached between the bell and the counter-weight. The gradation on these dials allows you to measure (somewhat optimistically, I’d say) differences in exhaled volume of 0.1 liter.
