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A patent might be renewed by the owner. You should verify whether that was done.
Also, whether someone made (perhaps minor) modifications to the initial patent and now holds a current patent for his concept, though it may be similar to the initial patent, and even after the initial patent expired.
Do you mean that patents can be perpetual? We are planning to use ideas from a patent 25 years ago and add some additional details to make a newer product. Will that hurt us? Has anybody done this way?
you need to hire a patent attorney, patents last 18-20 years, they can be modified and a new patent issued to take account of the modification - however if your equipment only uses methods from the original patent - you should be safe. There may well be other patents issued for the same thing - this some times happens - this is why you hire a patent attorney firm to do a thorough patent search, to see if there are duplicates, or very similar patents out there ...