In reference to the patent: US5565264
Till which year is the patent valid?
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to find out how long the patent is valid. If you have questions about the status of the patent, go here
Those linked questions and answers provide you with a way to find out. To check if what you find our is right: it's not valid anymore.
This Wikipedia page provides a good review of patent terms in the US. Essentially the term is 20 years from the priority date for patents filed on or after June 8th, 1995 or the longer of 20 years from the priority date or 17 years from the grant date for patents filed before June 8th, 1995.
Unless there were extensions filed (I couldn't find any), the patent should have expired August 29 of 2014.