I am not aware of a limit in the event pipes. There is neither a limit in the number of event pipes nor in the size of the event pipes. You should only make sure that you take the events in a reasonable time.
The mechanism in the PI API is different (being called sign up for updates / sign up for exception reports), however, similar to above there should be no limitation as well. Please note that vCampus can not provide any support on the PI API.
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