thanks for the response. Not sure which fan I have but it's a fan from the first batch of S7. Do you happen to know if that qualifies?
That would be a 4300rpm fan and you can use it to replace the rear fan of the Antminer S9 which is a 4300rpm fan as well.
The front fan in the S9 is 6000rpm, so if that is broken then you would need to buy a new one.