TOOK (Customer) asked a question.
What are the pros/cons to a solenoid spool valve that uses rubber (NBR) seals versus metal seals?
Application is using regular shop air to actuate air cylinders at room temp at 60 cpm for millions of cycles. The SMC VFS series has metal seals. I have been using Norgren V61 series and trying to improve longevity.
I'm guessing when you write metal seals, you mean lapped spool and sleeve? A con with lapped spool and sleeve is your air MUST BE dry. A second con is - depending on where you plan to mount them - it it best that they're positioned so the valve spools move horizontally. This is due to the spools tending to stick in the down position when not in use over a time period (my customers called this "Monday morning blues" after non-use on a weekend). A third con is they tend to have a lower CV rating.
So, you can probably gain I prefer rubber seals. I have used quite a few of the Nitra AVS valves (since 2015) in non-lubed applications and - so far - have not had to replace a one. Rubber seals are more forgiving to the things you find in compressed air: water and oil. And as long as you don't introduce Marvel Mystery Oil into your pneumatic system, should last a long time.
Good luck!