How long do they last and how often do I need to check them?

 

It depends on a few things. Are they being used with a progressive controller? How often is the nitrous kit used? It's pretty easy to open the solenoid and take a look at the seal. If using a progressive controller regularly I would look at them every few months. Maybe at every oil change crack open the noids and take a look, only takes a few minutes.

Matt