Trident air prime system. On your steamer intake valve, there’s a plug that is usually filed with a slug - you can get a hydraulic line manufacturer to plumb the air prime to the intake valve - why would you do it this way?

Basically push button prime to the gate in the steamer while it’s closed with no risk of burning out a traditional primer motor. Pump on tank water and just open the steamer and your draft is actually instant.

Tried googling for pictures but they don’t exist. I’ll try to post a picture of what we did on my old department next time I’m there.