It's a lot more complicated to modulate the pressure. You need to titrate the pressure to each patient/setup, and often inhale vs exhale. Motor with ESC? Easy.

It's a lot more complicated to modulate the pressure. You need to titrate the pressure to each patient/setup, and often inhale vs exhale. Motor with ESC? Easy. Solenoid valve has only on/off, so you have to manually tune a pressure valve for each level. Also the pilot kind like those in sprinkler systems don't work well with low pressure air.