double ventilator

This is a principle idea of a ventilator. It is just an attempt to reduce the required force, used to deflate the bag because mostly a powerful motor is the rarest part. It makes use of a weight to reduce the force necessary for deflation. Therefore, I guess it flattens the force time course.
marble ball - weight, adjustable in height to set applied force
orange barrel - servo motor
red barrel - fixpoint
purple barrel - connection to servo lever, position adjusts force
gray barrel - spring, optional
Two bags could be deflated at the same frequency if necessary.
A gyroscope on top of the weight could be used as an additional sensor to make the system is up and running at the correct frequency.
The motor could also be set as described here:
https://www.thingiverse.com/thing:4235445
Also, this is just an idea that might or might not help. I’m not a professional mechanical engineer and my physics lessons in school are way back. Adapt it to your plans and test it.