The aneroid cell pushes on the core, pressing it rearwards into the coil. A spring provides an opposing force and presses against the back of the case.
The center of the lower aneroid cell has a curve recess for a “bumper” to fit into.
This section of parts is disassembled by placing a square bit into the corresponding hole and then using a wrench on the bolt that mates with the spring.
The vacuum port on the back of the MPS has a small plastic baffle to stop soot getting inside. The baffle is a disc with a small hole and is held in place by a thin strip of metal. It is possible to slightly pull up on the metal strip and remove the baffle.
When a vacuum is applied the pressure inside the body of the MPS is reduced, including around the aneroid cells. The inside of the aneroid cells are at ambient pressure creating a pressure differential, causing the aneroid cells to expand. This expansion pushes on the core inside the coil moving it backwards.
Case changed to clear plastic to show how the baffle fits inside the case.
Here is a photo of the real part covered in a layer of soot on the outside. Easily cleaned off with alcohol and cue-tips.
The core is suspended inside the coil and is made of two parts. The inner part is threaded at both ends and is crimped onto the outer part.
Here I have changed the material of the outer part to clear, red plastic to make it clearer to see than two similar metal parts.