The Gtech effort is a brilliant example of what "Men in Sheds" can do.
We would probably call it an "automatic bag squeezer". Note that it pushes out a fixed volume. It may be easy to modify the design to offer an adjustable volume. It looks very similar to the one described here
Needless to say, it lacks many of the refinements required by the MHRA RMVS.
Meanwhile, does anyone know how Government plans for the Rapidly Manufactured Ventilator System are progressing ... have they issued the UOR* yet?
* Urgent Operational Requirement