This is a typical balanced pressure proportioning set , the pressure of the system comes from the foam pump. Usually the outlet pressure of the foam pump is 0.1-0.2Mpa higher than the water supply pressure, and then the pressure of the foam concentrate is consistent with the water  before the balanced proportioner through the balance valve (can be built in or external).

Like the bladder pressure proportioning tank, the proportioning ratio will also change with the brand and variety of the foam, so strictly, the certification of this proportioner is only for a certain type of foam agent used for testing.
Balanced pressure proportioner are available in standard and wide flow types, and the wide flow type is usually used in foam-water sprinkler system.