For this class (I would just name the class pressure instead of pressure_sensors) you need to look at the PressureSensors driver and the Pressures monitor f/w units. The monitor unit has an override for broadcast interval. FYI - this type of thing will be common in Leahi where we split f/w into two units: 1) low level driver and 2) higher level controller or monitor. So keep any eye out for this when matching functionality to what f/w is supporting.
It seems strange to add a magic number here, from a defined constant. I'd assume (guess) the relation between 300->225 is maintaining a delta P along the flow path (or across the membrane?), but it might be worth spelling out, at the top with the defines, or as a macro function of the input flow rate.
Not clear to me that this is any better than bypassing the dialyzer in previous state and is likely worse. The way you have it now, the dialysate being pushed by DPi is going to run into a stopped DPo and cause a big pressure spike and push dialysate into blood side.
