How can you set a pressure in differencial pressure switch for defferencial pressure?

the pressure we set for the injector and tested on machine

The pressure in the tank will vary from your cutin pressure to your cutout pressure. If you increased the pressure in the system, your air-charge will now be wrong. A good rule of thumb is cutin - 2...

It can go into a tee in the plumbing or into one of the 1/4" taps on the tank tee if you have one. It really doesn't matter how you do it as long as the switch is close to the tank.

There is a couple of different options. Some washers are equipped with pressure adjustment knobs. Failing that...all come with either multiple spray nozzles or twist type vari-nozzles. For multiple...

100 psi