You may also have only 50 psi of water pressure going into the regulator. If you set it above 50 and only have 50 going in, you won't get more pressure going out.
If you set it below 50 (say to 40 psi) and have already pressurized the gauge on a closed system to 50 psi, you will have to leak some of the water out of the closed system to let the pressure come down to the new pressure (as in the example 40 psi).
2012 GMC 3500 Duramax Crew Cab, SuperGlide 20k
2014 Cedar Creek 36B4, LP Onan, Level-Up, Trail-Air pin, electric fridge