The ornamental design for a pressureregulator and piston, as shown and described.
FIG. 1 is a top perspective view of a pressure regulator and piston according to the invention;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is a side view thereof;
FIG. 6 is a top view thereof;
FIG. 7. is a bottom view thereof; and,
FIG. 8 is a bottom perspective view thereof.
In the drawings, the dash/dot/dot/dash broken lines depict claim boundaries and form no part of the claim; the evenly spaced broken lines illustrate portions of the article that form no part of the claimed design.