shower water pressure

While unwinterizing our pod I noticed that the shower valve has an anti-siphon feature (this stuff is new to us as we got our pod last fall and managed only 1 trip before the snow came to the Sierra).  If you disconnect the shower hose at the valve you can see what kind of water flow you have there.  Could be the valve is blocked by scale from the hot water heater.  There is just a little hole on the top of the valve where the hose connects for the water to go through and the scale chunks I cleaned out of our tank when I put in the new anode rod could easily stop it up.  Also, since the anti-siphon valve drains the shower hose, you could have an entomology experiment in it that has blocked the hose.