I just finished my first shower remodel and had a friend of a friend install the new shower valve that came with my American Standard faucet. After months of work I was finally able to use the shower last weekend and was disappointed to find that the pressure is much lower than prior to the remodel. I do have an old house (1930), but my pressure is quite good.
I've ruled out the new shower head as the culprit for the low pressure by testing it in the other shower, where it works great. Besides, the pressure is low coming out of the tub filler as well as the shower head. I've also noticed that when I turn on the water, then pull up the diverter on the tub filler, the shower head turns on, but a bit of water continues to run from the tub filler. Is this an indication of low pressure, or just a crappy tub filler? This never happened with my old fixtures, which were much cheaper. I also disassembled the valve and inspected it carefully. I found a small piece of solder, but removing that didn't seem to improve the flow.

The only thing that has really changed is the pressure balance valve. Could this be causing the low pressure? If so, how do I fix it, I really want my old water pressure back. Is it even possible to buy a non pressure balance valve? I don't have the flushing toilet temperature fluctuation problem that this valve is useful for, so I really don't need it in the first place.