In my home, if the shower is running you will only get a trickle out of any other faucet. Pretty much, there is only enough pressure to run one thing at a time in this house. Where the city water supply comes into my home there is a pressure relief valve. Can I safley adjust this a little myself? Do I need some kind of guage to measure the psi to make sure I don't burst any pipes? Any advice is much appreciated.

First you need to measure your water pressure with a gauge and your water pressure should be 50 - 60 psi. Then determine if you have a pressure relief valve or a pressure reducing valve?

Next, post a new message and tell us what you have.

Also it sounds like you are having volume
problem in addition to the pressure.
An inspection of your water pipe at a "union" just may reveal lime and scale forming on the insides of your piping which may explain the problem of volume.
You will still need to do the pressure gauge test mentioned by another.

Check your water pressure before you do anything. This will tell you whether it is a pressure or a volume problem.
If this is in fact a pressure reducing valve, there should be a strainer somewhere prior to the device. Many PRVs have a strainer screen built into the device. I have seen a couple where the screen was completely clogged, stopping the water flow altogether.
Deb
The Pipewench

Can I get a gauge to measure the psi at Lowes? Anyway, I never thought of the volume issue. Thanks. How can I tell if it is a pressure relief or reducing valve? Here's a pic...

[www.renderosity.com]

Reducing valve

Hello,

That is a pressure reducing valve, and almost certainly the problem. It's got a little lime or calcium buildup on the union below. There is a strainer (as Deb mentioned) that can be cleaned, and the valve can be adjusted, but PRVs are a high-mortality item, and it may need to be replaced.

Lowe's may have a pressure gauge. It would attach to a hose bibb, shouldn't cost too much.

BTW, that wall looks like it could use a french drain behind it.

-Steve G