Pressure Reducing Valve troubleshooting

I could post this on a plumbing forum, but you guys are much better at explaining why things happen, not just how to fix it. So here’s my problem.

I have leaks all over the house. Shutoff valves aren’t working. There’s evidence of corrosion on all the copper pipes. My water gauge, hooked up to the laundry faucet, reads 90 PSI.

So I figure my valve is set too high. I spin the adjusting screw counterclockwise on the PRV, and still the gauge reads 90. I spin the screw until I think it’s waaaaay too much, and it still says 90.

So I run a faucet. It comes out at a good pressure and then drops off to a dribble. “Good,” I think, “the valve is doing its job and reducing the pressure. I’ve turned it too low and just have to find the sweet spot.”

'cept that doesn’t work. Even if I leave it at low pressure, within 30 seconds of shutting off all faucets, the gauge is back up to 90 PSI. Why?! Why does it return to this very-high pressure? Why isn’t the valve keeping the pressure low? Is the valve failing, and if so, in what manner?

The valve diaphragm or seat is corroded and isn’t sealing properly, or it has a pinhole leak in it.
Replace it.

That’s how I ended up with my first child. ::ba dum csh::

Can I just replace the diaphragm, or is it just simpler/easier/cheaper to replace the whole PRV?

They are not expensive. If you can DIY then I doubt it would cost you much over $50.

Sounds more like a flow restrictor than a pressure regulator. Why are you restricting pressure in the first place? Are you on a well with a pressure switch and tank or a public supply? I’d replace it to verify it was the regulator. Pricing can’t be all that much. I wouldn’t take it apart to repair it. In industry, we never do as there is never a guarantee that the settings are correct afterwards. BTW, this won’t fix the leaks all over the house from corroded copper pipes and fittings. Your piping should be able to handle 90PSI (~6Bar)

90 PSI isn’t a problem. Its only slightly more than the average provided in this state.

A pressure regulator with a pinhole leak is functioning, except at very low flow. From zero to tiny flow, the pressure is high. At tiny flow, it reduces pressure, At the set pressure, it unrestricted flow. Was it put on to reduce pipe hammer ?

There might have been poor solder used ? Or is the hammer excessive ?
Not sure you need to repair the pressure regulator, … its there to prevent damage. You need to repair the pipes AND then prevent damage. Why not repair the pipes so that they are good when used at the ordinary pressure of 90 PSI/ 60 metres.

But 99% of the day is spent with no flow, isn’t it? Wouldn’t that put a lot of pressure on my fittings?

So in the SDMB’s opinion, is 90-100 PSI fine, and the problem is my shutoff valves are old and need replacing? Cuz that’s a lot easier to fix, considering the positioning of the PRV.