I have a single handle valve for the tub. I think it is made by Delta, but not 100% positive. It has a cartridge that sits on top of the valve. The water comes out as a dribble from both the shower head and spout. After some checking, the water pressure going to the valve is good and strong and after taking the cartridge off the valve the water pressure still is strong coming out of the valve. It's when the cartridge is on is when I have really no pressure. I have bought a new cartridge thinking it was in need of replacement. That didn't change. I opened up the cartridge and cleaned out some grim that was inside, but the same results. Any ideas what might be the problem? I'm not sure if there is a blockage in the valve or if it is ba. I have tried blowing the valve out, but that didn't seem to help.

When you cleaned the cartridge did you also check where it seats? Does your valve have seats and springs? Cheers, Tom

Well I got it figured it out. Between the time I posted this and reading the answer I took everything apart and blew out the lines and blew out a crumb size pice of bebris and that took care of my problem. Thanks for the help.