I have a shower that that loses pressure after a couple of minutes. All other fixtures in the house are fine, and I installed a new shower head thinking it may be clogged. I removed the stem and opened the water and have a strong continuose flow. I went to the local hardware supply and they told me to replace the valve stem, I did. It still does the same only now if you open the valve past 1-1/4 of a turn you lose pressure right away. I Have been adjusting the mix valve by turning it but don't know if I am doing it correctly. It is a Mixet set about 10 years old.