I just bought my house and noticed there is a problem in the bathroom tub faucet and that is: the valve starts from the cold toward hot and as it goes toward the hot the water pressure increases and by the way the way it is made I do not have any access behind the wall to check how it is made. Is there any way I can fix this and have control over both water temperature's pressure?
Delta makes a line of shower valves (Monitor 17 series) that has separate Temperature and Volume controls in a single hole package. It approximates a thermostatic valve, which is a much more expensive valve.
The little arm at 2 o'clock is the temperature setting, and the larger one at 4 o'clock is the volume.
It would be necessary to replace both the valve body and the valve trim to use this solution.
I think what you are describing is normal. The valve starts off with cold water at low pressure, and as you move the handle, cold water pressure increases and it starts to mix hot in at low pressure. If it didn't behave this way then upon opening the slightest, you would get "full blast".