In general, there are 2 types of valves. The lowest priced and much more common is the pressure balancing valve. It balances the pressure from hot and cold so if someone flushes the toilet when you're showering, you don't get a blast of hot water. When the cold pressure drops from the flush, it instantly reduces the hot to match. With these, when you turn on the valve, you get full pressure from the start. You turn the valve to control the temp but not the pressure. It's full pressure or none.
The Thermostatic type is considerably more expensive. It allows you to control both temp and pressure.
