Double Regulating Valves or balancing valves is a valve commonly found in water and HVAC systems. Double regulating valves are used to regulate flow by rotating hand wheel and also combines flow measurement in one valve. Typically DRVs are used to control water temperatures.
Double regulating valves are pressure independent yet pressure sensitive and they react to pressure changes from the water flowing into them. It causes the valve to either open or closes, thus maintains a pressure balance. Balancing this pressure between the two hot and cold water supplies keeps the temperature consistent. For example when a toilet is flushed, it doesn’t cause a sudden drop in cold water supply to a shower.
The handwheel can be used to shut off the flow.