Ball valves, butterfly valves, and plug valves (seat valves) are the most common types of valves used in heating, ventilation, and air conditioning systems. Other common types of valves used in HVAC systems include knife gate valves, diaphragm valves, and gate valves. Hydronics-triple duty valves act as a check valve, shut-off valve, and balancing valve all at the same time. Automatic flow limiting valves are used to vary the speed of pumping systems that control the flow of the water in the domestic hot water pipe.