Now lets talk about the different types of valves. They consist of balancing valves, shutoff valves, flow metering valves, and automatic control valves.
Balancing valves are used at pumps, coils, chillers, and boilers to reduce the water flowing through them. When correct flow has been obtained the valve memory should be used or put a mark on the valve handle.
Shutoff valves are used on both the return and supply lines on a coil, pump, chiller, or boiler to isolate the equipment when fixing a leak or replacing it without having to drain the system.
Flow metering valves are sometimes used in place of the standard coil pressure drop balancing method due to there accuracy. However these valves should be installed properly or they will not be accurate. These valves require at least 5 and sometimes more straight pipe diameters on their inlet side and 2 to 5 straight pipe diameters downsteam in order to be accurate. Most metering valves will have an arrow on the side indicating direction of flow and should be checked by the TAB Technician.
A pressure gauge should be used on the entering and leaving side of the valve to get the valve differential. That reading is then used with manufactures curves, slide rules, or circular slide rules to obtain the GPM (gallons per minute) flow.
Automatic control valves are used with the control system to modulate the valve position depending on flow demand. Automatic control valves can be used for mixing or diverting flow with two or three inlets/outlets. These valves should be inspected closely for correct installation. I have provided diagrams of these valves to get a better idea of what they look like inside and how they work in a piping system:
