Best Practices for Hydronic Systems Part 9: Three Valves Every Centrifugal Pump Needs
/
All centrifugal pumps in HVAC applications should be equipped with a shut-off valve, check valve, and a balance valve. Or, as an alternative, you can choose a valve that combines all this same functionality in one valve body.
Shut-off Valve. A shut-off valve allows you to isolate the pump for maintenance. It also lets you measure the pump’s shut-off head at start-up to verify that the head corresponds with what is published on the pump curve. This is a required pump start-up procedure per the 2019 ASHRAE HVAC Applications Handbook, as it ensures that the pump performs as designed.
Check Valve. A check valve should be installed on the pump discharge to prevent water flowing backward through the pump when the pump is not operating. This valve should be a center-guided, non-slam weighted design to prevent chatter and protect the pump from water hammer. When the pump stops, an inner, spring-loaded coil quietly forces the valve disc into the seat, shutting off backflow from the discharge of the pump.
Balance Valves. Balance valves are required to achieve a proportionally balanced system according ASHRAE 90.1 energy codes. They help ensure correct flow throughout the system. To proportionally balance the system you should install a balance valve on the discharge of the pump. This will facilitate the removal of excess pressure in the system in case the pumps are oversized (which they usually are).
The instructions for proportional balance can be found in Chapter 39 of the 2019 ASHRAE HVAC Handbook. During this procedure the balance valve is used to adjust the total system flow equal the design flow at the pump discharge. The excessive pressure across the valve can then be calculated and then removed by either trimming the pump impeller or reducing the pump speed. Once these adjustments have been made to the pump, the balance valve can be set to fully open to provide design flow. Just remember, not all balance valves are created equal in terms of pressure drop. Try to select a balance valve that has a low pressure drop when it is fully open. This will save a significant amount of energy over the life of the system.
Three Valves in One
If you want to save the owner money while keeping installation costs down, consider installing a valve that combines all of the above functionality into a single body. After all, it takes a lot less time to make two piping connections than six.
The B&G Triple Duty Valve is an all-in-one solution for shut-off, backflow prevention, and balancing. Designed specifically for hydronic HVAC systems, it has a low pressure drop for more efficient pumping. Just be sure to install the valve so that the stem points vertically and upward so the check will properly seat.
