August 25, 2014

How does a differential pressure bypass valve work?

differential pressure bypass valve schematic

We get calls about selecting, applying and setting differential pressure bypass valves (DPBVs). Why, where and when are they needed, and how do they work?

The DPBV is a 2-way, self contained proportional valve with an integral differential pressure adjustment setting. The valve inlet is piped to the supply line and the outlet is piped to the return line. Caleffi's 519 Series prevents excessively high head pressure (a result of the branch piping 2-way zone valves closing) by allowing flow from the supply piping directly to the return piping. The 519 Series will open to start bypassing flow when differential pressure reaches the adjustment setting. Head pressure of a fixed speed pump will increase in proportion to the number of 2-way zone valves that are closed. DPBV's are not needed when using a pressure-controlled variable speed pump. Excessive differential pressure between supply and return lines is undesirable and can deadhead a pump, prevent zone valves from fully closing, cause circuit imbalance, and can result in corrosion, water noise and water hammer. A DPBV can be installed at the end of a zone valve piping circuit, or at the beginning, after the pump discharge.

Caleffi’s Technical Brochure 01007 explains more and describes how to adjust the DPBV set point.

Last modified: 
August 26, 2014
Balancing ValvesHydronic PrinciplesZone Valves and Radiator Valves
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