Category
DP Switch for Water Circuits
Monitor pumps, filters and flow in water circuits with the Beck 908 differential pressure switch.
A differential pressure switch for water confirms that water is flowing through a pump, chiller or strainer, or warns a strainer is blocking, with no power needed. The Beck 908 is adjustable from 40 to 200 mbar or 150 to 1,000 mbar, rated to 10 bar and -10 to +80 °C, with a diaphragm chosen to suit your medium.
1 Product · Differential Pressure Switch for Water
Selection guide
DP Switch for Water Circuits Guide
How a water differential pressure switch works
The switch senses the pressure drop across a component, such as a strainer or a pump, on a diaphragm. As long as water flows and generates that pressure difference, the contact stays in its running state. If flow stops, the differential collapses, the diaphragm returns and the contact changes over, typically interlocking the chiller compressor or heating boiler so it can't run dry or freeze without confirmed flow.
How to choose the Beck 908 for a water circuit
- Range: 40 to 200 mbar suits most flow-proving duties across a strainer or heat exchanger; 150 to 1,000 mbar suits a larger drop, such as across a pump.
- Diaphragm material: EPDM, NBR, FKM or silicone, chosen to match the water treatment chemicals or glycol content of your circuit.
- Connection: brass G 1/8, rated to a maximum operating pressure of 10 bar.
- Temperature: media from -10 to +80 °C, which covers chilled water, low-temperature hot water and most heating circuits.
- Setting: an adjusting screw sets the switch point on site against a reference gauge during commissioning.
For a continuous 4 to 20 mA reading instead of a switch contact, see the liquid DP transmitter. For air-side filter and fan switches, see HVAC differential pressure switches.
FAQ
Common questions
Why use a DP switch for chiller flow proving?
It confirms that water is actually flowing through the chiller evaporator before the compressor is allowed to start, protecting it from freezing or low-flow damage. A flow switch or pump run signal alone can't catch a closed valve or an air-locked pipe the way a differential pressure reading across the circuit can.
What range do I need for a strainer alarm?
40 to 200 mbar suits most strainer blockage alarms and general flow proving across chillers and heat exchangers. Choose 150 to 1,000 mbar if the strainer or component normally runs at a higher clean pressure drop, so the alarm point still sits comfortably mid-range.
How is the switch point set on the Beck 908?
With an adjusting screw, set against a pressure gauge or manometer reading during commissioning. Because it's field-adjustable, you can fine-tune the trip point to the actual clean and dirty pressure drop measured on your installed strainer or pump rather than a factory default.
Can the Beck 908 handle glycol or treated water?
Yes, when the diaphragm material matches the medium. EPDM and NBR suit most treated water and glycol mixes; FKM and silicone extend compatibility for harsher treatment chemicals. Tell us the glycol percentage or dosing chemical and we'll confirm the diaphragm.
Is this switch suitable for a heating boiler circuit as well as chilled water?
Yes. The Beck 908 covers media from -10 to +80 °C, which spans chilled water and low or medium temperature heating circuits, and confirms flow before a boiler or pump is allowed to run, the same interlock role it performs on a chiller.
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