Calibrate Differential Pressure Switch?

I know how to calibrate pressure switch, but how do I calibrate a differential pressure switch?

I have two pressure lines for seal water system.

Line 1: 3360 kPa
Line 2: 3460 kPa

I’m using the Make: UE controls, Type: J21K, Model: 357 differential pressure switch. Range: 0 - 4.8 Bar

I would like differential pressure switch to set/rest @ 275kPa/260kPa

What I did was calibrate the high side to set/reset at 275kPa/260kPa. I haven’t done anything to the low side.

When I installed this in the field connecting to two process lines, it actuated even though the difference of the pressure reading on the two gauges in respective lines were less than 275kPa .

The 5 way manifold was controlled to get the expected outcome but every attempted failed.

How do one calibrate a differential pressure switch?

Would appreciate your comments.

Thank you.

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Check these articles:


The J21K Differential Pressure Switch utilizes opposing metal bellows to detect pressure differences between two pressure sources. When the pressure at the high port exceeds the pressure at the low port by a pre-determined amount (set point), the mechanism operates a single snap-action electrical switch. Control set point may be adjusted by turning the internal adjustment hex screw

For set point adjustment and re-calibration, connect the “High” pressure port to a calibrated pressure source.

Set point adjustment is achieved by varying the gap between the mechanical actuator and the plunger on the electrical switch.

To raise the differential pressure setting, turn the 5/16" hex head screw left (clockwise).

To lower the differential pressure setting, turn the 5/16" hex head screw right (counter-clockwise).

Types with Optional Adjustable Deadband Switch (Option 1520)

J21K models with option code 1520 incorporate a snap switch with integral adjustment wheel. Turning this wheel raises or lowers the pressure rise set point. The fall set point remains constant.

To use the adjustable deadband switch:

  1. Determine set point and deadband values.

For example, a rising set point of 20 psid with a deadband value of 6 psid.

  1. Set the falling set point at desired deadband value (determined by subtracting the deadband value from the desired set point) using the standard adjustment screw as outlined above.

Using the example from step 1, 20 - 6 = 14, so you would set the fall set point at 14 psid. This is your constant.

  1. Set your deadband by turning the adjustment wheel left to raise or right to lower the set point.

Using the example from step 1, turn the wheel left or right until 20 psid is achieved. This is your set point.


Thank you Santhosh. Appreciate you help.

This really helps. I will try mechanically adjust the plunger online to achieve my expected state. Thank you.

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