Deltadyne^® Differential pressure switches are used to indicate when the aircraft filter element is becoming blocked and needs to be changed.

Pall manufactures a series of mechanical and electrical indicators, with a range of connectors, qualified for aerospace use.

• Features
• Benefits
• How Does it Work

Features Visual 'Pop' Up button or Electrical Indication or both Range of pressure settings Thermal lock out device (optional) Benefits Advance warning of filter element blockage Thermal lock out device prevents false indication at cold start conditions Aerospace OEM approved

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How Does it Work?

Deltadyne^® differential pressure devices operate by sensing the differential pressure between ports upstream and downstream of the filter element. The differential pressure acts on a piston/magnet assembly that is contained in the indicator device.

Principle of Operation:

1. The differential pressure across the internal piston/magnet assembly reaches a preset value. This is determined by the range spring.
2. The piston (including magnet) moves downward. This reduces the attractive force between the magnet and the button/switch and therefore the button/switch actuates.
3. When the differential pressure reduces (i.e. a clean element is installed), the piston returns to its original position.
4. The button/switch is now re-set and is ready for use again.

Thermal Lock-Out

In some systems, operation at low temperatures can cause a false indication of a blocked element. To prevent this, an optional thermal lock-out device can be provided. At the stated temperature (e.g. below 32 °F, 0 °C), a bimetallic strip, mounted adjacent to the indicator button, curves inwardly sufficiently to prevent the button from rising. The same feature can also be programmed electronically.

Reed Switch or Microswitch?

A microswitch is typically used for high current applications and a reed switch is typically used for low current applications. The reed switch is hermetically sealed from the atmosphere and this protects the electrical contacts from oxidation.