Indicate when the aircraft filter element is becoming blocked and needs to be changed. Use as part of your diagnostics program.

• Aids with maintenance planning
• Advance warning of filter blockage
• Extensive range of indicators to choose from
• Compact and lightweight

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

Features

• Visual 'Pop' Up button or Electrical Indication or both
• Wide 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

How does an aerospace differential pressure indicator/switch 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. In a DPI, the red indicator warning button pops up. In a DPS, the switch moves to the open position.
   This indicates the filter element requires changing.
3. When the differential pressure reduces (i.e. a new element is installed), the piston returns to its original position.
4. The button/switch is 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 100°F, 37.8°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.