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How to bleed air from a Through-Hull Deployment Machine

01 February 2023

This article describes how to bleed air from our standard Through-Hull Deployment Machine.

This normally only needs to be done once, at the commissioning stage following installation.

Having a properly-bled system improves system performance. In some instances, bleeding the system is the cure for old, rarely-used machines.


  1. Start with the pole at the top position, with the locking pin in the gantry hole, as shown in the image above.
  2. Ensure the HPU tank is filled with hydraulic oil just above the Max level of its glass gauge.
  3. Disable the top sensor, so that the TOP light does not illuminate; see Note below.
  4. Press the UP button.
  5. Make sure the locking cylinder pin fully retracts.
  6. Hold the UP button for about 30 seconds.
  7. Release the UP button and immediately press the DOWN button (so that the pin does not have chance to retract until the pole is below the gantry hole).
  8. Release the DOWN button when the pole has been lowered below the hole.
  9. Enable the top sensor.
  10. Press the UP button until the flag reaches the sensor, and check that the pole automatically stops, and the pin extends into the hole.
  11. Top up the tank if required.
  12. Exercise the pole up and down a few times.
  13. Top up the tank to its maximum level with the pole at its top position.

Disabling the top sensor can be performed in a number of ways. Choose one of the following methods:

  • Bend the sensor flag outwards a small amount, so that it fails to activate the proximity sensor.
  • Remove one of the supporting bolts and loosen another, so that the sensor flag rotates downwards, thereby again failing to activate the proximity sensor.
  • Remove the wire from terminal 10 (from any side of the terminal block, whichever is easier) inside either the Local Control Unit or the Main Control Unit.


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