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Air in Autopilot Hydraulic steering system
10-16-18, 04:40 AM (This post was last modified: 10-16-18 04:46 AM by Derek - Raymarine - Moderator.)
Post: #1
Air in Autopilot Hydraulic steering system
The first thing is to check the orientation of the pump, is it mounted on a flat, horizontal surface, such that the motor axis is horizontal? The three hydraulic pipes will either come out of the top of the pump valve block, or on some styles of pumps they will exit the end of the pump.
[Image: attachment.php?aid=2365], [Image: attachment.php?aid=2366]

In the first image you can see the pump mounted horizontally with the pipes exiting the pump from the top pf the pump valve block body.
In the second Image, you can see an alternative style pump with the pipes exiting the end of the body, note that the pump is still horizontal.

It is important that the pump is horizontal because this enables any air trapped inside the pump to naturally bleed away. if the pump axis is mounted vertically, the air will remain trapped, as well as the pump will damage the thrust bearings and gears.

Also note in the second picture a warning about NOT using thread tape to seal the threads of the pipe connectors. Thread tape should NEVER be used, since strands of tape can break loose and become trapped in the pump causing check valves to stick open or jam closed or damage to the pump rotors. Threads of the pipe connections should only be sealed with threadlock or similar thread sealing compounds.

Hydraulic oil when first put into a system will contain many microscopic air bubbles and these will gradually coalesce and form larger air bubbles which will interfere with the operation of the pump, hence the reason why it is important to mount it correctly to enable this air to bleed away to the hydraulic reservoir in the steering system.

There are three pipes connected to the hydraulic pump, two connect into the steering system and are used to drive the steering rams to port or starboard, the third pipe connects the pump to the steering system fluid reservoir. This reservoir needs to be higher than the pump since this encourages the air bubbles in the pump to naturally escape back to the reservoir.

The sign of air in the Autopilot pump is usually a high pitched screaming sound coming from the pump

The autopilot pump can often be more easily bled from air, following a new installation, as follows:

* Select AUTO and PRESS 3 -4 +10 course change buttons
* Manually turn the steering wheel steadily to PORT

By turning the wheel to PORT whilst the Autopilot pump is trying to turn to STARBOARD, the oil between the helm pump and the Autopilot pump is circulated between the two and so any air in the Autopilot pump is flushed straight back up to the Helm pump which is also usually the hydraulic fluid reservoir.

Make sure there is sufficient oil in the reservoir, otherwise more air will get sucked into the pump again!


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