Instrument Air Regulator Problems

[Stuart Robb]

I recently replaced an instrument air regulator (the one that lives on the pilots side firewall cunningly and totally encased in the wiring loom)as it ceased to work due to a small amount of corrosion around the valve.The symptom was that the pressure indicated on the instrument pressure gauge would climb with the air pressure increase when the de ice boots where activated. A new valve was purchased and fitted 15 flight hours ago and in the last 5 hours has started to do the same thing. The most probable cause is the new regulator is also faulty IE sticking closed and allowing the full delivery from the pressure pump to the instrument pressure line. Because it is in such an unpleasant spot to access I would like to know if we are over looking something simple before getting it out again and has anyone had a similiar experience?

[Richard Reeves]

The installation you describe sounds more or less the same as that in my B-55 Baron.  I had boots installed about 6 years ago, and had similar problems getting the instrument air pressure set properly.  As I understand it, essentially if a Baron has boots, the primary air system is a high pressure system that is set up to operate the boots.  The instrument air is provided by a take off that is in essence a pressure reducing valve located behind the lower sub panel of the interior on the pilot's side with low pressure plumbing to the instruments.

In my experience the problem you describe is likely the cause of that pressure reducing valve failing to function, which I would suspect is caused by:

- A defective valve;

- Excess pressure on the high pressure side interfering with the valve;

- Contamination in the high pressure system with particulates interfering with the pressure reduction valve.

I would have my shop replace the valve on a warranty basis (failing after 15 hours is ridiculous), check that all the high and low pressure settings for the boots and instrument air systems are properly set (i.e. at the pumps, the valves, etc.), and thoroughly flush the system (high and low pressure) to eliminate contamination.

The people at BF Goodrich in Akron, Ohio know this system inside and out.