I recently had a vacuum pump failure on the port engine and had a new pump fitted. The Piper Aztec F that I fly has a dual vacuum system. Prior to this the vacuum was always about 5 inches and the de-ice boots worked perfectly. The de-ice boots are relatively new, installed a couple of years ago, and are in very good condition. Since the new pump has been installed the vacuum is closer to 4 inches and when the deice boots are activated it rises to 5 inches. The boots don’t inflate now as a I found out on a flight yesterday back from Belgium when I entered light icing!
When the pump failed the plastic impeller shaft would have sheared and I wonder if some plastic parts have been shed into the system and are causing a blockage somewhere. I have attached a diagram of the system. If anyone has any idea about the cause of the failure of the de-ice boots to inflate, I would be grateful. I am going to take the plane to maintenance next week and it would be good to have some ideas beforehand. I watched them install the new pump and know that they didn’t check anything else in terms of a potential blockage due to shredded material.
Thanks for any help.
The plastic drive is outside the pump body so can’t get into the system, what it does is shear to protect the engine when the carbon vanes in the vac pump jam ( usualy because the vanes are worn out ).
The place I would start looking would be the actuating valve as it would seem that pressure is avalable.
I had exactly the same.
An expensive little venture.
I always avoid hot starts and make effort to ensure where possible.
One day despite double checking my spot, i was asked to move.
The failed hot start included one of those half backfires that kicks the prop half a turn the wrong way.(probably not helped by some ham-fisted input by me as I was still very new to the A/C)
Guess what next flight was without one Vac pump. The big one that runs the boots.
Once replaced the boots didn’t work.
Some debris was now downstream in the actuator/Valve assy.
Was a quick fix I believe, and an apology for not considering the possibility/likelyhood, and resolving before handing back. No charge.
I am quite lucky wirh our maintenance guys they are very fair.
Thanks A/C and Pete, gives me a good idea of where to ask them to look first.
GA Pete, I would not beat yourself up about the backfire and the Prop kicking back, vac pumps only fail when turned backwards it they are just about to die……… all you did was put it out of its misery a few hours early.
GA Pete, I would not beat yourself up about the backfire and the Prop kicking back, vac pumps only fail when turned backwards it they are just about to die……… all you did was put it out of its misery a few hours early.
That actually made me laugh out loud.
Thanks
Having been based for more than 10 years in a hangar where almost all planes had boots (TBMs, C4xx and above, etc) I got the impression that inop boots was a default evolutionary condition which required continuous human activity to disrupt 
Peter wrote:
Having been based for more than 10 years in a hangar where almost all planes had boots (TBMs, C4xx and above, etc) I got the impression that inop boots was a default evolutionary condition which required continuous human activity to disrupt
Not in my experience. Very reliable overall.
The comment from the Piper Forum was that it is probably debris or failure in the pressure control valve. I will find out next week when it goes in for maintenance.
In terms of reliability, this is the first time I have had any problem with the boots.
