Something flaky here (Airborne 133A4 vac reg)

[HRM]

This is a closeup of the Airborne 133A4 vacuum regulator in my E. The arrow points to what I presume is a locking-nut that must be loosened in order to adjust the regulator with the knurled knob on top. Isn't that nut supposed to have a piece of security wire on it?

[cliffy]

Is there a hole drilled in the "nut" for safety wire to go through?

The bracket its bolted to looks a little "roughly" made also.  

[N201MKTurbo]

I've seen two kinds. One with the jam nut like yours and one that has a roll pin stuck in the shaft and a bunch of little fingers that you bend up around the roll pin to keep it in place. It seems like tightening the jam nut is sufficient. lock wire seems redundant.

I looked on line and could not find a service manual for the valve, but there are images online with and without a lock wire hole. So did they remove it because it was redundant or add it because they were moving???

It never hurts to lock wire it. So drill a hole for the wire and wire it so you can sleep at night.

Edited March 14, 2017 by N201MKTurbo

[cnoe]

There's wire on this one (as seen on TV).

 

[HRM]

15 hours ago, cnoe said:

There's wire on this one (as seen on TV).

 

This is similar to another picture I saw. I have as yet to pull the cowl and look at mine. 

[HRM]

16 hours ago, N201MKTurbo said:

I've seen two kinds. One with the jam nut like yours and one that has a roll pin stuck in the shaft and a bunch of little fingers that you bend up around the roll pin to keep it in place. It seems like tightening the jam nut is sufficient. lock wire seems redundant.

I looked on line and could not find a service manual for the valve, but there are images online with and without a lock wire hole. So did they remove it because it was redundant or add it because they were moving???

Here's a synopsis. I think the reg was originally behind the panel and was moved out to the engine side at some point. It may have been when the Aerotech filter, which is on the other side of the bracket, was installed.

I have as yet to pull the cowl and look at mine, but I am guessing that the jam nut (thanks for the terminology!) has a lock wire hole and it will have a lock wire soon.

Is the adjustment process just to loosen the jam nut and turn the knurled shaft? Are there detents or does it just turn freely?

[cnoe]

43 minutes ago, HRM said:

Are there detents or does it just turn freely?

I doubt there are detents; there are not on the newer style.

Typically turning clockwise will increase spring pressure thereby raising the vacuum reading.

[N201MKTurbo]

I'm not sure it is actually a regulator. It might be an adjustable leak. If your vacuum is low I would make sure you don't have any leaks.

I usually adjust mine on the low side of the green. It seems to make my gyros last longer.

yes, loosen the nut and adjust the little knob. It is not very sensitive, it takes a turn or two make a difference.

[HRM]

7 hours ago, N201MKTurbo said:

I'm not sure it is actually a regulator. It might be an adjustable leak. If your vacuum is low I would make sure you don't have any leaks.

I usually adjust mine on the low side of the green. It seems to make my gyros last longer.

yes, loosen the nut and adjust the little knob. It is not very sensitive, it takes a turn or two make a difference.

OK, if truth be told, my vacuum is high. Not always, but enough to drive me crazy with my engine monitor. Anytime vacuum gets above 5.5 the red alarm comes on. 

The alarm used to come on a lot on the low end, but after the new pump it's the other way. The new pump went in at annual and I feel confident no adjustment to the regulator was made. I do think, given all the scratches and wear on the jam nut and knob, there were adjustments made over the years to accommodate various things. My E is a vacuum hog--instruments, 3-axis AP and the retractable step. 

I called my IA (who installed the pump at annual) and he said to back it off a quarter turn and see if that ended the nuisance alarms. 

Below is a graph of RPM vs Vac from a flight I made today (no time to adjust the knob). I am wondering if the regulator has gone south. Looks like it has trouble on high RPM moves:

[carusoam]

Harley,

Doesn't look like it is regulating at all.  It is a direct relation with the engine rpm according to the graph...

Have your mechanic make it work or get a new one...

Best regards,

-a-

Edited March 16, 2017 by carusoam

[HRM]

21 hours ago, carusoam said:

Harley,

Doesn't look like it is regulating at all.  It is a direct relation with the engine rpm according to the graph...

Have your mechanic make it work or get a new one...

Best regards,

-a-

Yes, this has mystified me. It should follow RPM, just not go above the maximum (5.5).