Adjusting the vacuum suction

[FredG]

Hi to all,

Are there any illustrated doc or video or discussion thread explaining how to adjust the vacuum suction? I believe through the regulator?

mine is indicating too high on the warning messages.

it's a 1989 M20J model.

your input will be greatly appreciated.

thx.

[EricJ]

The vacuum manifold is usually under the glareshield on the pilot side.   The regulator is essentially regulating a leak, and it's pretty easy to adjust.   The SMM section 37 covers the vacuum system and tells how to adjust the regulator.    In a pinch you can use the panel gauge to adjust it if it is way out of whack, just make sure the gauge is reasonably correct (and not the actual problem).

The locking tabs keep the adjustment from moving.   Bend the tabs back, adjust it as needed, and bend the appropriate tabs back up to lock it again.    This is what it looks like:

[PT20J]

As always with any adjustment, it's a good idea to determine that the gauge installed in the airplane is accurate by comparing it with a known good gauge before adjusting things. Vacuum regulators don't generally need periodic adjustment, so I might do some investigation, especially if the high vacuum indication is new.

[A64Pilot]

I’ve never seen one go high, just low as the pump wears. I’d trouble shoot it before I just adjusted it.

My guess is the leak is plugged, how long has it been since the filter was changed? Filters fall apart when they get old.

Back when people smoked the system would get nasty.

[FredG]

Thank you for your replies.

I wonder if the high vacuum could be also because I got a G5 to replace the HSI? Less equipment to share the vacuum with? The Artificial Horizon being alone to take the full vacuum?

 

[FredG]

13 hours ago, EricJ said:

The vacuum manifold is usually under the glareshield on the pilot side.   The regulator is essentially regulating a leak, and it's pretty easy to adjust.   The SMM section 37 covers the vacuum system and tells how to adjust the regulator.    In a pinch you can use the panel gauge to adjust it if it is way out of whack, just make sure the gauge is reasonably correct (and not the actual problem).

The locking tabs keep the adjustment from moving.   Bend the tabs back, adjust it as needed, and bend the appropriate tabs back up to lock it again.    This is what it looks like:

Hi Eric,

the SMM describes just this:

What is the "Bending tab" in your picture and which screw is to be turned?

Thanks for your help.

[N201MKTurbo]

The shaft with the roll pin is what you want to turn. Just push the tabs down with a screwdriver. Then rotate the shaft with your fingers till the vacuum is where you need it and then bend some tabs back up to hold it in place.

I have found if you adjust the vacuum to the bottom of the green arc, your gyros last longer.

 

And removing a gyro can make your vacuum high.

[EricJ]

6 hours ago, FredG said:

Thank you for your replies.

I wonder if the high vacuum could be also because I got a G5 to replace the HSI? Less equipment to share the vacuum with? The Artificial Horizon being alone to take the full vacuum?

 

Yes, I had to adjust mine when I did the same thing.   I've since replaced the AI with a 2nd G5 and deleted the vacuum system altogether (which is why I can takes pics of the manifold on the carpet).   

[FredG]

I have to say I couldn't find the regulator behind all the wires etc.

does it have to be opened up somehow to be reached?

thnks for your help

Fred.

[PT20J]

3 minutes ago, FredG said:

I have to say I couldn't find the regulator behind all the wires etc.

does it have to be opened up somehow to be reached?

thnks for your help

Fred.

It should be tight against the firewall, probably a little left of center accessed from the pilot’s foot well.  It shouldn’t be too buried because the largest part is the garter filter which needs periodic replacement. 

[FredG]

33 minutes ago, PT20J said:

It should be tight against the firewall, probably a little left of center accessed from the pilot’s foot well.  It shouldn’t be too buried because the largest part is the garter filter which needs periodic replacement. 

Thank you, I will try again tomorrow.

[FredG]

Hi folks,

Just to let you know that I have successfully located the regulator and adjusted the vacuum down. It's a contortionist exercise to reach and it's with finger tips!

I suspect that in a proper adjustment, many of the wiring could be disconnected to give a better access, and most definitely required during the filter change.

Thanks for your help.

F.