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Suction Gage no suck any more

thomas1142

By thomas1142
in Modern Mooney Discussion

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thomas1142 Proficient

thomas1142

Posted
Posted

Went out to fly today on such a beautiful day. Once I started the engine I noticed the suction gage  was not registering. During the runup it was all over the place. I did not see any lights on the annunciator panel, nor did any instrument seem impacted. 

I'm assuming its the gage, right? If so is the gage hard to change out?

 

steingar Grand Master

steingar

Posted
Posted

The fact that I will soon be staking my life on a little machine that is best known for breaking at the most inopportune time does not fill me with quiet confidence.

My best guess for the OP is a leak in the system somewhere. Not unthinkable, seeing how those hoses could date back to an era of big hair, shoulder pads, and Molly Ringwald.

  • Haha 1
carusoam Grand Master

carusoam

Posted
Posted

Did you test the annunciator to know the lo vac light comes on?

Some annunciatiors need to be tested each flight to have their lo fuel lights activated...

Best regards,

-a-

LANCECASPER Grand Master

LANCECASPER

Posted
Posted
4 minutes ago, thinwing said:

Pump

I vote for the pump also. You have a late model J. Do you have standby vacuum? If it's clutch driven bring itdown the rpm to 1000 and turn it on. If it's electric standby just turn on the master and turn it on without the engine running and see what happens to the gauge.

thomas1142 Proficient

thomas1142

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Posted
1 hour ago, carusoam said:

Did you test the annunciator to know the lo vac light comes on?

Some annunciatiors need to be tested each flight to have their lo fuel lights activated...

Best regards,

-a-

I check the lights at every flight, all looked good.

  • Like 1
thomas1142 Proficient

thomas1142

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Posted

The main pump is less than 50 hrs old, it was replaced at the last annual in February of this year. 

I always test the back up pump during the run up. No change to the reading on the guage.

LANCECASPER Grand Master

LANCECASPER

Posted
Posted
1 hour ago, steingar said:

The fact that I will soon be staking my life on a little machine that is best known for breaking at the most inopportune time does not fill me with quiet confidence.

I got my instrument rating in '95 and flew IFR for a year without a backup pump or back up attitude indicator. Then in '96 I bought a Mooney that had standby vacuum, better, but still no backup attitude indicator. Since 2000 I haven't flown an airplane without a backup attitude that gets it's power from another source. I wouldn't consider IFR without a backup attitude indicator. In theory you can stay right side up with the turn coordinator, but under the stress a lot of people don't do so well.

  • Like 2
LANCECASPER Grand Master

LANCECASPER

Posted
Posted
1 minute ago, thomas1142 said:

The main pump is less than 50 hrs old, it was replaced at the last annual in February of this year. 

I always test the back up pump during the run up. No change to the reading on the guage.

Is the backup clutch driven off of the engine or is it an electrically driven pump that's in the tail?

LANCECASPER Grand Master

LANCECASPER

Posted
Posted
On 10/30/2018 at 9:47 PM, thomas1142 said:

Electrical, in back tail

Ok if the gauge is doing the same it may be the regulating valve since you're getting the same reading with both pumps. The switch that triggers Hi or Lo Vac may not be working.

I just took out the vacuum system in my Mooney and the regulator and switch sold this past week.

switch:

 

regulating valve:

 

carusoam Grand Master

carusoam

Posted
Posted

See if you can capture a video of its behavior...

It will shorten the mechanics time of starting the engine to verify what you are describing...

Also, test the electric pump on the ground with the engine off...

If the vac comes on nice and steady like usual... this is a sign that the mechanical pump is mis-behaving...

My procedures are to test separately in this way... really let’s you know the electric one is capable...

Let me know if I missed something.  PP thoughts only...

Best regards,

-a-

  • Like 1
steingar Grand Master

steingar

Posted
Posted
10 hours ago, LANCECASPER said:

I got my instrument rating in '95 and flew IFR for a year without a backup pump or back up attitude indicator. Then in '96 I bought a Mooney that had standby vacuum, better, but still no backup attitude indicator. Since 2000 I haven't flown an airplane without a backup attitude that gets it's power from another source. I wouldn't consider IFR without a backup attitude indicator. In theory you can stay right side up with the turn coordinator, but under the stress a lot of people don't do so well.

I've been thinking about this, and I'll bet the AI in the iPad will do in a pinch.  I will certainly find out during my training.

Bravoman Mentor

Bravoman

Posted
Posted
17 hours ago, LANCECASPER said:

I got my instrument rating in '95 and flew IFR for a year without a backup pump or back up attitude indicator. Then in '96 I bought a Mooney that had standby vacuum, better, but still no backup attitude indicator. Since 2000 I haven't flown an airplane without a backup attitude that gets it's power from another source. I wouldn't consider IFR without a backup attitude indicator. In theory you can stay right side up with the turn coordinator, but under the stress a lot of people don't do so well.

I totally agree about not flying instruments without the redundancy you describe. As to  being able to pull it off in the clag without an attitude indicator, I think that unless you train religiously on partial panel, it’s not going to end so well.

  • Like 1
thomas1142 Proficient

thomas1142

Posted
  • Author
Posted

Pulled glare shield, looked under the panel and all seemed good. Maintenance took a look at it and checked it all out, even removed the vacuum pump to make sure nothing funny was going on. All checked out, gauge is the issue. Anyone got a spare?

Yetti Grand Master

Yetti

Posted
Posted
On 10/31/2018 at 7:58 AM, Freemasm said:

The gage and status lgts should not contradict. If you want to verify the vacuum gauge cal, switch pressure setting, status light system (not just lamp) operation, there's a very cheap way. Make a water manometer out of tygon (clear vinyl) hose and a 2x4x8. A drop of food coloring will help make the water more visible.  

1 inch of Hg = 13.4 inches water. 

 

Also useful for balancing BMW throttle bodies. Or outboard engine carbs.  Clear plastic tubing, a yard stick, and ty wraps will have you going.  Some people use Automatic Transmission Fluid in the tubing.   It moves more slowly than water and if you suck it into some things it is better than sucking water into things.

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