• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Venturi Location (inst vacuum, not carb)

Seems to be the preferred spot.

If it doesn't work out, I have a larger one around here somewhere I'll give you. It should produce enough vacuum. KIMG0755.jpeg

Sent from my E6810 using Tapatalk
 

Attachments

  • KIMG0755.jpeg
    KIMG0755.jpeg
    45.1 KB · Views: 143
Well, I'm bummed. It think the venturi is fine because with a strong turn the needle jumps over. But when the strong turn is reduced to standard rate the needle settles on the doghouse momentarily, then drops to 1/3 or 1/2 of the correct deflection. Same when entering standard rate from straight and level gradually, the needle only moves a little. This gage has 7 years of being inop in the plane, after overhaul by Keystone. I'm thinking maybe its works (gimbals and such) might have vibrated in one position so long that they're compromised. Thoughts?
 
Hook up a vacuum cleaner to the exhaust end of the venturi. Then move the plane back and forth in the hangar.
 
Has this setup ever worked? It sounds like the venturi works fine. You get instrument operation in turns? Sounds like it's still 'shaded' by the cowl door. Try another style venturi or put a spacer under it to move it out closer to clean air.
Take a blower chuck and shop air and blow air into the venturi from about two feet away. If the instrument works, the venturi is wrong or located in a bad place.

Web
 
Thanks guys. I THINK the venturi is fine now, but the instrument is acting like it's "sticky". Good needle deflection in strong turns but "stuck" needle in gentle turns. I think I'll pull the instrument and the venturi out, and play around with vacuum cleaner wind by the bench. Any experience with instruments acting like this with known sufficient vacuum??
 
See my post 37 and yes it may have become compromised. Remove and inspect the instrument. If suspicious have it overhauled. That's assuming you now have the required vacuum displayed on that gauge and an assumed flow of air.

180* turn in 60 seconds once in the doghouse and coordinated. If not then I'd suspect the gyro rotation speed. Too late a 180 turn (>60 sec) or no doghouse = more vacuum. Too soon = less with flow needle.

FWIW there's adjustable ball bearing preload at both front and back of instrument the gyro cage is suspended on. Also bearings for the gyro. Plus a dampening pot and spring to smooth and adjust the gyro's precession. If any of that needs adjustment or gets compromised though wear and the instrument is noisy.......

Gary
 
wireweinie said:
Has this setup ever worked? It sounds like the venturi works fine. You get instrument operation in turns? Sounds like it's still 'shaded' by the cowl door. Try another style venturi or put a spacer under it to move it out closer to clean air.
Take a blower chuck and shop air and blow air into the venturi from about two feet away. If the instrument works, the venturi is wrong or located in a bad place.

Web
Click to expand...
Well, it didn't work at all with the venturi in the old location.

Now the needle swings to large deflection just fine, but seems sticky with small deflections.

I removed the venturi and connected the shop-vac to it on the downstream end, as Sky suggested, and I get 7" Hg static.

I've re-installed the venturi and plumbed it direct to the vacuum gage, i.e. instrument not connected. Tomorrow I'll fly that and see how much suction I get.

If that tests ok I'll remove the instrument (big pain, cuz it's in there with elastic stop nuts that are hard to reach), do all Gary's post #37 stuff, and test it with the venturi on the shop-vac. At least that will be definitive.
 
How much suction did you get during test flight with T&B attached to system?

If you can reach it just remove the screw-on air filter before the whole instrument. Then try again. Might just be the filter's constipated with dirt. If so disassemble and clean.

The needle can jump a bit until a steady coordinated 3*/sec turn is established then should settle into the doghouse.

Why not use NAS 487 grasshopper nuts for assembly?
 

Attachments

  • NAS_487-13_2.jpg
    NAS_487-13_2.jpg
    12 KB · Views: 317
BC12D-4-85 said:
How much suction did you get during test flight with T&B attached to system?

If you can reach it just remove the screw-on air filter before the whole instrument. Then try again. Might just be the filter's constipated with dirt. If so disassemble and clean.

The needle can jump a bit until a steady coordinated 3*/sec turn is established then should settle into the doghouse.

Why not use NAS 487 grasshopper nuts for assembly?
Click to expand...
I didn't have the suction gauge attached when test flying today. I figured if it worked well, then I'm done. And if it didn't - well, here I am.

Unfortunately I can't reach the filter. Can barely see it. The T&B is between other instruments, unfortunately. And unfortunately I was ignorant about grasshopper nuts until I'd already done the stop nuts. But that's what'll get used in the future, for sure!
 
Test flew today with the venturi connected only to the suction gage. It gives between two and three inches at 90 mph, and is rated for 2 inches. So I'm satisfied that the venturi location is now ok.

Removed the venturi and instrument, and connected the venturi to the shop vac with instrument and suction gage connected. Adjusted the suction to 2 inches. The instrument still seems to have a hitch in it, between zero and standard rate turn. Checked the filter, it's clean. Tested again with filter removed, same result. So I'm now pretty confident that the instrument has some sticky something or another in its innards. Go ahead, laugh at my Rube Goldberg arrangement. Take what ya got and make what ya want!:smile:

20181129_181327_HDR.jpg
 

Attachments

  • 20181129_181327_HDR.jpg
    20181129_181327_HDR.jpg
    68.4 KB · Views: 164
Hey looks like a good bench test! Does it hitch in both R and L rotation flat on the bench? I assume you laid it on a 360* polar plot and rotated at 3*/sec? (Joke). There's bearings that can flat spot from steady wear and a piston/cylinder damper that might need refreshing. If you have the curiosity have it examined and recertified then test again.

Or replace with another unit.

Gary
 
Hey Gordon, I've got a vacuum T&B decorating my hangar.
You're welcome to try it.
Good excuse for you to fly up there to Jefferson County for lunch or pie.
But I don't even remember where I got it, so who knows what kinda shape it might be in.
 
Just for the


Just for the h--- of it I looked at N3667N and the venturi is in line line with the cowl hinge on the left side. This PA12 still has all its original parts and no mods, so I would guess that was where Piper put it.
 
N86250 said:
Just for the h--- of it I looked at N3667N and the venturi is in line line with the cowl hinge on the left side. This PA12 still has all its original parts and no mods, so I would guess that was where Piper put it.
Click to expand...
That's where I relocated mine to, and it seems to be fine. Gives about 3+ inches of vacuum static.
 
You must log in or register to reply here.

Similar threads

Gordon Misch
Turn and Bank vacuum system
Replies
12
Views
8K
musket
musket
sekps
Venturi location?
Replies
5
Views
2K
sekps
sekps
T.J.
Cub venturi?
Replies
13
Views
8K
Clay Hammond
Clay Hammond
T
Lycoming bolted to a 95hp bootcowl
Replies
0
Views
992
tempdoug
T
Bearhawk Builder
Static Port Location
Replies
25
Views
4K
BC12D-4-85
BC12D-4-85
Back
Top