need replacement vacuum actuator for 1990 vintage precise flight speed brakes

[steve wilbur]

Does anyone know of a fix for a torn rubber diaphragm in the Brittain Industries vacuum actuator used in the vacuum operated precise flight speed brakes.  The rest of the system is in good shape and it seems like overkill to upgrade it to the electric version for lack of a simple rubber diaphragm.  Has anyone done the upgrade?  If so, was it worth the money?

[kortopates]

that’s the one part that isn’t available. many have done the upgrade.


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[Aerodon]

Steve, now that you have the servo out, you can see if the part number matches the Brittain autopilot servos.  Can you post another picture to show whether it has a 'chain'  or fitting on the pulling side?

 

 

Aerodon

[steve wilbur]

Hi Aerodon, thanks.  Doesn't look like the part number matches the Brittain autopilot servos.  Here is a picture of the pulling side.  The connection to it is still in the plane, so I'm not sure what it looks like.

[Guest]

Maybe an application for the electric step actuator conversion?

Clarence

[carusoam]

4 hours ago, M20Doc said:

Maybe an application for the electric step actuator conversion?

Clarence

Let me invite @takair to stop by…

-a-

[takair]

11 hours ago, M20Doc said:

Maybe an application for the electric step actuator conversion?

Clarence

Good thought, but I don’t think the speed of my current actuator is fast enough. The faster version likely would not have enough torque. From there, the actuators get rather heavy. Do you know if the system was a TC option or STC?  I had looked at the STC version previously and I think it is difficult to put an STC on top of someone else’s STC. To be honest, after I ran the numbers, the existing electric conversion seemed like a relatively good deal. 

[see_kay]

On 3/22/2022 at 5:02 AM, steve wilbur said:

Hi Aerodon, thanks.  Doesn't look like the part number matches the Brittain autopilot servos.  Here is a picture of the pulling side.  The connection to it is still in the plane, so I'm not sure what it looks like.

Did you find a solution?

My M20K speed brakes just failed, I suspect a similar problem, vac pump is good and solenoid is operating but no movement from the brakes.

If you still have your actuator - would you mind measuring the diameter of the bellows/cylinder and letting me know?

I have an idea about how to resurrect it.

Thanks

Chris

[takair]

I think, but not 100% sure, that the same BI 706 is used in the original retractable step.  We sell many electric replacements for those who want to remove the vacuum system.  The removed vacuum step actuators then pop up for sale…..so you might search for one of those.  

[see_kay]

13 hours ago, takair said:

I think, but not 100% sure, that the same BI 706 is used in the original retractable step.  We sell many electric replacements for those who want to remove the vacuum system.  The removed vacuum step actuators then pop up for sale…..so you might search for one of those.  

Thanks Rob

Very useful lead

[0TreeLemur]

I have read on these pages that there is a company called Belofram who makes parts for diaphragms for pneumatic actuators.  I've also read that if you contact them with the correct information in terms of fold type and dimensions, they will sell you one to fix a piece of industrial or farm equipment.  If you search MS for this topic you might find someone who knows more about it than I do.  I kind of lost interest once I figured out how to patch the step actuator diaphragm on our previous C model and didn't follow up on it any more.   I think that some have had luck with them, without using the word "airplane".

[kortopates]

On 8/26/2023 at 1:13 AM, see_kay said:

Did you find a solution?

My M20K speed brakes just failed, I suspect a similar problem, vac pump is good and solenoid is operating but no movement from the brakes.

If you still have your actuator - would you mind measuring the diameter of the bellows/cylinder and letting me know?

I have an idea about how to resurrect it.

Thanks

Chris

Don't be quick to assume that actuator is the problem. The conduit that carries the cable is much more likely to fall apart before the bellows. If yours haven't been replaced yet, I can't imagine how they could be still be fully functional. They fall apart with age. You have to drop the belly pan to see everything, but you merely need to get under the gear to check the integrity of the conduit and cables.

[Fly Boomer]

3 hours ago, kortopates said:

you merely need to get under the gear to check the integrity of the conduit and cables.

And if, as you suspect, they are bad, what's the cure?  Those who have contacted PreciseFlight have reported "no help available".  I know you can remove the old system and buy new, but apparently it's not a drop-in replacement, and not cheap.

[kortopates]

They were still selling conduit and cable pretty recently, so i expect they still do. Getting it from them will be a big time saver but i am sure the materials can be sourced elsewhere much easier than the actuator boot.
My boot is older than yours but still in great condition.


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[Igor_U]

On 3/12/2022 at 2:39 PM, steve wilbur said:

Does anyone know of a fix for a torn rubber diaphragm in the Brittain Industries vacuum actuator used in the vacuum operated precise flight speed brakes.  The rest of the system is in good shape and it seems like overkill to upgrade it to the electric version for lack of a simple rubber diaphragm.  Has anyone done the upgrade?  If so, was it worth the money?

 

Steve,

Bellofram makes rolling diaphragms in different sizes and you can get their PDF manual with link below. 

I know they have smaller ones for the wing servo but this one is looking bigger, almost as big as the servo for retractable step.

https://www.belloframdiaphragm.com/assets/documents/brd-design-manual.pdf?updated=1559828098

Have a look in the manual if your size is available or give them a call. I spoke to them years ago but never needed the parts as my servos are still in the good condition.

 

Good luck

[see_kay]

On 8/27/2023 at 1:34 PM, see_kay said:

Thanks Rob

Very useful lead

I received a $14,000 repair quote to install a new electric speed-brake system – an ‘upgrade’ that did exactly the same as the original vacuum operated unit.

I assumed that the diaphragm was the problem, but I couldn't locate a replacement to repair my existing unit - at least one that was still intact - so decided to experiment.

Having checked that the Vac pump and actuator solenoid were functional, I removed the RH rear seat panel and the belly plate and was able to remove the vacuum actuator. Sure enough there was a tear in the rubber.

I used motor cycle inner tube 4.00/4.50 19" (normal weight) and cut a sleeve from it a little longer than the original diaphragm..

The sleeve can be pulled over the inner cylinder - approx 4" diameter - and then (with some difficulty) stretched over the end lip of the outer cylinder. Here it is secured with a hose clamp.

The other end of the sleeve should be trimmed neatly and clamped under the end-plate of the inner cylinder.

Bench tested ok, re-installed with slightly stronger retraction spring (the tube rubber is thicker than the original diaphragm)

All working again - I will keep you posted if any problems appear...

[Igor_U]

@see_kay

It would be great if you'd post some pictures... 

[see_kay]

On 9/30/2023 at 4:00 PM, see_kay said:

I received a $14,000 repair quote to install a new electric speed-brake system – an ‘upgrade’ that did exactly the same as the original vacuum operated unit.

I assumed that the diaphragm was the problem, but I couldn't locate a replacement to repair my existing unit - at least one that was still intact - so decided to experiment.

Having checked that the Vac pump and actuator solenoid were functional, I removed the RH rear seat panel and the belly plate and was able to remove the vacuum actuator. Sure enough there was a tear in the rubber.

I used motor cycle inner tube 4.00/4.50 19" (normal weight) and cut a sleeve from it a little longer than the original diaphragm..

The sleeve can be pulled over the inner cylinder - approx 4" diameter - and then (with some difficulty) stretched over the end lip of the outer cylinder. Here it is secured with a hose clamp.

The other end of the sleeve should be trimmed neatly and clamped under the end-plate of the inner cylinder.

Bench tested ok, re-installed with slightly stronger retraction spring (the tube rubber is thicker than the original diaphragm)

All working again - I will keep you posted if any problems appear...

Here are a few pics.

Damaged diaphragm with small tear

Repaired, showing hose clamp

End plate showing clamping bolt/cable and spring attachment point