Andair duplex fuel pump knob plastic wear

[CJT]

Has anyone experienced this kind of wear?
It’s made changing fuel tanks impossible
Aircraft spruce doesn’t sell it as spare, advised to buy new valve
Waiting endlessly for reply from Andair UK

Any remedy?

 

[lr172]

That looks like someone forced it on in the wrong position to me. should be no wear on that pin if installed properly.

 

[IO390]

I contacted Andair since they are local to me. They said those pins are a close fit so it's tricky to remove them, the options you have are to machine out the pin and replace but this is difficult as it's a precision part. Alternatively they can ship you a replacement knob which shouldn't be expensive. I have DMed you with a contact email.

 

[AZSteve053]

Is there ANY chance this is related to the dual SDS fuel pump failure posted by same OP ? FOD getting into fuel valve makes it difficult to move from L to R or to OFF - excessive pressure causes wear on knob attach, chips inside valve from FOD being chopped up then proceeds to fuel pump causing failures... Just a thought.

 

[dmattmul]

Has anyone experienced this kind of wear?
It’s made changing fuel tanks impossible
Aircraft spruce doesn’t sell it as spare, advised to buy new valve
Waiting endlessly for reply from Andair UK

Any remedy?View attachment 115675

They can have it to you in 10 days max, I've ordered many parts direct over the years and arrives very soon. BTW they don't do e-mails well at all, if needed call in the morning their time.

 

[N10KE]

Is there ANY chance this is related to the dual SDS fuel pump failure posted by same OP ? FOD getting into fuel valve makes it difficult to move from L to R or to OFF - excessive pressure causes wear on knob attach, chips inside valve from FOD being chopped up then proceeds to fuel pump causing failures... Just a thought.

Seems a bit too coincidental to me as well.

 

[CJT]

Is there ANY chance this is related to the dual SDS fuel pump failure posted by same OP ? FOD getting into fuel valve makes it difficult to move from L to R or to OFF - excessive pressure causes wear on knob attach, chips inside valve from FOD being chopped up then proceeds to fuel pump causing failures... Just a thought.

I don’t think the particles from here can enter fuel line

 

[CJT]

They can have it to you in 10 days max, I've ordered many parts direct over the years and arrives very soon. BTW they don't do e-mails well at all, if needed call in the morning their time.

View attachment 115698

Thanks

 

[CJT]

I contacted Andair since they are local to me. They said those pins are a close fit so it's tricky to remove them, the options you have are to machine out the pin and replace but this is difficult as it's a precision part. Alternatively they can ship you a replacement knob which shouldn't be expensive. I have DMed you with a contact email.

Thanks

 

[CJT]

That looks like someone forced it on in the wrong position to me. should be no wear on that pin if installed properly.

Every time I change fuel tanks position, I pull the knob and turn it, I think that is the way it is supposed to be used

 

[AZSteve053]

On MY Andair single path fuel control valve with metal handle - you can change tanks WITHOUT raising the knob. You only raise knob to SHUT OFF fuel.

 

[Toobuilder]

Every time I change fuel tanks position, I pull the knob and turn it, I think that is the way it is supposed to be used

On mine, the knob is only used to get the lever to the OFF position. If you lift the knob while going between tanks, you lose the benefit of the positive stop at the desired left or right position.

 

[dmattmul]

Every time I change fuel tanks position, I pull the knob and turn it, I think that is the way it is supposed to be used

Don't think so. You pull the knob to turn the fuel selector "OFF". Switching tanks is just done with a turn of your wrist. That way you can't accidently turn the valve off.

I've got a spare knob if you need to borrow it till your new one arrives. PM me if needed.

 

[dmattmul]

Has anyone experienced this kind of wear?
It’s made changing fuel tanks impossible
Aircraft spruce doesn’t sell it as spare, advised to buy new valve
Waiting endlessly for reply from Andair UK

Any remedy?View attachment 115675

I think after review of your knob operations (Don't pull the knob up to change tanks) you have found root cause. It's critical to get the knob exactly positioned so the suction side (3/8 in) gets perfectly aligned. As other have implied it too much of a coincidence. Our 3/8 in suction side tubing is marginally ok. Cirrus went to 1/2 in after a few years because who knows but I will speculate 3/8 in its marginal. Most likely (speculation) you did not have the knob in a "perfect" orientation, and you were getting suction side cavitation which destroyed your Walbro fuel pumps.

 

[lr172]

I think after review of your knob operations (Don't pull the knob up to change tanks) you have found root cause. It's critical to get the knob exactly positioned so the suction side (3/8 in) gets perfectly aligned. As other have implied it too much of a coincidence. Our 3/8 in suction side tubing is marginally ok. Cirrus went to 1/2 in after a few years because who knows but I will speculate 3/8 in its marginal. Most likely (speculation) you did not have the knob in a "perfect" orientation, and you were getting suction side cavitation which destroyed your Walbro fuel pumps.

The locking pin has nothing to do with this wear. That white round pins purpose is to lock and index the knob to the shaft. That pin is supposed to fill the gap from the flat machined in the shaft. I just don’t see how this got worn the way it appears in the pic unless someone jammed it own on the round part of the shaft instead of the flat. You can’t apply enough rotational force to shear it off, as the shaft has no resistance. The locking is done via a different pin riding in a slot in the body.

 

[dmattmul]

The locking pin has nothing to do with this wear. That white round pins purpose is to lock and index the knob to the shaft. That pin is supposed to fill the gap from the flat machined in the shaft. I just don’t see how this got worn the way it appears in the pic unless someone jammed it own on the round part of the shaft instead of the flat. You can’t apply enough rotational force to shear it off, as the shaft has no resistance. The locking is done via a different pin riding in a slot in the body.

Larry, my point was I don't believe he is getting the valve turned to the exact position to allow free flow of fuel to the pump. My theory is this is because the white pin is worn and difficult to "feel" the correct position when it is rotated. (Especially when top knob is pulled up) Possibly a clearer meaning of "It’s made changing fuel tanks impossible". I took that as the valve is difficult to rotate and possibly difficult to "feel" the correct position.

I can rotate my valve a few degrees (going from one tank to the other) and I can see a amp reduction (I have a Hall effect sensor on both my Walbro fuel pumps) and hear a slight different pitch the fluid passing through the orifices is making.

I don’t believe a failing fuel valve and 2 Walbro pumps failing very early is a coincidence. Just my opinion of course.

 

[Toobuilder]

Seems reasonable. If the lever is not indexed properly on the shaft, and the operator is not using the built in locating feature (because he’s lifting the knob to switch tanks), who knows where the valve ports are ending up? It’s possible they are out of alignment and partially obstructed in some phases of operation. This could theoretically cause low fuel flow through the pumps, cavitation and excessive heat.

Is it possible the "wear" on the indexing pin was caused by incorrect indexing of the lever and shaft at assembly? Looks like the lever was forced down into (incorrect) position by tightening the retaining screw, smashing the index pin in the process.. In my experience, the lever (if properly indexed) slides onto the shaft and fully seats with little pressure. The screw is only there to retain the lever.

Still no word from the OP on the orientation and location of the pumps, which could also be a factor.

 

[Toobuilder]

The locking pin has nothing to do with this wear. That white round pins purpose is to lock and index the knob to the shaft. That pin is supposed to fill the gap from the flat machined in the shaft. I just don’t see how this got worn the way it appears in the pic unless someone jammed it own on the round part of the shaft instead of the flat. You can’t apply enough rotational force to shear it off, as the shaft has no resistance. The locking is done via a different pin riding in a slot in the body.

After looking at the picture, it appears the pin is smashed, not smeared, so I suspect that someone did just like you suggest; simply placed the lever on the shaft, did not find the indexing feature on the shaft and just cranked the screw down tight, destroying the pin in the process. At that point, the ports are forever misaligned (partially obstructed) compared to the lever. That's strike one. Exacerbating that, is the improper use of the interlock knob which guards the OFF position, but more importantly provides positive positioning for the LEFT/RIGHT operating mode. Without the positive stop, the operator is using visual cues to position the guts of the valve, which also contributes to partial port blockage. That's strike 2.

 

[johnbright]

Hopefully this aircraft is grounded until the keying pin in the knob is repaired or the knob replaced with a new one.

I wonder why the OP uses the term “plastic”, I would think the keying pin that looks white in Post #1 is aluminum. I know the knob is aluminum.

The attached image shows how the safety button locking pin (Andair calls it “safety button which must be raised to switch off the fuel”) engages the valve body.

• The kidney slot allows the handle to rotate 90 deg when the safety button is not raised so the handle can move from left tank to right tank with the safety button not raised.
• The flat-bottom round hole clockwise of the kidney slot locks the handle in the off position. To move the handle to the off position one must raise the safety button. To move handle out of the off position one must likewise raise the safety button.
• The safety button is spring-loaded to the not raised position.

Also in the image one can see the shaft keying feature is a scallop to match the cylindrical pin in the red handle.

 

[lr172]

Larry, my point was I don't believe he is getting the valve turned to the exact position to allow free flow of fuel to the pump. My theory is this is because the white pin is worn and difficult to "feel" the correct position when it is rotated. (Especially when top knob is pulled up) Possibly a clearer meaning of "It’s made changing fuel tanks impossible". I took that as the valve is difficult to rotate and possibly difficult to "feel" the correct position.

I can rotate my valve a few degrees (going from one tank to the other) and I can see a amp reduction (I have a Hall effect sensor on both my Walbro fuel pumps) and hear a slight different pitch the fluid passing through the orifices is making.

I don’t believe a failing fuel valve and 2 Walbro pumps failing very early is a coincidence. Just my opinion of course.

Agree completely. With that pin worn away it will be difficult to get the shaft to turn. Sorry, thought your were talki About the cause

 

[CJT]

Don't think so. You pull the knob to turn the fuel selector "OFF". Switching tanks is just done with a turn of your wrist. That way you can't accidently turn the valve off.

I've got a spare knob if you need to borrow it till your new one arrives. PM me if needed.

Thanks

 

[CJT]

I contacted Andair since they are local to me. They said those pins are a close fit so it's tricky to remove them, the options you have are to machine out the pin and replace but this is difficult as it's a precision part. Alternatively they can ship you a replacement knob which shouldn't be expensive. I have DMed you with a contact email.

Some update
Thanks to your effort, Toren Philip from Andair contacted me
He asked photos of spindle of the fuel valve
After watching them, he identified the problem
The spindle was wrongly filled
The length should hav been at least 13mm long, in my case it’s too short
He advised me to correct it, by buying extension from spruce
Thank you all for your inputs

 

[Toobuilder]

Some update….

Just to understand your post - the Andair valve was manufactured incorrectly, perhaps destroying your fuel pumps in the process, and they want you to purchase an additional part to make it work?

 

[CJT]

Just to understand your post - the Andair valve was manufactured incorrectly, perhaps destroying your fuel pumps in the process, and they want you to purchase an additional part to make it work?

No, the installation was not done correctly