Manual fuel tap issues.

[Lucky Phil 1,303]

Well I've finally put this one to bed. Due to available sizes for Viton/FKM seals I eventually had to machine down the oring grooves on the piston to 10.2mm od from the std 10.5 and widen the grooves as well to take a slightly wider 2.4 mm seal from the std 10x2.0mm.

Someone at home with a pedestal drill may be able to do this with a small file and some care. So as shown in the previous image I have slotted the piston and drilled the housing to accept a 4mm grub screw that is now the open stop. I've modified the piston oring grooves as previously outlined and used Viton/FKM seals of 9.8 x 10.4 mm which dont swell in fuel. Put it all together with blue loctite on the grub screw to lock and seal it and you have a tap that doesn't leak and works smoothly and very nicely.

The whole issue is the original Nitrile seals swell in fuel and cause jamming of the piston/plunger. Nitrile seal swelling in fuel isnt an issue between 2 fixed immovable surfaces where it can actually assist sealing but in this situation it's horrible. My main concern is wrenching on the tap when trying to shut it off which is being transmitted through plastic mounted tank integral threaded inserts. Wreck one of these and the tank is scrap. 

So as usual the OEM has literally skimped  pennies on the seals and made the tap in some cases useless.Nice design but looks like the accountants got involved.

   

 

Ciao

[docc 2,686]

Thank you, LuckyPhil, for the excellent insight and sharing!

I wish I had this all done to my Manual Fuel Tap already as I am upon a Tank-off Maintenance  interval and dread twisting on that thing like a knuckle-dragger.

At least I know to isolate the tank with a spanner.  I hope that works until I can preform this excellent modification.

Lucky Phil rocks! 

[Lucky Phil 1,303]

6 minutes ago, docc said:

Thank you, LuckyPhil, for the excellent insight and sharing!

I wish I had this all done to my Manual Fuel Tap already as I am upon a Tank-off Maintenance  interval and dread twisting on that thing like a knuckle-dragger.

At least I know to isolate the tank with a spanner.  I hope that works until I can preform this excellent modification.

Lucky Phil rocks! 

If you need to remove the tap docc I suggest removing the tank fitting and then separating the tap from the fitting in the vise. Maybe Chuck could mod a few for people at a reasonable cost. He's got the equipment to do a superior job to me and he'd do one in under an hour easy.

Ciao

[Weegie 59]

7 hours ago, Lucky Phil said:

Well I've finally put this one to bed. Due to available sizes for Viton/FKM seals I eventually had to machine down the oring grooves on the piston to 10.2mm od from the std 10.5 and widen the grooves as well to take a slightly wider 2.4 mm seal from the std 10x2.0mm.

Someone at home with a pedestal drill may be able to do this with a small file and some care. So as shown in the previous image I have slotted the piston and drilled the housing to accept a 4mm grub screw that is now the open stop. I've modified the piston oring grooves as previously outlined and used Viton/FKM seals of 9.8 x 10.4 mm which dont swell in fuel. Put it all together with blue loctite on the grub screw to lock and seal it and you have a tap that doesn't leak and works smoothly and very nicely.

The whole issue is the original Nitrile seals swell in fuel and cause jamming of the piston/plunger. Nitrile seal swelling in fuel isnt an issue between 2 fixed immovable surfaces where it can actually assist sealing but in this situation it's horrible. My main concern is wrenching on the tap when trying to shut it off which is being transmitted through plastic mounted tank integral threaded inserts. Wreck one of these and the tank is scrap. 

So as usual the OEM has literally skimped  pennies on the seals and made the tap in some cases useless.Nice design but looks like the accountants got involved.

   

 

Ciao

Rolls Royce Piston Aero Engines - a designer remembers by AA Rubbra, liking your taste in reading Phil..........a lot.

A great read, as are many in that series if you love engines

[Lucky Phil 1,303]

1 hour ago, Weegie said:

Rolls Royce Piston Aero Engines - a designer remembers by AA Rubbra, liking your taste in reading Phil..........a lot.

A great read, as are many in that series if you love engines

Yes John, great book. Another good RR one is "Not Much of an engineer" by Stanley Hooker.

Ciao

[docc 2,686]

Pretty sure this topic belongs in "How to . . ."  

I'll be moving it after I make this post. Having taken my tank off this morning for filter changes, I thought how nice it would be to have a functional manual fuel tap /petcock. Pretty inelegant to apply slip-joint pliers, even through, a leather pad, to accomplish fuel shut off.  I did note that my tap needs almost an extra half of a flat to close fully. So, only about 1/12 of a turn. Right annoying.

Thanks, again, Lucky Phil!