Anatomy of a Petcock

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Clivester
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Anatomy of a Petcock

Post by Clivester »

After a recent discussion on petcocks on this forum http://www.hondaspree.net/phpBB3/viewto ... =3&t=10107 I realized that I had made some assumptions about the inner workings of the fuel petcock valve. I decided to open one up to confirm how it operates, as this may help those brave few who attempt to get a stuck or debris-filled one working again.

Here is what it looks like cut apart.
Image

The diaphragm is supported by a plastic disc and held in place by a nipple molded into the diaphragm.
Image
Image
The diaphragm itself acts as the valve, making a seal against the case top with a lip.
Image
Here is a diagram for better visualization. If you have a stuck valve you can see where its possible to press the lip region of the diaphragm with a blunt instrument to assist in releasing it (as suggested by noiseguy in the tech docs section).
Image

Interestingly, there appears to be a secondary rubber diaphragm valve just above the vacuum inlet. I surmise that this is present to prevent fuel from draining into the vacuum line in the event that the main diaphragm becomes punctured.
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mousewheels
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Re: Anatomy of a Petcock

Post by mousewheels »

Clivester - nice work, this will be helpful many a time in the future:) :)
carp
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Re: Anatomy of a Petcock

Post by carp »

Good job.Nice pics,that does make it easier to understand.Thanks,Carp
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