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  #1  
Old 06-09-2014, 10:13 PM
AX-O's Avatar
AX-O AX-O is offline
 
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Default Purge valve return spring

This thread is not intended to be a discussion of if a purge valve is a bad idea or the best thing since sliced bread. It is simply to document one way of adding a spring to keep the purge valve in the position that allows fuel to flow to the spider in the case that the control cable fails. I looked for examples of how people have done this in the past and was not able to find much. Only a few pics of set ups not similar to mine. If you wish to post your set up, please do so. Thanks.

Fuel flows to the spider


Fuel get diverted to right fuel tank


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The information that I post is just that; information and my own personal experiences. You need to weigh out the pros and cons and make up your own mind/decisions. The pictures posted may not show the final stage or configuration. Build at your own risk. Further more, these are my opinions and not those of my employer.
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  #2  
Old 06-10-2014, 12:45 AM
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Nice! That's how I did mine....
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  #3  
Old 06-10-2014, 07:56 AM
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Before this start digressing, please read the first sentence in post 1. Thanks.
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The information that I post is just that; information and my own personal experiences. You need to weigh out the pros and cons and make up your own mind/decisions. The pictures posted may not show the final stage or configuration. Build at your own risk. Further more, these are my opinions and not those of my employer.
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  #4  
Old 06-10-2014, 12:07 PM
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Nice clean approach. The two failures that I know of where not the cable, they where the lock nut, or lack of safety of the nut that holds the arm on.
Good job AC. Check that arm and make sure it is properly safetied.
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  #5  
Old 06-10-2014, 03:30 PM
Tom Martin Tom Martin is offline
 
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The purpose of the spring is to return the arm to full fuel flow if there is a failure in the cable. I see three possible failure modes
1. Cable breaks
2. bolt holding cable comes loose and falls from arm
3. nut holding arm comes off.

The spring, as installed will look after the 1st failure mode. If you were to drill a small hole in the arm and put the spring directly on the arm you would eliminate two of the three failure modes.

Nice work!
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  #6  
Old 06-10-2014, 04:06 PM
N427EF N427EF is offline
 
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Default Belt and suspenders!

It is interesting to note that the manufacturer of the purge valve says no return spring is necessary since it has a built in provision to keep the valve in the open position.
Unlike a throttle arm which on its own generally settle in the closed position and no springs are attached to any throttle cables as far as I know.
Anyway, nice installation and FWIW I too attached a return springs to the purge valve arm.
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  #7  
Old 06-10-2014, 04:16 PM
Bevan Bevan is offline
 
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Quote:
Originally Posted by N427EF View Post
It is interesting to note that the manufacturer of the purge valve says no return spring is necessary since it has a built in provision to keep the valve in the open position.
I am currently working on a spring confuiguration that covers all the bases. I have not seen any statement about the purge valve having a "built in provison" to keep the valve open. Can anyone elaborate/confirm this? If so, how is it done without a spring?

Bevan
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  #8  
Old 06-10-2014, 04:32 PM
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Quote:
Originally Posted by N427EF View Post
It is interesting to note that the manufacturer of the purge valve says no return spring is necessary since it has a built in provision to keep the valve in the open position.
No disrespect intended, but this isnt completely true. The AFP purge valve for example has no built in provision to keep it open. It is true that the manufacturer believes a return spring isnt necessary, but their reasoning is that a high quality control cable should be used that is very unlikely to fail if installed correctly. Installation of a spring to keep the valve open is left to the discretion of the customer.

erich
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  #9  
Old 06-10-2014, 04:37 PM
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Default Purge valve

For my edification, could someone explain what the purge valve does? Please.
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  #10  
Old 06-10-2014, 04:46 PM
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...and the failure point of that cable is where the solid wire exits the little pin vice end attachment assembly. 'been there, done that, wore the pointy cap.
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