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  #1  
Old 08-07-2017, 06:41 PM
rlmccarter rlmccarter is offline
 
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Location: Charlotte, NC
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Default 90 Degree Bends and Fuel Cavitation

Hi Guys,

Have any of you experienced cavitation (aka vaporization) due to 90 degree fittings on the supply side of your pump?

I'm putting an SDS injection system on the -8 and just bolted in the beautiful twin pumps. They are a tight fit so I have 90 degree fittings on intake and output. To make it interesting, I'm also using an Andair valve with 90 degree fittings. The tanks of course have 90 degree fittings coming out of them.

So tracing the fuel from the tank it will go through five 90 degree bends: at the tank exit, the valve entrance, in the valve, the valve exit, and the fitting into the pump.

I can eliminate three of the five bends by drilling four more holes in the floorboard to reorient the pump and getting straight connectors into the Andair. I might want to use mogas in the future, but this is just a four cylinder engine. The fuel flow can't be that high. Am I obsessing?



Cheers,
Bob
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  #2  
Old 08-07-2017, 07:14 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by rlmccarter View Post
Am I obsessing?..
Nope.

Anything you can do to reduce the number of 90's on the supply side is a good thing.

Remember that even at idle, the pump is going to be pushing a lot of fuel through the bypass regulator so the fuel flow (vs. consumption) is going to be high. Get the pump as low as possible relative to the fuel tanks and as close as you can to them. Im not a fan of the stock -8 pump location, but its a lot of work to move it.

My SDS pump module is in the stick well on my Rocket with "zero" 90's on the suction side. A major plumbing headache, but worth it to me.

The -8 and Rocket are quite different, but my pictures are found here:

http://www.homebuiltairplanes.com/fo...l=1#post392515

Might give you some ideas
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Last edited by Toobuilder : 08-07-2017 at 07:30 PM.
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  #3  
Old 08-07-2017, 07:17 PM
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Also... After looking at the picture it appears you have the module backwards. (The inlet filter is on the firewall side). Am I seeing something funny?
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Michael Robinson
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PA-20-inspired "family truckster" -in work
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  #4  
Old 08-08-2017, 06:21 AM
rlmccarter rlmccarter is offline
 
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Default Rerouting begins!

Hey Michael,

Good points.

Yup I had the inlet toward the front as an intentional part of the fuel tubing plan.

Based on this I'm changing plans to mount the pump about an inch above the floor on brackets and orienting the inlet aft. That will give straight routing into the pump. I will also put straight AN-6 connectors on the Andair supply side inlets.

Thanks for the sanity check and quick reply!

Bob
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Old 08-08-2017, 06:47 AM
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Also, dont worry about a 90 at the outlet if it helps make the strain relief loop to the firewall - at 50 PSI it wont even notice.
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Michael Robinson
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying
PA-20-inspired "family truckster" -in work
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  #6  
Old 08-08-2017, 08:44 AM
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Carl Froehlich Carl Froehlich is offline
 
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Consider mounting the pump vertically on the gear tower forward side. This allows for smooth loops to/from the pump, and provides some flex tolerance. I try to avoid short straight rigid tubing hard mounted at both ends.

Carl
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Old 08-08-2017, 10:05 AM
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Vertical mounting raises the pump inlets even higher than they are now. You want them as low as possible relative to the fuel.
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Michael Robinson
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Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
PA-20-inspired "family truckster" -in work
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  #8  
Old 08-08-2017, 11:44 AM
TS Flightlines TS Flightlines is offline
 
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the pump plumbing is easy compared to the the Andair Duplex in a tight area!

Tom
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  #9  
Old 08-08-2017, 06:34 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Vertical mounting raises the pump inlets even higher than they are now. You want them as low as possible relative to the fuel.
Pump lift is an issue - however on a vertical pump with inlet at the bottom and outlet looped back down to inlet height it would have just the fluid flow drag of the pipe itself - about the same if the pump was horizontally mounted.

Carl
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Old 08-08-2017, 07:02 PM
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A valid perspective if you consider the inlet of the pump "module" synonymous with the impeller location. I could be wrong, but I think of the impeller plane as the salient "inlet" WRT fuel level. And in a vertical mounting, the impeller plane of the pump is going to be notably higher than if horizontal.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
PA-20-inspired "family truckster" -in work
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