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Old 07-26-2012, 02:12 PM
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Feeding a gravity fed fuel pump

This posting is one of shear curiosity ... I was working on a friends car that he just bought and i was looking at the fuel system that the car came with it had a Holley blue pump which as far as I know is a pusher(gravity fed) pump and when I looked at the fuel cell I saw that there were no fittings on the bottom only fittings on the top do i looked inside and saw a large large hose from one of the fittings to the bottomw of the tank. How could the outlets be on the top ... How do you gravity feed a pump when the fuel has to come up a hose to the top of the cell and down to the pump to be pushed to the carb

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Old 07-26-2012, 02:26 PM
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I dont think those pumps have the ability to pull fuel out or up if mounted above the tank.

The pump needs to be mounted below the opening of the inlet tube that is inside that gas tank, it is shipon feed to the inlet of the pump at first.

Once the flow is established the pump will to some degree create some of its own low pressure on the inlet side to aid in the coninual flow of gas out of the tank.

Thats my take on it
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Old 07-26-2012, 03:00 PM
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Most correctly mounted, "pusher" pumps will self prime from a top exit fuel source.

I've seen them mounted high on a front radiator support and draw perfectly from a rear, top exit tank. Not what the pump is designed for..but!!
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Old 07-26-2012, 09:01 PM
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i was stumped cuz it runs great and i couldnt figure how fuel is being delivered when the fuel pump isnt being fed any fuel ... like when you shut the engine down and the fuel runs back down the hose in the tank out of the fuel pump when you go to start it again how does fuel flow up and out against gravity
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Old 07-26-2012, 09:33 PM
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Quote:
Originally Posted by Pupsvette76 View Post
i was stumped cuz it runs great and i couldnt figure how fuel is being delivered when the fuel pump isnt being fed any fuel ... like when you shut the engine down and the fuel runs back down the hose in the tank out of the fuel pump when you go to start it again how does fuel flow up and out against gravity
It's possible there is a check valve in the system that won't allow the line to drain back but that's just a guess. I have a Holley Blue pump on my S10 drag truck that is mounted under the bed at the rear close to the fuel cell but my fuel cell has the line coming out of the back.
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Old 07-26-2012, 10:12 PM
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yeah thats what i expected fittings at the bottom so that the gas theoretically drains out of the tank into the pump to be pumped to the engine
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Old 07-26-2012, 10:46 PM
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Pumped about 25 gallons of old gas out of the 80 gallon belly tank in my dads old boat with a $30 gravity fed pump. It whined for about 30 seconds while it cought prime but it primed up and my dad ran that gas in his POS mower for weeks till it was all gone.
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Old 07-27-2012, 08:38 PM
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Here's my take on it.
The pick up tube in the tank is located near the bottom of the tank so it is under gasoline all the time. The fuel delivery system is sealed. When the pump turns on it is going to start pushing whatever is in the line. That could be air in a new system or one that has been sitting a bit.
A vacuum is created in the line to the tant and gas begins to flow to the pump because of the sucking action.
Once the gas reaches the pump it is pushed ,just like the air that was before it.
It is better to have the pump located below the top of the tank and as close to the tank as possible as they push better then pull.
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Old 07-27-2012, 11:14 PM
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Simple... the inlet has suction and the outlet has pressure. I've used dozens of pumps like this. Most circle track cars are not allowed to have bottom fuel outlets...
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Old 07-28-2012, 10:01 PM
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Really ? I ask because I actually would like to switch me over like that it seems like a cleaner looking setup and would also like to protect my fuel pump better
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