The Stovebolt Site Forums The Shop Area Engine Shop Fuel Level in Glass Bowl Filters & Pumps

I occasionally see a question posted about the glass bowl on a fuel filter or pump not filling completely. The good news is that they should not fill completely.

I shot a video to show the fuel levels in my Durex Moraine GM #986640 fuel filter, and my '52-'55 glass bowl fuel pump that I cobbled together.

< CLICK > Glass bowl video

After I turn off the motor, the glass bowl on the fuel filter usually fills completely. I assume that ...
> Pressure remains in the line between the pump and the carb.
> The pump does not allow the pressure to reverse through the pump.
> So the bowl fills with the pressurized fuel in the line as air and fuel ooze past the float seat in the carb.

Hope that the video answers the question about fuel level.

Awesome! Thanks Lonnie! I'm replacing my old glass fuel pump with a new one that has vac assist this weekend and I was wondering about the fuel level.

I love your glass filter unit!

Great info and photos on filters.
Anybody know where to find a filter element for the Durex Moraine cage bail type? Mine was missing.
Is there any way the paper AC element can be made to fit? Any other ways to improvise?

I don't know of an aftermarket filter element that will fit your Durex Moraine filter body.

I see the filter elements on ebay occationally.

Also, search http://collectorsautosupply.com/
> Select an automobile brands
> Choose "All years" for the year
> Choose "Filters" for the section
You may need to search a number of automobile brands.

I have a .pdf pattern to cut a cork gasket for use between the body and the bowl. If you want it, send me a PM with your email address.

Since this Durex Moraine filter is nicely plumbed in to the original hard lines, could I run it without a filter element until I find an element?
I am planning to put a modern in-line filter between gas tank and fuel pump, at least temporarily (just cleaned the tank).
Thanks for the quick answer, will pm for the gasket pdf.

Yes, you may leave a glass bowl filter-unit inline without a filter.

When searching for the Durex bronze filter element, you will also need the spring if you don't have one. It is bigger at the bottom than at the top. You may find a complete filter unit for about the same price as the element and spring. Nothing on ebay this morning.
< CLICK >

In the 'upright' AC type pumps the glass bowl is the pulsator dome. The air pocket at the top is a vital part of the diaphragm and valve operation.. it provides an amplification effect (increases the vacuum) so improve performance.

I have a free copy of the AC fuel pump rebuild manual at:

http://www.tm9-801.com/tm9-1828a/index.php

Read the first chapter or two.. explains the workings in all its gory details.

pfarber, and others -

Great info, thanks for the link.

Gotta question - Where does the air come from that is in the fuel pump dome? I can understand that air can be trapped in the pump dome when it is installed. But I also see air bubbles entering the dome in my video in the first post in this thread.

Same question for the fuel filter. My filter bowl fills to the top after the engine is stopped and sits for a few minutes. The air pocket returns when I drive it. Where does it come from?

By the way - your videos on decal installation on your website are excellent.
< DECALS AND VIDEOS >

Just and observation, my 50 Buick filter runs at the same level as yours. The air is likely gasses and not pure air.

Lonnie - the "air" you see [absence of liquid, sometimes a vacuum], is the void caused by the pulsating action of the fuel pump and the intermittent opening of the carb needle - the pump has springs and valves that react to movement of the liquid and pressure change caused by fuel use, none of the flow is instantaneous or continuous - the input side of the pump is suction, the output side is pressure, the "lag" introduces the voids and the "air" comes from the tank, entrained with the fuel

Vern - I think the only time that "air" is really vapor is when the supply line is over heated, eg: vapor lock, maintaining a pressure that prevents the fuel pump from pumping

Bill

It's probably not "air"- - -it's vaporized fuel. A little vacuum on a very volatile liquid like gasoline is bound to make a little of it evaporate. That's what happens when a pump "vapor locks"- - - -there's not enough pressure provided by a weak pump to overcome the tendency of the fuel to boil in the pump and the line to the carburetor as the engine gets hot. Once a large volume of vapor accumulates, the pump stops moving liquid- - - -it's just pulsating vapor. The old practice of putting wooden clothespins on the fuel line and/or wrapping the lines with aluminum foil is simply adding an insulator to help keep the lines cool.
Jerry

The glass bowls look like the ones on the Model As. If they are, a Fram 3039 filter will work well. It has a disc on top that gets pinched between the glass and metal housing. No spring is required.

I'm still struggling to understand the flow of fuel through the filtet unit with an empty bowl. Thought I had it figured out a while back when I had it apart to replace the element. But this empty bowl thing has me puzzled.

No, its air. The fuel pump is really a fuel vacuum AND a pump.. it sucks fuel from the tank.. so it would be very difficult for any substantial pressure to develop in the pulsator dome as any excess pressure would vent through the outlet.... also air is compressible (its actually that very principle that makes the pulsator work.

Good grief Charley Brown- - - - -some people actually believe all that claptrap!
Jerry