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  View original topic: Electric fuel pump + fuel filter
herbie1200 Thu Apr 28, 2016 11:49 pm

I want an in-line electric fuel pump, just to help mechanical fuel pump when, after 20-30days of engine sitting, I have to crank for 20-30secs before starting.

My criteria were:

- fuel pump shall be firmly fixed to the chassis
- low pressure connections can be left without clamp
- fuel filter shall be fixed only with a plastic ring, to be easily removed; the ring is around front right brake line bracket
- fuel filter shall be swappable by simply removing a wheel
- both fuel filter and pump shoud lay in horizontal position

Well, I decided for this arrangement:



Comments and hints about my installation?

P.S. clamp on pump outlet was still not installed

Abscate Fri Apr 29, 2016 3:26 am

Wiring needs chafe protection and also should be tied down to prevent motion.

Plastic case of fuel filter also needs chafe protection, maybe a rubber base?

Looks good

Slow 1200 Fri Apr 29, 2016 3:27 am

did you use a relay for the pump?

herbie1200 Fri Apr 29, 2016 5:38 am

Thank you

This fuel pump is only for emergency, when fuel line or carburetor bowl gets empty.

So I did not install a relay, the pump is simply activated by a push button under dashboard only when necessary.

HRVW Sat Apr 30, 2016 12:39 pm

:-k :-k Drawback I have with a plastic filter under the gas tank or above the tranny is when they leak and you have a near full tank and are at a store shopping. Gas is leaking/pouring on the ground, how does a person crawl under to repair w/o getting a GAS BATH.

I have repaired many leaks under a car (business) and always got a bath wetting my shirt and arm pits...thanx but NO thanx.

mukluk Sun May 01, 2016 10:23 am

HRVW wrote: how does a person crawl under to repair w/o getting a GAS BATH.

Keep one of these in your tool kit in the car: http://www.toolaid.com/content/hose-clamp-pliers-set-0

I've been using these for years, work like a champ to clamp off fluid flow while you disconnect the lines/hoses for repairs.

herbie1200 Thu Jun 23, 2016 7:12 am

Tried the whole system...it does not work!

If I run the el.pump for 2-3 seconds a small fuel pressure grows into the pipe segment from electric pump ---> mechanical pump.

The electric pump, also when off, act as a non-return valve, and the pressure is mantained.

With this pressure "before" the mechanical pump DOES NOT WORK! So if I start the engine it runs until carburetor bowl becomes empty then stops running.

The same if, when cruising, I push for a few seconds the el.pump switch: the pressure locks the mech. pump and after 200-300meters (bowl empting) engine dies.

The only way to reactivate mechanical fuel pump is to temporarily disconnect the 'in' hose, let some fuel to escape ("Puff!") and reconnect it, whith pressure dropped.

Analog issue when I park with very hot engine: hot fuel increases pressure and the no-return function of the el.pump does not allow fuel pressure to return into gas tank, so mech.pump is locked and engine does not start.

It is for me a very strange behaviour; a small "input" pressure seems to lock the mechanical fuel pump. Why???

flyboy161 Thu Jun 23, 2016 9:20 am

Apple and oranges my friend. There is a reason that electric pumps are used in lieu of mechanical pumps and not with them and you just found it.

The VW fuel system works on a suction basis. The tank is vented so that the head pressure (atmospheric) pushes on top of the fuel in the tank. The low pressure in the fuel line draws the fuel to the pump and then it pumps the fuel to the carburetor. Try to seal a straw to a drink using a rubber plug Ina bottle. Eventually you'll collapse the straw and die of thirst because no drink is coming out. So, venting is crucial. If you put a pressure gauge on the fuel line from the tank to pump you'll not read positive pressure ever. It'll be negative pressure. Suction.

Next at the pump itself is a check valve in the top. The pump is comprised of a lever at the bottom which is moved up and down by the push rod coming out of the phenolic block. That in turn moves the pump diaphragm up. A large spring on top of the pump diaphragm pushes it down. As the push Rod withdraws into the block the diaphragm moves down creating suction. Above the pump diaphragm spring is cut off valve diaphragm and above that a smaller spring. As the rod begins to travel up it creates a positive pressure and the larger pump diaphragm spring overcomes the pressure of the cut off valve spring and the cut off valve closes shuttling off fuel from the tank and pushing the fuel in the pump to the carburetor. So that's normal operation. Why doesn't your idea work?

Because pressurizing the fuel line from the tank causes pressure within the pump to overcome the spring pressure of the cutoff valve diaphragm and the cutoff valve closes. Your mechanical pump has in essence become a shutoff valve (and a very effective one at that). It's as though your mechanical pump is in pump mode all the time, not allowing any fuel into the pump body from the tank.

This is operator induced vapor lock. It was a great idea, for sure, but the only way to overcome the problem is a) Ditch the mechanical pump and only run the electric pump, or b) only run the mechanical pump.

flyboy161 Thu Jun 23, 2016 9:41 am

Look at the bright side, you've invented the perfect anti-theft device. Put a pressure relief circuit in it and when you stop some where, bump the switch for the pump and vapor lock the pump. Come out to go, actuate the pressure relief and drive away.

herbie1200 Thu Jun 23, 2016 11:16 pm

Thanks for your appropriate considerations.

The electric pump I have is also a diaphragm pump, so I have the "inducted vapour-lock" effect.

The way to solve this problem: I bypassed the mechanical fuel with a one-way valve, from IN to OUT.

So any pressure from the IN line is blown to the OUT section and goes into the carburetor. Vapour is burped, liquid flows to the bowl vane; if vane is full, only to wait that engine uses some fuel to enable fuel entering.

Now all seems to work; in case of vapour lock or empty inlet line just a few seconds of el.pump to refill carburetor bowl, then the engine starts almost immediately.

But now I suspect a new issue: the bypass valve is metallic and subject to temperature inside engine vane. Will this make the fuel too hot, increasing fuel vaporisation?

flyboy161 Fri Jun 24, 2016 12:02 am

No, I don't think heat induction will be a factor. Sounds like a good fix. Did you run two separate lines back or just use the factory line? I'd be interested in a schematic of the setup.

herbie1200 Mon Jun 27, 2016 12:23 am

OK This is the whole arrangement:



If pressure into the original fuel line increases, due to vapour or accidental elec.pump action, this pressure goes into carburetor via the no-return valve.

Also fuel pressure given by mechanical pump goes to carburetor without returning to the tank, effect of the non return valve.

As I stated for now I'm thinking about fuel boiling into the no return valve, that is heat exposed into the engine vane.[/img]

flyboy161 Mon Jun 27, 2016 12:34 am

Brilliant! Absolutely brilliant! I don't think you'll have issues with boiling fuel. I'm not sure what vane you are referring to. Would you be so kind to post a picture of the no return valve and its location? This way I might understand.

The only concern I would have is the pressure from the electric pump inside the mechanical pump whilst the engine is running. The potential for damage to the pump diaphragm or the stop valve diaphragm is greater when in a liquid locked state. However, the check valve you have installed should relieve that back pressure. So, perhaps I am just overly cautious. It is still a brilliant idea.

herbie1200 Mon Jun 27, 2016 11:54 pm

flyboy161 wrote:
The only concern I would have is the pressure from the electric pump inside the mechanical pump whilst the engine is running. The potential for damage to the pump diaphragm or the stop valve diaphragm is greater when in a liquid locked state. However, the check valve you have installed should relieve that back pressure. So, perhaps I am just overly cautious. It is still a brilliant idea.

The concept is to use electrical pump only for 2-3 seconds and only when, after a sitting of 2-3 week, a long cranking action should be requested to refill carburetor bowl.

After 2-3 week, if battery is not 100%, the risk is to empty battery only to pump fuel and, when fuel is avaible, battery is no more able to spin the engine enough.

The other use of my arrangement is when I get, rarely, vapour lock. An exampe: Highway, engine very hot, I stop for a coffee, after 10 minutes engine is vapour-locked. With my arrangement, a short electric fuel pump action let the vapour to "burp" and engine restarts easily.

flyboy161 Tue Jun 28, 2016 5:38 am

I think you're battery will be fine, even after 2-3 weeks. Definitely the filling of the fuel bowl will help.

=D>



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