electric priming pump, well, not priming

[tipsyravensaili]

Hiya all!

I am in possession of a formosa 41 w/ a perkins 4108

The fuel system follows this arrangment:

tank -> electric prime pump -> racor -> lift pump on block -> filter on block

or

tank -> racor -> ...


The electric priming pump isn't doing what i thought it was supposed to do.

There's a valve on the inlet side of the racor that seems to turn off the flow to the filter, or a selection?

I took the line off the lift pump and found that i could blow air back through the system and into the tank, implying i have the valve (its unlabeled) in the right position on the racor inlet.

with everything connected back up, the electric pump doesn't pump. Its pretty obvious as there's no fuel in the line before the pump. There was fuel in both filters, before i fussed with it, and there's about 40 gals of diesel in the tank.

I'm pretty much at a loss as to what i should do next to solve the problem... i'll be topping off the filters to try that but it'll leave a giant air bubble in the line i think prior to hte filters. There's no check valve anywhere either between pump and tank so i'm also a little confused as to how the fuel wouldn't just flow backwards into the tank anyway.

So. yeah. now that i've rambled a bit, help?

[tipsyravensaili]

i drew up a sketch, in hope that it might help

https://scontent-lax3-1.xx.fbcdn.net...2d&oe=5DE61736

i hope this link works, i had to put the graphic on facebook as i can't seem to add it direct to the forum

[GordMay]

Greetings and welcome aboard the CF, tipsy'.


FWIW - you probably know:
The filtre should be in line before the electric lift pump (your second scenario), to protect the pump from particulates, and because pumps emulsify water, hindering filtre performance.
Valves are generally open when operator handle is in line (parallel to) with flow, and closed when at 90 degrees (perpendicular to) to flow.

[OldGreyB]

Was the system working and engine running before you worked on it?

I'll assume it was working for PO. So if the pump runs and the bottom valve is in the correct position (since you can blow back through it), take off the hose from the downstream of the manual pump.

Run the electric pump and it should bleed through the Racor, as you may have an air block downstream of the electric pump. Once the Racor is filled, you will then have diesel coming out (into a container) before the manual pump. Reconnect and back off the hose before the injectors or at the injectors so you can bleed out all the air right to the injectors before you go for a restarts.

The pumps normally have internal non return valves, so stop backflow. There should be a diesel return line to the tank- that returns unutilized fuel to the tank, just not shown on your otherwise good diagram

Caution, if you are cranking the motor during the final bleeding, ensure the water cooling sea cock is closed so you do not hydraulic the motor prior to getting it to start. Ensure you open it when the engine runs. See many separate warnings on this on other CF threads under the Engines and Propulsion Systems (Hydrolocking)

[Lepke]

Electric fuel pumps and lift pumps have a builtin valve on each side that function like check valves. They only allow fuel to move toward the engine, not back toward the tank. You could have tank debris stuck in one of the electric pumps valves or a failed valve.

The electric pump should be after the Racor and doesn't need separate plumbing. The electric pump can be directly in line with the lift pump. Either pump will draw thru the other. In the event of a lift pump failure, the electric pump will fuel the 4108.
MY 4108 is running a generator. I have a electric between the lift pump and the Racor. It makes filter changes and bleeding easy. My 2 mains and 2 generators, all have an added electric pump for filter changes and as an emergency standby.

[zeehag]

electric pumps fail. mine is in line after racor and before lift pump. check all hose clamps and hoses and pickup and connectors and pump itself.....buy not the 50 buck pump from autozone but the 75 usd pump from napa... longevity is essential. reliability is important ,and buy 2.. needs a spare.

[Poche]

How do you bleed the air from the Racor if the electric fuel pump is after it? Gravity from the fuel tank? Isn't the purpose of the prime pump to pressure the line to the Racor?
My system has a separate loop for the prime pump with a two way valve before it. So, you turn the valve for the fuel to run through the prime pump and that goes to the primary filter and the rest of the fuel line while you bleed the air. After the system is bled you turn the two way valve back to run fuel straight from the tank to the primary filter. It seems more logical to me.

[Q Xopa]

Originally Posted by Poche

How do you bleed the air from the Racor if the electric fuel pump is after it? Gravity from the fuel tank? Isn't the purpose of the prime pump to pressure the line to the Racor?
My system has a separate loop for the prime pump with a two way valve before it. So, you turn the valve for the fuel to run through the prime pump and that goes to the primary filter and the rest of the fuel line while you bleed the air. After the system is bled you turn the two way valve back to run fuel straight from the tank to the primary filter. It seems more logical to me.

I agree with what you are saying. This is the way I have done it too.
Of course there are many ways people do skin this cat.

[Poche]

Originally Posted by Q Xopa

I agree with what you are saying. This is the way I have done it too.
Of course there are many ways people do skin this cat.Attachment 198969

If one can change the primary filter element without introducing air it does not appear to matter which side the prime pump is. But I think it is not likely to avoid any air.
It appears that most install their prime pump after the primary filter.