Garry,

Looking at the Perkins 4.108M handbook published in 1979, it appears that
the "fuel oil leakoff pipe" connects the "atomizers" together and then runs
to the tank. This would put it after the fuel injection pump.

Looks like you need some more plumbing....

Good luck,

Ken
S/V Parfait
Raleigh, NC


"Garry Elmer" wrote in message
...
Greetings!
I was wondering if anyone knew the mechanism with which the Perkins 108-4
returns un-used fuel to the tank?

I installed a new electric fuel pump in our system and set the supply
valve
to one tank and the return valve to the other, trying to transfer fuel and
polish it at the same time, with the diesel off. I did not notice any
fuel
being transferred so I assumed that the mechanical lift pump was in the
way.

I replaced the fuel filter on the diesel yesterday and while bleeding the
system at the low pressure inlet to the high pressure pump, had plenty of
fuel flow from the electric pump. Much more than expected from the looks
of
my bilge.

Where does the return fuel line "pick off"? Is there a pressure relief
valve associated with it? Should I be able to transfer fuel by using the
electric fuel pump with the diesel off?

Thanks!

Garry
Mystic, CT
s/v ChrisDaLyn
1983 IRWIN 38 CC
http://www.99main.com/~elmergw/

"Ken Coit" wrote in message .com...
Garry,

Looking at the Perkins 4.108M handbook published in 1979, it appears that
the "fuel oil leakoff pipe" connects the "atomizers" together and then runs
to the tank. This would put it after the fuel injection pump.

Looks like you need some more plumbing....

Good luck,

Ken
S/V Parfait
Raleigh, NC


"Garry Elmer" wrote in message
...
Greetings!
I was wondering if anyone knew the mechanism with which the Perkins 108-4
returns un-used fuel to the tank?

I installed a new electric fuel pump in our system and set the supply
valve
to one tank and the return valve to the other, trying to transfer fuel and
polish it at the same time, with the diesel off. I did not notice any
fuel
being transferred so I assumed that the mechanical lift pump was in the
way.

I replaced the fuel filter on the diesel yesterday and while bleeding the
system at the low pressure inlet to the high pressure pump, had plenty of
fuel flow from the electric pump. Much more than expected from the looks
of
my bilge.

Where does the return fuel line "pick off"? Is there a pressure relief
valve associated with it? Should I be able to transfer fuel by using the
electric fuel pump with the diesel off?


Thanks!

Garry
Mystic, CT
s/v ChrisDaLyn
1983 IRWIN 38 CC
http://www.99main.com/~elmergw/





Gary, the route your fuel takes is from the tank to the
fuel injection pump via the filters and the electric and
mechanical lift pumps; if the engine is not turning, the injection
pump does not work and therefore is not sending guel to the injectors
and not pushing the excess back into the tank.... So you have no hope
of polishing your fuel unless you install an additional fuel line
(with a stop cock) before the injection [ump
john

On Sat, 26 Jul 2003 08:47:53 -0400, "Garry Elmer"
wrote:

Greetings!
I was wondering if anyone knew the mechanism with which the Perkins 108-4
returns un-used fuel to the tank?

I installed a new electric fuel pump in our system and set the supply valve
to one tank and the return valve to the other, trying to transfer fuel and
polish it at the same time, with the diesel off. I did not notice any fuel
being transferred so I assumed that the mechanical lift pump was in the way.

I replaced the fuel filter on the diesel yesterday and while bleeding the
system at the low pressure inlet to the high pressure pump, had plenty of
fuel flow from the electric pump. Much more than expected from the looks of
my bilge.

Where does the return fuel line "pick off"? Is there a pressure relief
valve associated with it? Should I be able to transfer fuel by using the
electric fuel pump with the diesel off?

There's a fuel rail on top of the engine that connects the injectors
together. This rail collects the excess fuel and returns it to the
tank. If there's no flow to the injectors, the fuel won't return. If
you want to polish the fuel, you need another return. You can tee it
into the return to the tank from the engine if you want. But you should
have a check valve on it.

Steve

I have one of these engines as well. Does anyone have an idea of just
how many times per hour of normal engine operation an X gallon fuel tank
would be circulated through the filters? I burn somewhat less than a
gallon of fuel per hour at 2100 rpm and 5.5 knots with a 55 gal. tank.

I had a professional company polish my fuel this spring. The technician
indicated that an hour of polishing would recycle my fuel three times or
at a rate of roughly 150 gallons per hour.

I'm sure that normal running is much less frequent.

Last week my dock-neighbor (Gulf Star 43' trawler w/dual Perkins 6-cyl)
went on the three hour tour returning after 45 minutes because one of
his engines had quit. HIs filters had clogged and starved his starboard
engine. When he replaced the fuel filter it looked like he had used it
as an oil filter before switching it over to fuel duty. I've never seen
a dirtier fuel filter.

Joe Wood

Steven Shelikoff wrote:
On Sat, 26 Jul 2003 08:47:53 -0400, "Garry Elmer"
wrote:


Greetings!
I was wondering if anyone knew the mechanism with which the Perkins 108-4
returns un-used fuel to the tank?

I installed a new electric fuel pump in our system and set the supply valve
to one tank and the return valve to the other, trying to transfer fuel and
polish it at the same time, with the diesel off. I did not notice any fuel
being transferred so I assumed that the mechanical lift pump was in the way.

I replaced the fuel filter on the diesel yesterday and while bleeding the
system at the low pressure inlet to the high pressure pump, had plenty of
fuel flow from the electric pump. Much more than expected from the looks of
my bilge.

Where does the return fuel line "pick off"? Is there a pressure relief
valve associated with it? Should I be able to transfer fuel by using the
electric fuel pump with the diesel off?


There's a fuel rail on top of the engine that connects the injectors
together. This rail collects the excess fuel and returns it to the
tank. If there's no flow to the injectors, the fuel won't return. If
you want to polish the fuel, you need another return. You can tee it
into the return to the tank from the engine if you want. But you should
have a check valve on it.

Steve

.... So you have no hope
of polishing your fuel unless you install an additional fuel line
(with a stop cock) before the injection pump

Yes, but.... A more convenient solution is to add a fuel pressure valve at
that stop cock point and always leave the cock open other then during a
crisis of some sort. I believe you can buy the little spring loaded pressure
valves which will open at 3psi for example.

When the engine is shut down but the electric pump is running, the valve will
automagically open and circulate the fuel back to the tank as desired as long
as the electric pump can make the 3psi or whatever you choose to use. When
the engine is running you'll still be getting at least the 3 psi at the input
to the injector pump, and I'm not sure why one would want more anyhow? Or if
one wants, your stop cock is still there to manually shut off the return
entirely.

Bill