Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.

On 4 Feb 2007 18:43:01 -0800, "Frogwatch"
wrote:

Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.


I'm visualizing an old style mechanical pump once used for getting
gasoline to the engine.
A cam pushes a diaphram against a spring. Fuel feeds out while the
spring extends. No flow, no spring movement - no push from the cam
driven finger.

And I'm visualizing an old style electric pulse pump, where a solenoid
prodes the same push as the mechanical finger of the old mech pump.
The contacts don't force another pulse, til the spring returns when
fuel has flowed away..

But now, fuel pumps are often centrifugal and don't stop n wait.

Brian Whatcott Altus OK

On Feb 4, 10:00 pm, Brian Whatcott wrote:
On 4 Feb 2007 18:43:01 -0800, "Frogwatch"
wrote:

Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.

I'm visualizing an old style mechanical pump once used for getting
gasoline to the engine.
A cam pushes a diaphram against a spring. Fuel feeds out while the
spring extends. No flow, no spring movement - no push from the cam
driven finger.

And I'm visualizing an old style electric pulse pump, where a solenoid
prodes the same push as the mechanical finger of the old mech pump.
The contacts don't force another pulse, til the spring returns when
fuel has flowed away..

But now, fuel pumps are often centrifugal and don't stop n wait.

Brian Whatcott Altus OK

Brian:

You could be right, the old pump was a diaphragm type and I think the
new one is rotary cuz it sure sounds like it.

If you're going to use an electric, I would recommend a "rattle" pump
available at any autoparts store. They cost $30, are self priming, cut off
when not needed, and last a long time. I've used them on many gas, and one
diesel, engines. They've never let me down.

My 2 cents,
Bill Longyard



"Frogwatch" wrote in message
ups.com...
Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.

"William Longyard" wrote in message
hlink.net...
If you're going to use an electric, I would recommend a "rattle" pump
available at any autoparts store. They cost $30, are self priming, cut
off when not needed, and last a long time. I've used them on many gas, and
one diesel, engines. They've never let me down.

My 2 cents,
Bill Longyard



"Frogwatch" wrote in message
ups.com...
Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.


cut off
when not needed

How do they know when they are not needed?

Sounds like the first pump had some kind of pressure switch included while
the second does not. I thought most diesel engines had a fuel recirculation
line that led excess fule from the injectors back to the tank. As such when
you run an electric pump it just pumps fuel through the lines, across the
top of the injectors and back to the tank. Not a problem if it continues to
run while switched on.

The "rattle" pump is pressure sensitive and cuts off when not needed. As
far as recirculation goes when used with a diesel, rattle pumps are used a
supplements for either weak injector pumps (which keeps is original
recirculation plumbing), or as replacement "lift pumps" which send fuel to a
good IP which, again, retains in recirc. feature.

Bill Longyard


"Gordon Wedman" wrote in message
news:HAPxh.34319$Fd.30102@edtnps90...

"William Longyard" wrote in message
hlink.net...
If you're going to use an electric, I would recommend a "rattle" pump
available at any autoparts store. They cost $30, are self priming, cut
off when not needed, and last a long time. I've used them on many gas,
and one diesel, engines. They've never let me down.

My 2 cents,
Bill Longyard



"Frogwatch" wrote in message
ups.com...
Years ago, I put an electric fuel pump in line with my mechanical pump
to help in bleeding the fuel system. When I turned the key, it would
run till the system was pressurized and would then stop. If it ran a
lot, I knew I had to bleed the system. It finally had the diaphragm
go bad so I replaced it but was unable to get an exact replacement.
The new pump runs ALL the time unless I turn the key off and if I
allow it to run all the time it gets hot. Did I get two different
kinds of pump? Was the first a "demand pump" that turns off when the
output side is pressurized? Neither set of directions said anything
about this.


cut off
when not needed

How do they know when they are not needed?

Sounds like the first pump had some kind of pressure switch included while
the second does not. I thought most diesel engines had a fuel
recirculation line that led excess fule from the injectors back to the
tank. As such when you run an electric pump it just pumps fuel through
the lines, across the top of the injectors and back to the tank. Not a
problem if it continues to run while switched on.