Ludi Neethling wrote:
Rancherman, thank you so much for your reply and explanation.
This is also how I understand the system. What I cannot comprehend is the fact than almost no air/fuel comes out of the bleeder and the priming knob does not budge (this is with the Facit switched off). After my previous post (later edited) I switched the ignition on to check the flow of fuel out of the bleeder while the Facit is working and it appears to be slow ( I know this is relative). Back in 2016 when I installed the in-line pump I made sure that the psi (I think +-7psi?) was within the parameters posted by other LOST members. I did not physically check the actual flow at the time, so I am concerned that if the Facit is starting to go on the blink the through flow (from tank to diesel pump) could be restricted. Even though the Facit is a free flow unit I am worried about this. I have not removed it yet.
with bleeder open, and facit 'on'... there should be a pretty good stream!
The whole primer pump thing is basically a piston, a spring loaded 'accumulator' of sorts, and a couple of one-way check ball. I haven't had this particular filter head dismantled, perhaps the 'accumulator' is actually integrated within the 'pumper' part itself.
Pump the primer, and pressure builds against the accumulator. (that spring is now compressed) and further attempts to press the pump feels 'stiff'.
When the primer knob is released, and it comes back out, a check ball closes on the OUTLET side of the filter housing, and draws fuel from the tank and into the head. Pressing the knob reverses this; a check ball closes on the INLET, and pressure from your thumb forces fuel out of the piston, and either;
1. tries to push fuel towards the CP3, or
2. compresses a little tiny 'accumulator' within the filter head.
This check ball prevents our built up pressure from simply return back to the tank via the supply line.
So, when the bleeder valve is opened, the built up pressure within the head
(some of it will be the entrapped air itself, as air is compressible , some of it will be the spring inside the accumulator) will squirt out until the pressure is zero.
So on the next 'pumping', and no air is present, it still takes a pump or 2 to achieve 'stiffness'... to preload that accumulator. Open the bleeder, and it squirts solid fuel out until that accumulator spring is relaxed.
Starting and running the engine also relieves that spring tension. This is without any in line or in tank pump.
So, you can pump the pump until you feel resistance.. start the engine... and all that will be 'gone', until you pump it again.
Resistance or stiffness is only felt AT THAT MOMENT. Starting the engine, Sitting overnight (those accumulators are 'ok' for temporary pressure build, but not for extended periods) Their main purpose is to hold pressure long enough to push air out the bleeder when it's open.
Something is going on with your filter head. A stuck check ball, jammed pumper piston, jammed accumulator.. or blocked passageways.. Something is preventing a nice stream of fuel coming out, or pressure to even be built up! The stream should about arc over and hit the middle of the valve cover.
How far are you opening the screw?
I do a 'quick pump' on similar type filter heads. I open the bleeder valve, say a full turn, then simply place my thumb over the end. (bohemian flap valve) pump away!!! light thumb pressure keeps air from going in, but fuel can easily squirt past my thumb. *use a rubber glove if you want.
Allows for fast pumping to fill an empty filter. No screwing around with multiple bleeder open/close/open/close..
Start with the bleeder. open that baby up a whole turn, or even more. you should be able to pump a nice full stream, with 'some resistance'. *basically the resistance of the return spring. Do it several times. Just stick your thumb over the screw for the 'return stroke'.. If still nothing, take the bleeder clear out, and check it for blockage, then see if the pumper is still 'stiff'. It should not have hardly any resistance with an open system.
Now, with an inline or in-tank pump, this accumulator would be probably fully compressed most of the time. The fuel pressure going into the head will keep it pinned down. So any attempts to 'pump up' should be immediately felt with stiffness. (if there is no air!)
5-7 psi is a good all around supply pressure. But there is one element of them; they are a 'stroker' type pump. They aren't 'smooth' by any means. I'm wondering if the pulses have chattered the check balls (extremely light weight springs)! or some other component within your filter head! Lets not go down that quite yet though!
The primer knob should push, smoothly and reasonably easy with the bleeder opened. lets figure this out first!