Testing Perkins 4108 lift pump

BlowingOldBoots said:
You keep doing the same thing and getting the same result, I assume you have not raised the test tank to establish a positive head. On your boat is the fuel tank below the level of the engine? If it is not and there is a head of fuel, then that is a different set up from what you have been using. The 'little gravity issue' is likely to be the big issue. Have you tried raising your test tank above the level of the pump? Or even just a longer bit of hose filled with fuel and suspended above pump height.
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I have tried every combination including filling the tube whilst raised.
On the boat my tank highest level is way below the pump.
I have used a rubber bulb pump to actually prime one test set up, the bulb pump forced plenty of fuel through but then operating the mechanical pump passed Zilch.
I can blow through the 'in' valve but not through the out valve.
There has been lots of fuel in the pump(s) to lub up the valves.
I will try again filling the pump chamber as lw395 suggests because, as he says, even on filter change exercises there is probably fuel in the chamber
 
pcatterall said:
I can blow through the 'in' valve but not through the out valve.
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Now try sucking at the pump inlet and the pump outlet

You should be able to suck through the pump outlet and get nothing through the pump inlet

If as I suspect you can suck fuel/air from the inlet that valve is not closing so the pump is just pumping fuel/air in the out again of the pump inlet.

If this is the case the inlet valve seat is damaged or some debris is trapped in the valve or the valve is not seated/sealed in the body of the pump correctly.

This type of diaphragm pump should pump air and/or fuel OK. The pump is very similar to the henderson bulge pump and most water pressure pumps and those will self prime very well by pumping air out of the system.
 
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Rogershaw said:
Now try sucking at the pump inlet and the pump outlet

You should be able to suck through the pump outlet and get nothing through the pump inlet

If as I suspect you can suck fuel/air from the inlet that valve is not closing so the pump is just pumping fuel/air in the out again of the pump inlet.

If this is the case the inlet valve seat is damaged or some debris is trapped in the valve or the valve is not seated/sealed in the body of the pump correctly.
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Or the valve is just not very good with air when it's dry.
In fact to be able to blow air through it, both valves must be open to air.

I suspect there are no springs closing the valves? The valves are closed by the motion of fuel going the wrong way. The motion of air is probably not enough to overcome gravity quickly on the inlet valve. The outlet, you'd expect to shut by gravity.
Once a valve is shut, the diesel will exert enough pressure on it to seal it. Air won't do that, because it compresses as well as leaking out.

It is exactly like the diaphragm bilge pump somebody was discussing on here a few days ago. They tend to be poor at priming sometimes, once half way full of liquid they work fine.
A bilge pump perhaps ought to be designed to reliably prime from dry.
For a fuel lift pump, it is not really an operating requirement.

It's designed to produce a fairly constant pressure at varying volume per rev, pumping a liquid.
If you wanted to design an air pump, you'd do something different.
 
Lw395 is this weeks winner!!
The comment about having some fuel in the pump struck a chord as I realised that even when I have 'primed' my filters after changes or some work there would still be fuel in the system and probably the pumps chamber.
I tested the theory with some clear pipe high up and with an amount of diesel at the top of the pipe ( only a 3" column ) this was enough to , I suppose, give the pump something to 'grip/suck' on anyway it worked! I had previously forced fuel through with the hand 'bulb' but must have allowed that fuel to run out when I switched to the 'proper' fuel pipe. If I had built the priming bulb into the system as I know that many do then I guess that would have worked but I was planning to fit an (auxiliary) electric pump ( which I will now certainly do!).

I tried all 3 pumps and it was the same on them all so I can keep the new one as a spare! After initial priming all 3 worked sucking fuel upward from a tank.
Of passing interest is that all 3 worked as described using the hand lever but none of them using the 'internal' lever, I cant believe they have all miraculously developed the same fault and wonder if there is an explanation for this?
I wanted to get the internal operating rod in the lowest position on the cam to facilitate fitting the pump arm as it is awkward getting the arm over the rod top while fitting the pump over the fixing studs.
I noticed that the rod hardly seemed to move up and down, just about 1/4" max although the lever had around 1/2" movement when out of the engine. I examined the 'spare engine' and noticed that the cam was, indeed, only slightly raised so the 1/4" movement seems to be the maximum the pump needs.
Anyway, a successful outcome thanks to you all. I know have a better in depth understand of the pump and fuel flows through the system which, of course, is one good reason for DIY rather than just giving these jobs to mechanics. ( despite the diesel all over the bench and up my arm from the pipe filling exercise!)
The priming bulb or electric pump that lots of people fit has been shown to be more that just a quicker way of priming but could be the only way if our system has become completely drained.
Thanks again
 
pcatterall said:
Lw395 is this weeks winner!!
....n
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Hopefully, you're the winner if you've got the things working.
Richard and BoB were not wrong, but sometimes reducing things to O level physics gets the point across.
Sometimes not....
The strength of this forum is that there are different people with different angles on things.
Cheers!
 
RichardS said:
The strange thing is that BOB said that in post #2 and I said it in post #3. In fact, I've repeated several times that the pump will not work until it's primed and all the air is out and even told you exactly how to do it :rolleyes:

Richard
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Thanks Richard here is your post 3
"Are you sure that the lever at the engine end is in the right position to enable the manual lever to work and, if you are trying the engine lever, are you operating it quickly enough? I've operated a car mechanical fuel pump by hand and it did work but it needed a lot of vigorous pumping to clear the air through it before it started pumping fuel a lot more efficiently. "

I think that BOB was nearer the mark when he said ensure the fuel line is full and I can only say that on the boat I had pumped fuel believing the pipe to be empty but in reality there was probably fuel further up the pipes or in the pump.

Thanks however for staying with this and your contributions are, as always, welcome

Read more at http://www.ybw.com/forums/showthread.php?506293-Testing-Perkins-4108-lift-pump#0pKrW6QxYvlb7Puq.99
 
pcatterall said:
Thanks Richard here is your post 3
"Are you sure that the lever at the engine end is in the right position to enable the manual lever to work and, if you are trying the engine lever, are you operating it quickly enough? I've operated a car mechanical fuel pump by hand and it did work but it needed a lot of vigorous pumping to clear the air through it before it started pumping fuel a lot more efficiently. "

I think that BOB was nearer the mark when he said ensure the fuel line is full and I can only say that on the boat I had pumped fuel believing the pipe to be empty but in reality there was probably fuel further up the pipes or in the pump.

Thanks however for staying with this and your contributions are, as always, welcome

Read more at http://www.ybw.com/forums/showthread.php?506293-Testing-Perkins-4108-lift-pump#0pKrW6QxYvlb7Puq.99
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Please note my reference in post #3 to "clearing the air before the pump begins to pump fuel more efficiently and, even more specifically, in my post #7 "I wonder whether you have an air lock in the pump as these pumps do not pump air very well unless you pump quickly and there is no air leak on the inlet side. As someone said, raise the fuel level so that it is above the pump and prime the pump by sucking the outlet with the bulb whilst pumping. Once the fuel is pumping lower the fuel container and see if it keeps pumping "uphill".

I don't know how I could have been any clearer ..... and all this was long before good ol' LW395 has appeared on the scene. :encouragement:

Oh well ... you win some, you lose some. ;)

Richard
 
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No Richard, you have helped get a win on this one. I was slightly blinded by previous work on the boat in situ where I thought I had 'primed from dry'.but in fact had not.
LW395 back to basics suggestion was the final piece in the jigsaw that finally penetrated my old brain.
Please continue the good advice, don't be put off by dim wits like me!
 
pcatterall said:
No Richard, you have helped get a win on this one. I was slightly blinded by previous work on the boat in situ where I thought I had 'primed from dry'.but in fact had not.
LW395 back to basics suggestion was the final piece in the jigsaw that finally penetrated my old brain.
Please continue the good advice, don't be put off by dim wits like me!
Click to expand...

Glad to be of help. :)

Richard
 
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