Priming primary fuel filter

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Steve_Sigma33

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I am having a problem getting the primary fuel filter to seal and form a vacuum. It’s the type with the glass water bowl at the bottom with the plastic ‘finger bolt’ that refuses to undo. I know my lifting pump works as I emptied the glass bowl by undoing the bolt at the top that releases the bowl from the filter and successfully reprimed the system yesterday. Today I repeated the process but changed the filter at the top and now no matter what I do I can’t get it to prime.

Does anyone have some hints and tips regards this type of filter?
 
I have a 3 inch length of aluminium pipe with a slot cut in the end with an angle grinder. This fits over the drain plug & I can get into a confined space to release the plug.

I have fitted 2 studs in the bulkhead & the filter is mounted on these. The fuel hose is extra long & I can quickly losed 2 /8mm nuts, lift the filter off the studs & hold it over a bucket. Here I can work on it. Any excess fuel goes in the bucket. Not in the bilge.

I had problems with air leaks for some time. I later found the problem was that the filter unit was a clone & not a genuine CAV one. I bought a new Delphi ( CAV is now Delphi) & since have never had a leak issue. Spanner monkeys complain about them, but providing they are the genuine article they should be problem at all. There are hundreds of thousands of them in use in really difficult conditions all over the world. The filters are cheap, easy to obtain & work.

I never had much luck with the lift pump on my Volvo 2020 MD. I now have a new D1-30F & it has a better lift pump on top of the engine filter. I still do not use it.

I have a belows pump in the fuel line (a diesel one) this drags the fuel through without bothering too much with bleed screws. One can hear the fuel as it goes back into the tank after a few pumps.
typical pump
 
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Is this a CAV type filter? If so, apart from replacing those infernal contraptions with something that is simple to use (yes, I really don't like CAV filters) you will need to dismantle the glass bowl from the filter, remove the filter, make sure the O rings have a good coating of diesel and all the seals are well seated and coated with diesel then reassemble and then cross fingers.

I replaced my CAV filter years ago with a 'top loading' filter that just works

@PaulRainbow often points people to this link Racor Type Diesel Filter FG500
 
On one boat I used to crew on, the problem seemed to be that the lift pump was great at lifting diesel, but not much cop at sucking air.
Fill the CAV via the bleed screw and it all just worked.
1/4 turn valves rither side of the CAV, or at the tank and after the CAV seem like good idea.

Cleaning the tank so you never have to change the CAV at sea seems a top idea!
 
B27 said:
On one boat I used to crew on, the problem seemed to be that the lift pump was great at lifting diesel, but not much cop at sucking air.
Fill the CAV via the bleed screw and it all just worked.
1/4 turn valves rither side of the CAV, or at the tank and after the CAV seem like good idea.

Cleaning the tank so you never have to change the CAV at sea seems a top idea!
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That seems like a really good idea to try. I guess it will also prove if I don’t have a seal quite right also
 
What make of replacement filter? Is it a genuine one? I inherited some clone filters when I bought the current boat and I found the filter was everso smaller. The consequence was the central bolt 'bottomed out' before the filter properly tightened and properly sealed the unit. Looked ok but wasn't, only a matter of millimetres. The rubbish filter would work if there was no glass bowl but wouldn't work with a glass bowl.
 
I have several CAV filters and have no issue with sealing the seal rings. It all about technique.

The trick I use is once the filter and rings are in pace tighten the center screw finger tight then rotate the filter, glass bowl and lower cap to seat the seals correctly.

If the seals are not correctly in place and you just tighten the center screw you will distort the seals and wwill not get a seal properly again

Th issue the OP seems to have is with the drain screw. You need to ensure the seal on the drain screw has not hardened or damage in any way. It should only need to be finger tight.

I also have a printing bulb before the primary filter to allow fuel to be pumped in by pressure rather than by suction. This also will show a leak in the filter if the seals are not fitted correctly
 
rogerthebodger said:
I have several CAV filters and have no issue with sealing the seal rings. It all about technique.
Click to expand...
It's also about being aware that the two O rings are NOT the same size, but they're close enough that it's easy to get them wrong, especially when you're upside down, head in the engine compartment, the boat's leaping around and you crew is screaming that the rocks are getting closer.

On Jissel, after a blocked filter resulted in a rather fraught entry into Portsmouth Harbour under sail, I sacked my single CAV and replaced it with a pair of spin-on filters from a car breaker, plus some taps from ASAP, so I ran on one filter, but had a second primed and ready to go. Switching was a matter of seconds, but, of course, I never had to. I also stopped regarding fuel filters as service items, and just changed them when they got rusty enough to be a concern which, over the years, more than paid for the conversion.

My top tip for priming a non-gravity-fed filter is to put one of these in the line close to the tank.

images

That way, you're pushing non-compressible fuel rather than trying to create a vacuum to suck it through.
 
One of the common issues with cav filters is fitting new seals but not noticing the top one is still in place as it sits in a groove, once you get two seals in you are highly likely to get an air leak.
The racor copies are now very cheap and much easier to use.
If you have a pela type suction pump for oil changes use that on the bleed screw instead of the priming lever, takes seconds to suck the system free of air.
 
I have also dumped my CAV filter and fitted a screw on type filter - so much easier and very simple and quick to change. The original CAV filters in my opinion were a PITA, especially as they always seem to have been fitted in inaccessible places, sealing rings to replace every time, difficult to get them to seal properly, getting soaked in diesel etc. The screw on filters just need a smear of oil on the fitted rubber gasket and just screw it up, so easy and quick. The only difference is that there is not a glass bowl which I have never missed. As mentioned the Racor copy filters are also good.
 
Because my fuel tanks are low down in the keels it was a matter of necessity to fit an inline facnor fuel pump which is a great help as it pushes fuel through the system rather than trying to suck it up.
 
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