CAV filters with pumps on top - where do they vent?

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prv

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Decided (see my other thread) to go with CAV filters for the changeover system on the new boat. Seen ones with built-in priming pumps, which seems handy, but I'm puzzled as to where the air is supposed to vent as you pump the fuel in. The non-pump housings have a vent screw on the top, but the pump version only has a single bolt on top which I assume is the main assembly one. Is there some cunning mechanism in the pump to let air out, or do you need to make your own arrangements? If the latter, is there a ready-made part that will fit in one of the spare outlet ports?

Cheers,

Pete
 
hi
99% of diesel engines have a return line to the fuel tank this will blead of the air to the tank, If you have a lot of air in the system (say you have changed the fillter) then i open the blead screw on the pump to vent of the air as i pump
 
when changing engine filters crack the bleed screw on the housing to force air out with the pumped fuel


prv said:
Decided (see my other thread) to go with CAV filters for the changeover system on the new boat. Seen ones with built-in priming pumps, which seems handy, but I'm puzzled as to where the air is supposed to vent as you pump the fuel in. The non-pump housings have a vent screw on the top, but the pump version only has a single bolt on top which I assume is the main assembly one. Is there some cunning mechanism in the pump to let air out, or do you need to make your own arrangements? If the latter, is there a ready-made part that will fit in one of the spare outlet ports?

Cheers,

Pete
Click to expand...
 
prv said:
Is there some cunning mechanism in the pump to let air out, or do you need to make your own arrangements? If the latter, is there a ready-made part that will fit in one of the spare outlet ports?
Click to expand...

The ones with integral primer pumps come in 2 flavours - 2 port or 4 port. If a 4 port model, you could loosen the outlet blanking plug to vent it. If a 2 port model, you'd have to vent at the secondary filter on the engine.

But, you can get add-on primer pumps for CAV filters; these just bolt on to either an inlet port, so you can still vent using the vent plug on top. See http://www.asap-supplies.com/marine/hand-primers-for-cav-type-fuel-filters
 
oceanpilgrim said:
If you have a lot of air in the system (say you have changed the fillter) then i open the blead screw on the pump to vent of the air as i pump
Click to expand...

sailorman said:
when changing engine filters crack the bleed screw on the housing to force air out with the pumped fuel
Click to expand...

I've just re-read my initial post to see if I'd accidentally said something different to what I meant to. I don't think I did.

"Open the bleed screw" is not a very helpful answer to a question beginning "there is no bleed screw" :rolleyes:

Pete
 
pvb said:
The ones with integral primer pumps come in 2 flavours - 2 port or 4 port. If a 4 port model, you could loosen the outlet blanking plug to vent it. If a 2 port model, you'd have to vent at the secondary filter on the engine.

But, you can get add-on primer pumps for CAV filters; these just bolt on to either an inlet port, so you can still vent using the vent plug on top. See http://www.asap-supplies.com/marine/hand-primers-for-cav-type-fuel-filters
Click to expand...

Thanks. I did consider the add-on pumps, but it seemed a bit daft to get a conversion kit when I was buying new filter heads anyway. It also looked like it would obstruct access to the main bolt and the bleed screw from the front, which is where I need to get at them from.

Plain machine screws don't really work very well as vents (as I discovered when the filter bleed screw on the old boat got blocked, producing the same effect) - so I think what I will do is to drill one of the blanking plugs on each filter to turn it into a bleed screw. Seems crazy that they don't incorporate one in the top as they do for the normal filter heads though!

Pete
 
I have the 4 port with priming button on Little Ship, as already stated the 4 port one has a bleed vent on top. I assume you have the 2 port one fitted. You could always loosen the outlet pipe nut in order to remove the air from the filter.

Tom
 
IMGP0331.jpg
This one has a bleed nipple fitted to the outlet connection.
 
prv said:
Decided (see my other thread) to go with CAV filters for the changeover system on the new boat. Seen ones with built-in priming pumps, which seems handy, but I'm puzzled as to where the air is supposed to vent as you pump the fuel in. The non-pump housings have a vent screw on the top, but the pump version only has a single bolt on top which I assume is the main assembly one. Is there some cunning mechanism in the pump to let air out, or do you need to make your own arrangements? If the latter, is there a ready-made part that will fit in one of the spare outlet ports?

Cheers,

Pete
Click to expand...

Crack any joint which is convenient after the primer pump if you feel the need but in my view its more about seeing whether anything is happening rather than essential because, as has been said, any air will find its way back to the tank via the fuel return pipe. I prefer the inline bulb type of primer because I have had a filter head primer fail and it was a common problem a few years ago although I'm told they have since modified.

Incidentally I have seen banjo bolts with a built in bleed screw.
 
sorry i ment to say bleed screw on inj pump
prv said:
I've just re-read my initial post to see if I'd accidentally said something different to what I meant to. I don't think I did.

"Open the bleed screw" is not a very helpful answer to a question beginning "there is no bleed screw" :rolleyes:

Pete
Click to expand...
 
Daydreamer said:
Crack any joint which is convenient after the primer pump if you feel the need but in my view its more about seeing whether anything is happening rather than essential because, as has been said, any air will find its way back to the tank via the fuel return pipe. I prefer the inline bulb type of primer because I have had a filter head primer fail and it was a common problem a few years ago although I'm told they have since modified.

Incidentally I have seen banjo bolts with a built in bleed screw.
Click to expand...

Here they are http://www.ebay.co.uk/itm/M10-x-1-25-banjo-bolt-with-bleed-screw-nipple-/160724310059 I'm not a fan of undoing unions unless absolutely essential, potential for leaks and all that.
 
LittleShip said:
I have the 4 port with priming button on Little Ship, as already stated the 4 port one has a bleed vent on top. I assume you have the 2 port one fitted.
Click to expand...

Don't have anything fitted yet, but a 4-port with pump is on the way from SSL Diesel Parts.

I can't see where it was "already stated", but if the 4-port pump version has a bleed screw then that's excellent news. It's not visible in any of the photos I've seen though.

Have to wait and see what turns up :). Perhaps they're using old photos.

Pete
 
ghostlymoron said:
This one has a bleed nipple fitted to the outlet connection.
Click to expand...

Thanks, I did see those. There are no banjo fittings in my planned system, though - the inlet and outlet will be copper tube via a compression stud, going to (or coming from) a 3-port valve to provide a changeover facility. I suppose I could add one to one of the blanking ports and then seal off the banjo somehow, but it seems a bit of a bodge.

Pete
 
Daydreamer said:
Crack any joint which is convenient after the primer pump if you feel the need but in my view its more about seeing whether anything is happening rather than essential because, as has been said, any air will find its way back to the tank via the fuel return pipe.
Click to expand...

I'm sure the engine would cope ok with the occasional bubble, and send it back down the return line, but pumping a new filter full of fuel must displace something like three quarters of a litre of air. Can't imagine any engine keeping going through that.

Pete
 
prv said:
Can't imagine any engine keeping going through that.

Pete
Click to expand...

No neither can I. We are, I thought, talking about priming the system to get the fuel to the injector pump(s). A hand operated filter head primer or inline bulb primer wiil easily fill a dry filter and pass the fuel forward because they have a non return valve in them. FWIW on my volvo engine I slacken the banjo on the engine lift pump to check the fuel is there and then use the miserable hand priming lever on that pump and check to see fuel is present on the engine mounted fine filter by slackening the outlet banjo on top of said filter. I do it this way because it takes about as long to do as to write about it and these connections are much more accessible than the filter. It also guarantees that fuel is at the engine rather than just the filter.

It also gives me the best chance of restarting an engine quickly if I were to run out of fuel. Best avoided but as my boat does not (yet) have a fuel gauge this not an impossible situation.
 
prv said:
So, returning to the question with which I opened this thread, where does the air go?

Pete
Click to expand...

Apologies for the lack of clarity. I assumed the answer to your question would be implicit in "on my volvo engine I slacken the banjo on the engine lift pump to check the fuel is there". In operating the primer with that banjo slackened when 'solid' fuel started to appear it would have purged any air out through the joint then I could move on to fill the next filter etc.

Whether or not a primer pump will push all the air past the injector pumps and on to the tank I don't know for certain as I have never bothered to try it.

Anyway I'm just off to fit my nice new filter and primer just received from Simpsons so perhaps I can actually find out :)
 
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