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This is a very old thread, but can anyone think of a reason why a CAV filter/water separator couldn't be plumbed in in reverse, so that incoming fuel first enters the water bowl, passes up through the filter element and out through its top on its way to the engine?

 

The arrows on the filter head indicate the reverse, but maybe drops of water and bits of muck would be better held in the water bowl before the fuel passes through the paper element; any thoughts?

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23 minutes ago, Bargebuilder said:

This is a very old thread, but can anyone think of a reason why a CAV filter/water separator couldn't be plumbed in in reverse, so that incoming fuel first enters the water bowl, passes up through the filter element and out through its top on its way to the engine?

 

The arrows on the filter head indicate the reverse, but maybe drops of water and bits of muck would be better held in the water bowl before the fuel passes through the paper element; any thoughts?

I have a feeling but not checked this is covered in Tony's excellent web site. Far better than I can tell it

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1 hour ago, Bargebuilder said:

This is a very old thread, but can anyone think of a reason why a CAV filter/water separator couldn't be plumbed in in reverse, so that incoming fuel first enters the water bowl, passes up through the filter element and out through its top on its way to the engine?

 

The arrows on the filter head indicate the reverse, but maybe drops of water and bits of muck would be better held in the water bowl before the fuel passes through the paper element; any thoughts?

 

That is the way the fuel should flow - into the bowl, through the filter, out the top. There is nothing to stop you plumbing it the other way but why would you want to store the water and muck in the small volume inside the filter element rather than in the bowl that can have an extra extension fitted to store more horrible stuff.

 

I think that what might be causing confusion is the two types of filer that can be fitted to these units. The ordinary pleated filters have a solid top plate sealed to the nose on the filter head by an O ring, so fuel has to flow over the plate to the sides and then down into the bowl and through the pleated filter paper. It also has a solid bottom plate.

 

The pleated filters have a punched top plate, still sealed to the nose so fuel can flow down through the filter and through the sides of the "pocket". It then continues to flow downwards through holes in the baseplate that are baffled to impart some spin on the flow. The centre of the filter is an "oversized" metal tube sealed to the bottom and top plate that provides the outlet path.

Edited by Tony Brooks
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24 minutes ago, Tony Brooks said:

 

That is the way the fuel should flow - into the bowl, through the filter, out the top. There is nothing to stop you plumbing it the other way but why would you want to store the water and muck in the small volume inside the filter element rather than in the bowl that can have an extra extension fitted to store more horrible stuff.

 

I think that what might be causing confusion is the two types of filer that can be fitted to these units. The ordinary pleated filters have a solid top plate sealed to the nose on the filter head by an O ring, so fuel has to flow over the plate to the sides and then down into the bowl and through the pleated filter paper. It also has a solid bottom plate.

 

The pleated filters have a punched top plate, still sealed to the nose so fuel can flow down through the filter and through the sides of the "pocket". It then continues to flow downwards through holes in the baseplate that are baffled to impart some spin on the flow. The centre of the filter is an "oversized" metal tube sealed to the bottom and top plate that provides the outlet path.

Hi Tony, thanks for the reply.

 

I agree with you, that the fuel should flow as you describe.

 

The CAV filter body I am looking at has two inlets and two outlets identified by arrows and the inlets open directly above the filter element. 

I have a filter element that is punched with holes at the top and has baffled, directional slots at the base.

The filtered fuel having passed through the element top to bottom into the water bowl at the bottom, passes up the tube in the centre of the element and on towards the engine.

That is the way the arrows intend it to work.

 

I would prefer to plumb it the way you recommend in your first paragraph for the reasons you mention, but this seems not to be what the manufacturer suggests.

 

Can you think of a reason why the fuel flow cannot be reversed so that it is introduced down the centre tube and into the water bowl first?

 

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19 minutes ago, Bargebuilder said:

Hi Tony, thanks for the reply.

 

I agree with you, that the fuel should flow as you describe.

 

The CAV filter body I am looking at has two inlets and two outlets identified by arrows and the inlets open directly above the filter element. 

I have a filter element that is punched with holes at the top and has baffled, directional slots at the base.

The filtered fuel having passed through the element top to bottom into the water bowl at the bottom, passes up the tube in the centre of the element and on towards the engine.

That is the way the arrows intend it to work.

 

I would prefer to plumb it the way you recommend in your first paragraph for the reasons you mention, but this seems not to be what the manufacturer suggests.

 

Can you think of a reason why the fuel flow cannot be reversed so that it is introduced down the centre tube and into the water bowl first?

 

No, I can't. Never given it a thought but seems it would work either way. The only thing I can think is that if the fuel foams up it may be better the way it is designed but its arbitrary.

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2 hours ago, Bargebuilder said:

Hi Tony, thanks for the reply.

 

I agree with you, that the fuel should flow as you describe.

 

The CAV filter body I am looking at has two inlets and two outlets identified by arrows and the inlets open directly above the filter element. 

I have a filter element that is punched with holes at the top and has baffled, directional slots at the base.

The filtered fuel having passed through the element top to bottom into the water bowl at the bottom, passes up the tube in the centre of the element and on towards the engine.

That is the way the arrows intend it to work.

 

I would prefer to plumb it the way you recommend in your first paragraph for the reasons you mention, but this seems not to be what the manufacturer suggests.

 

Can you think of a reason why the fuel flow cannot be reversed so that it is introduced down the centre tube and into the water bowl first?

 

 

The way agglomeators work is that ting droplets of water that can not pass through the filter paper start to build up on the surface because they can't get through the small pores. As they build up they merge like rain in a window and get larger. Eventually the fuel pressure over the area of the drop's surface creates sufficient pressure in the drop to force it through the small pore, so now you have a large water drop on the clean side. The drop is much larger and thus heavier than the original droplets so it can far more readily drop through the clean fuel. The baffles on the holes in the bottom of the filter will cause the fuel to rotate in the bowl and centrifuge (to a degree) the large droplets to the side while the lighter fuel turns 180 degrees to exit up the centre hole sans the water that collects in the bowl.

 

If you reverse the flow the larger water drops will just lay in the bottom of the pockets and gradually build up. There is far less space in the pockets than in the bowl. Also, if the fuel flow manages to lift the water drops there will be no centrifugal effect to spin the water to the side (no angled baffles on the top) but is will also be very close to what will now be the clean fuel outlet, and as the top of these filters has a rim water is likely to build up on it, bringing it even closer to the "outlet" port (note: the question relates to reversing the flow through the filter so this "outlet" is really the inlet as designed).

 

Will it clean dirt and dust from the fuel - yes.

Will it clear water droplets - up to a point probably yes but at a much reduces service life.

Will a glass/plastic bowl or the drain tap ever show ann water - almost certainly no.

 

Is that the filter manufacturer or the engine manufacturer? If you look at the photos that RLWP posted on the previous page you can work out from the arrows which way CAV designed it.

 

 

 

3 hours ago, Bargebuilder said:

This is a very old thread, but can anyone think of a reason why a CAV filter/water separator couldn't be plumbed in in reverse, so that incoming fuel first enters the water bowl, passes up through the filter element and out through its top on its way to the engine?

 

The arrows on the filter head indicate the reverse, but maybe drops of water and bits of muck would be better held in the water bowl before the fuel passes through the paper element; any thoughts?

 

I think that you have this wrong. Pleated filters will store both muck and water in the bowl. pocket filter will store water in the bowl and muck in the filter pockets.

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1 hour ago, Tony Brooks said:

 

The way agglomeators work is that ting droplets of water that can not pass through the filter paper start to build up on the surface because they can't get through the small pores. As they build up they merge like rain in a window and get larger. Eventually the fuel pressure over the area of the drop's surface creates sufficient pressure in the drop to force it through the small pore, so now you have a large water drop on the clean side. The drop is much larger and thus heavier than the original droplets so it can far more readily drop through the clean fuel. The baffles on the holes in the bottom of the filter will cause the fuel to rotate in the bowl and centrifuge (to a degree) the large droplets to the side while the lighter fuel turns 180 degrees to exit up the centre hole sans the water that collects in the bowl.

 

If you reverse the flow the larger water drops will just lay in the bottom of the pockets and gradually build up. There is far less space in the pockets than in the bowl. Also, if the fuel flow manages to lift the water drops there will be no centrifugal effect to spin the water to the side (no angled baffles on the top) but is will also be very close to what will now be the clean fuel outlet, and as the top of these filters has a rim water is likely to build up on it, bringing it even closer to the "outlet" port (note: the question relates to reversing the flow through the filter so this "outlet" is really the inlet as designed).

 

Will it clean dirt and dust from the fuel - yes.

Will it clear water droplets - up to a point probably yes but at a much reduces service life.

Will a glass/plastic bowl or the drain tap ever show ann water - almost certainly no.

 

Is that the filter manufacturer or the engine manufacturer? If you look at the photos that RLWP posted on the previous page you can work out from the arrows which way CAV designed it.

 

 

 

 

I think that you have this wrong. Pleated filters will store both muck and water in the bowl. pocket filter will store water in the bowl and muck in the filter pockets.

I imagined, obviously incorrectly, that the minute droplets of water caught on the filter surface would, with time, get larger and fall off, but remain on the 'dirty' side, but you are saying that once large enough, they push through the filter to the 'clean' side. That certainly would explain the recommended flow direction.

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36 minutes ago, Bargebuilder said:

I imagined, obviously incorrectly, that the minute droplets of water caught on the filter surface would, with time, get larger and fall off, but remain on the 'dirty' side, but you are saying that once large enough, they push through the filter to the 'clean' side. That certainly would explain the recommended flow direction.

 

FWIW I thought that at first, and it needed a fair bit of research to find out that was not the way they work. I THINK a pleated element may be more amenable to work in reverse. When I tried t discuss using their pleated filter in pocket filter and discuss their relative efficiency with a Filtre Auto technical chap he did not want to discuss the relative efficiencies and just said "we have had no problems". Make what you will of that but I always seek a pocket filter for diesel.

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1 minute ago, Tony Brooks said:

 

FWIW I thought that at first, and it needed a fair bit of research to find out that was not the way they work. I THINK a pleated element may be more amenable to work in reverse. When I tried t discuss using their pleated filter in pocket filter and discuss their relative efficiency with a Filtre Auto technical chap he did not want to discuss the relative efficiencies and just said "we have had no problems". Make what you will of that but I always seek a pocket filter for diesel.

I am impressed with your depth of knowledge and deep interest in the subject. Thanks for being so generous with your expertise.

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