Do I need a Pre-Filter?

[JimC]

My boat just has a water-separator between the fuel tank and the engine

Each year I drain off any water (there never seems to be any) and change the engine-mounted filter on the Yanmar 2GM20, a simple job.
My previous boat had a CAV combined water separator & filter and I changed its element (messily) every year, usually leaving the engine-mounted filter in the Bukh in situ.

My question is: should I really have a pre-filter in the fuel line? There isn't enough depth to replace the existing water separator with a combined CAV filter & separator but I could leave the existing separator in situ and fit a stand-alone filter in the line closer to the engine. I would use one of the spin-on CAV replacements sold by ASAP supplies but I wonder is it necessary, I always carry several spare filters for the Yanmar and don't want to add needless complexity.

 

[sailorman]

My boat just has a water-separator between the fuel tank and the engine

Each year I drain off any water (there never seems to be any) and change the engine-mounted filter on the Yanmar 2GM20, a simple job.
My previous boat had a CAV combined water separator and I changed its element (messily) every year, usually leaving the engine-mounted filter in the Bukh in situ.

My question is: should I really have a pre-filter in the fuel line? There isn't enough depth to replace the existing water separator with a combined CAV filter & separator but I could leave the existing separator in situ and fit a stand-alone filter in the line closer to the engine. I would use one of the spin-on CAV replacements sold by ASAP supplies but I wonder is it necessary, I always carry several spare filters for the Yanmar and don't want to add needless complexity.

i have the same set up as you, it works for me

 

[nigelmercier]

That looks quite like my fuel pre-filter, are you sure there isn't meant to be a filter in there

 

[sailorman]

That looks quite like my fuel pre-filter, are you sure there isn't meant to be a filter in there

mine is just the glass bowl water trap

 

[JimC]

That looks quite like my fuel pre-filter, are you sure there isn't meant to be a filter in there

I don't think so. I believe the upper part of the unit above the metal bowl contains something called an agglomerator but I don't understand its purpose.

 

[sailorman]

I don't think so. I believe the upper part of the unit above the metal bowl contains something called an agglomerator but I don't understand its purpose.

• AGGLOMERATOR (noun)
The noun AGGLOMERATOR has 1 sense:

1. a device that causes material to gather into rounded balls

 

[pelissima]

I have the same and have added this
http://www.diadromi.com.gr/index.php?act=viewProd&productId=5612
(pls disregard the language, just see picture)
As you can see it has a grid inside,it costs 1.5 euro and I can see if there is any sludge sign.
This way I monitor when it is time to clean the tank

 

[sailorman]

I have the same and have added this
http://www.diadromi.com.gr/index.php?act=viewProd&productId=5612
(pls disregard the language, just see picture)
As you can see it has a grid inside,it costs 1.5 euro and I can see if there is any sludge sign.
This way I monitor when it is time to clean the tank

i have one of those on my heater but the flow rate would be on the low side for a larger engine

 

[david_bagshaw]

I don't think so. I believe the upper part of the unit above the metal bowl contains something called an agglomerator but I don't understand its purpose.

It is too slow the flow of the fuel to allow small water beads and small particles of dirt to gather together and form a droplet, that then is large enough to fall to the bottom, rather than be swept past towards the engine.

 

[noelex]

I would fit a proper primary fuel filter.
Clean fuel is vital for a diesel and the dual filtration of a coarser primary filter and finer secondary filter is superior to only a single filter.
It also provides a much longer running time if you do have some dirty fuel or diesel bug problem.
Cheap insurance.

 

[JimC]

I don't think so. I believe the upper part of the unit above the metal bowl contains something called an agglomerator but I don't understand its purpose.

Following further study of the CAV manual http://www.fujiyachts.net/manuals/CAV%20Diesel%20Fuel%20Filter.pdf I now realise that what's in the body of the unit above the bowl is a sedimenter not an agglomerator. This seems to consist of a cone over which the fuel disperses itself as a thin film.

 

[sailorman]

Following further study of the CAV manual http://www.fujiyachts.net/manuals/CAV%20Diesel%20Fuel%20Filter.pdf I now realise that what's in the body of the unit above the bowl is a sedimenter not an agglomerator. This seems to consist of a cone over which the fuel disperses itself as a thin film.

what you have is quite adequate

 

[ridgy]

If your engine filter is readily accessible then leave it at that. Mine is hard to get to and I didn't fancy having to change it at sea so I put in a CAV filter at the front. Also CAV filters cost £1 something whereas the engine filter is £15 a time.

 

[pathfinderstu]

• AGGLOMERATOR (noun)
The noun AGGLOMERATOR has 1 sense:

1. a device that causes material to gather into rounded balls

that could be what this forum is called at times then ..lol

 

[fien397]

IMHO The current arrangement you have is sufficient for a small engine. If you want a bit of extra reassurance then clean your tank out, and always use a filter funnel for refuels. Prevention is better than cure and if your tank is full of cr*p then almost any standard filter arrangement will block eventually, typically when your motoring in bad weather, when you really don't want it to. Also if your getting much water in your separator, might be worth checking the O-ring on your deck filler or changing fuel supplier.

 

[JimC]

Thanks for all replies. I'll leave things as they are and follow the suggestions for fuel cleanliness etc.

 

[Slowtack]

I have a sedimeter/agglomerator/whatever unit like yours followed by a CAV filter with bowl followed by the engine spin on filter. So far so good- the sedimenter takes care of most of the dirt. Very little reaches the engine filter. Still need to clean the tank every few years though.