CAV water separator drainage

[FairweatherDave]

In my quest to introduce problems into a well functioning system I thought I would drain a little fuel from underneath the cav water separator fuel filter to check for any water (the glass bowl diesel looked fine to me). Unscrewed the little plug and pretty sure air was being pulled in, saw a few bubbles, but nothing came out. I think the beta 25 self primes and the air won't be a problem but curious if anyone else has had a similar experience?

 

[Daydream believer]

Poke a wire up the hole it could be a bit of gunge blocking the hole. I have had something like that, so changed the filter as there was evidence of diesel bug. A good dose of treatment was applied & no further issues

 

[FairweatherDave]

Hmm. I did get one drop out but a poke with a wire might be a good idea. I have subsequently found an old thread suggesting a good idea to create a bit of "head" in the Tank by filling it. It's quite low. But that should wait for the start of the season for maximum longevity of the fuel ?. And of course I should be changing the primary filter anyway...this was just me fiddling about after I had drained a sample of fuel from the tap under the tank.

 

[superheat6k]

If the filter drain is above the fuel level then the pressure within will be below atmospheric I.e. a partial vacuum, hence to drain the filter some air must enter first, unless there is a means of creating a partial pressure.

On my last oat I used the portable fuel polishing pump to create such a pressure along the pickup line for filter priming and if necessary draining. This was also useful for clearing away a slug of crud fouling the fuel pickup. Although with regular polishing plus heavily greased filler cap threads I kept the fuel perfectly dry and hence bug free.

I have just installed a plumbed in fuel polishing system on my new boat, with a flexi hose connection that I can use to pre fill my Racors, and I might add some priming connections to each engine filter unit, but only if I suffer pick up problems.

I do suspect each tank has a 32 year accumulated layer of crud just below the fuel take off point and I am thinking about whether I need to drain each tank and properly clean the base level, but even with decent size access ports on the side of each tank, access is not to clever so this would be quite a task.

 

[LONG_KEELER]

In my quest to introduce problems into a well functioning system I thought I would drain a little fuel from underneath the cav water separator fuel filter to check for any water (the glass bowl diesel looked fine to me). Unscrewed the little plug and pretty sure air was being pulled in, saw a few bubbles, but nothing came out. I think the beta 25 self primes and the air won't be a problem but curious if anyone else has had a similar experience?

I don't know much about these things, but in a recent thread it was suggested that water would not be seen in a CAV filter due to the ethanol holding it. When I had diesel engines , even without ethanol added , I never did see any water in the filter. On one occasion I managed to remove a stainless tank for inspection. It was unbelievable how much crud was in there. I'm sure a decent sized drain plug would help to annually drain some of it out rather than just water.

 

[Stemar]

My fuel filters (twin engines, one per hull) are just about the highest point in the system. When I changed the cartridges, I fitted these

between the tank and the filter because I couldn't see any way to bleed the system without. A mechanic told me the only way to do it was to hand pump the engine lift pump to suck the fuel through, which sounds like hard work.