Air in Raw Water Filter

[WestWittering]

Has anyone experienced problems with this? After sailing on a starboard tack, the water seems to drain from the bowl, so when I start the engine, it either takes an age to draw water through or won't draw at all - like on Sunday.

To run the engine, I had to loosen the front plate on the pump to bleed the air through and fill up with water. The top of the filter bowl is worn & doesn't seal properly, but I can get it to 99% seal. Is it just a question of a completely new filter, re-siting the intake skin fitting or do I need an anti-syphon of some sort.

The previous owner fitted a new pump as he had problems, so it is kind of on going. I would like to sort this as it does get a bit stressful and the last impeller I took out was in bits - it has a new impeller & gasket now, always pumps on start up, but it is just after sailing that we get this problem.

Di

 

[Tranona]

The slightest air leak will cause the symptoms you describe. Find out why it is not sealing. Maybe just needs a new O ring but if the top or housing has crack or the threads are worn so it does not come down tight probably time for a new filter. Also double check the hose connections because these can also cause leaks

 

[WestWittering]

Thank you - fitting a new filter is also the easiest solution!

Di

 

[VicS]

Thank you - fitting a new filter is also the easiest solution!

Di

Maybe caused by air finding its way up the inlet esp if its fitted to the starboard side of central and it only happens on starboard tack.

You could try shutting the inlet seacock to see if that stops it happening.

 

[Rossynant]

So would I suspect. Water draining out from intake placed too high or too much out of the side. Moving intake to better place, down or to the center (or even forward) may be the solution. But then may not, if this is flat bottom boat...
Or you may use some other place and check; on some boat the intake was T-ed from cockpit drain outlet, for instance. Not that I would recommend, but simple solution for a moment or for trying, if there is some better intake already.

Another thing - strainer (that is filter you call it) itself. I presume the water strainer/filter is above the waterline - then indeed, water will drain off if not airtight. Maybe start with buying new, if the one you have is this cheap plastic bowl kind. It's a dispensable Then you will see, and good idea to have a good one anyway.

Still possible to purchase a solid, tight metal strainers, meant to be placed under water level. These will not drain off, nor make the pump struggling to suck water in - and quite possible that your boat was designed to have such one there.
So that is another solution, alternative to moving the inlet, maybe less trouble - buy yourself a proper kind of strainer.
Something of this kind (I have similar) http://www.youngsboatyard.co.uk/media/productimages/409_main.jpg
or in case you like the show: http://www.go2marine.com/docs/1/1/2/9/112963F-p.jpg

 

[vyv_cox]

We have had exactly the same problem, not necessarily only on starboard tack but in any boisterous conditions in which the inlet skin fitting might be above the surface of the water. The engine is a Yanmar 3GM30F, originally with a combined skin fitting, seacock and strainer but later with a skin fitting and seacock and a Vetus strainer about 200 mm above the waterline. The problem occurred with both arrangements.

My first action was to add a non-return valve close to the original seacock. This had no effect. Whenever the problem occurred I would remove the hose from the pump, close the seacock, back-fill the hose with water and replace it, open the seacock and immediately start the engine. This was usually successful.

I then installed the Vetus strainer above the waterline but the problem continued. It was easier to overcome, by removing the strainer lid and filling it with water. The strainer was new, with a greased O-ring, making air leaks most unlikely. I checked that the pump internals were not badly worn, re-faced its cover, which was a little, but these measures were not successful, so I put up with the problem.

Then the lip seal on the pump shaft failed, leaking water at a high rate. I replaced the seal and the problem has never recurred since. That was in 2008. I assume that air was able to leak in when the engine was off, allowing water to run from the seacock.

 

[Otter]

It's an odd phenomenon, we have a vetus water strainer well above the waterline that always has air in it. I've filled it a few times but after running the engine a while it is full of air, sitting at the top of the loop, about 5 feet above the inlet and 2 feet above the engine. It never fails to pull water through and trying to get the damn lid off confirms there is no way air is getting in there! Maybe there's a small leak in the sea water side but I've never seen any drips or signs of them. I have no idea ow the air gets there or why it's never more than the volume of the strainer - leave the boat a day, week or a month and it's the same.

 

[Rossynant]

Exactly - and moreover we don't know how the piping goes in OP's boat.
If he drains the pipes dry then air will be there, no matter what. Maybe he will show how it is organized there.
But on flat bottom boats this is not such a rare problem; good way of dealing with it is to have intake pipe going from low down, flat on bottom - no upward loops - slightly upward to get the highest at pump. So when boat is 'back in water' - water comes in, air gets up and out, and pump has the water, or at least has a good chance. Those vertical strainers mounted at bottom have outlet low down and allow water into pipe the moment they sit back in water.

May I be so rude as to add I would not put this kind of strainer: http://www.vetus-shop.com/images/FTR140.png on modern flat boat? This is for boat floating so much down in water that you have to take the strainer well up to reach waterline. No wonder it's connections are from down under. But this is not proper way. Such things you may have in house supply line. (I have not, got myself a vertical kind filter... )
And naturally this will result in a kind of siphon loop, keeping the air in it. Nothing wrong with a bit of air inside, as long as the water level is still inside the bowl, about half high.
But once you drain such a loop, how could water get in?

Vertical drainer on bottom.
You still have the cover above water, so to open it in case of need, but it's full of water above the pipe to pump - since the air can escape toward the engine, at least up to the pipe level.

For a strainer placed high above hull inlet - look at this one http://www.go2marine.com/docs/1/1/2/9/112963F-p.jpg
it has the pipe outlet (to engine) practically on top. Once again - the air will escape, get up from it.

 

[pampas]

I put a "Ping pong" ball in mine so I could see if the pump is working also greased threads and both sides of the seal. Personally I would go this method first before drilling any more holes.

 

[david_bagshaw]

On our lazarette generator, (7.5 Kva onan, )I fitted an up-stand to the inlet in the filter bowl, which is well above the waterline, so there is always some water quickly available on starting the engine.

This stops the bowl draining out, and along with a horizontal section to the intake port of the pump, whatever drains out from the pump, is quickly replaced.

 

[WestWittering]

Thank you very much for all your replies - much appreciated. In my minds eye, the strainer is about water level as it is mounted on a wooden block attached to one of the quarter bunk supports. It is a small plastic vetus, what I wasn't sure of was how water/air tight the strainer had to be. I have bought a replacement, a slightly newer design - still a plastic Vetus though but I was put off fitting it as it involves a bit of woodwork & pipe work surgery and I am a girl. I don't mind doing it if that is the fault, but I didn't want to struggle with it & make it worse. The intake is vertical, though as the strainer is approx 10 inches from the port side and she is quite flattish, this could mean that the skin fitting is not as low as it could be. I think I'll fit the new strainer, test drive and if it is not cured, move the whole shebang towards the engine so the skin fitting can be moved more to the centre. Can I just ask though, does the pipe work to the water pump have to be horizontal as it is at the moment or would a small incline be okay OR shall I just get the instructions?

On the credit side, I did do three other small jobs today & have got the parts for a couple of other things.

Di

PS it is a centaur we are dealing with, so not much space to muck around with. Photos tommorow - snow permitting.

 

[ianat182]

You could start by ensuring that you don't have an air leak through the lid of the strainer; check the O ring if fitted and liberally grease with Vaseline or similar. This will have two benefits, it will be easy to unscrew and check for weed/clean ,and eliminate an air leak.

I have the Westerly Tiger with a Volvo engine and the installation instructions for my water filter are to mount 200 mm above the waterline level. To establish this detach the inlet pipe from the filter and raise the end until the water will not flow out; note this height on the bulkhead and refit pipe and lid to the filter; remount the filter 200mm above the mark on the bulkhead, reconnect the pipe and start the engine. There should be ample water drawn up to the filter but this may drop to the 100mm level and the chamber appear empty, this is normal at rest. Most of the Vetus I've seen all have a vertical intake to the filter bowl,as does my own which replaced a very large old bronze unit at waterlevel that was originally fitted. Provided the pump/impeller is in good shape you should have no trouble drawing raw water the 100mm needed to fill the bowl.
Depending upon the size engine you have you may need a larger Vetus unit with an increased flow rate,they are all the same price but the hose diameters vary for each from 3/4" for the (19.1mm inside diameter) to 1" O/D (25.4mm i/d) 1 1/4"(31.8mm i/d) these give flow rates of 26 glns/min;46 glns min; and 72 glns min respectively. Prices from the F4 chandlery catalogue was £85.95 a non Vetus variant for all the sizes mentioned is £24.56.
I have fitted the latter type with no problems,same fittings and hoses used.


ianat182

 

[Blueboatman]

I am sure you have enough, comprehensive answers already, so this is an ' extra' sort of suggestion..
If ever you were contemplating fitting a seawater galley tap, a very good place to T off from for the supply hose would be between the engine water filter unit and the engine water pump, as mine own is..
By pumping the seawater foot pump you can eject any air v quickly .
This is not a 'solution' but it is a useful ' bonus feature' handy for priming when say fitting a new impeller or indeed, dealing with mystery air leaks quickly...

 

[LittleSister]

If ever you were contemplating fitting a seawater galley tap, a very good place to T off from for the supply hose would be between the engine water filter unit and the engine water pump, as mine own is..
By pumping the seawater foot pump you can eject any air v quickly .
This is not a 'solution' but it is a useful ' bonus feature' handy for priming when say fitting a new impeller or indeed, dealing with mystery air leaks quickly...

But doesn't this also introduce more potential air leaks into the system?