RAW WATER EXPERT WANTED

[martynwhiteley]

I recently purchased a Birchwood 27 with twin BMW B130 petrols on legs.

Despite a new Johnson pump and hoses on one engine, a new impellor on the other and many hours bent double in a micro sized engine room, they are both very reluctant to prime and pump raw water.

The inlet comes from the leg, through a vetus strainer, and then the direct drive Johnson pump on the end of the cam. The boat had been out of the water unused for a few months.

After suspecting a blocked inlet, I tried pumping from a bucket in the bilge. The new pump did prime eventually at about 5000 rpm, but fails to repeat this very often when reconnected to the leg inlet. However water will flow back out from the strainer through the leg inlet ok. There does not appear to be any air leaks.

The other engine ran ok for a couple of hours, but now struggles to prime.

Any advice?

Also, could the leg inlet be replaced by sea-cocks or would this affect leg cooling?

Plus, could some back pressure in the system be causing the problem?

Please save my sanity!

 

[rich]

I had the same problem with my volvos on last boat, i cured it by refaceing the impeller pump flange and cover.

rich )

 

[Guest]

Maybe the impellor is adjusted incorrectly or you maybe airlocked, possibly some kind of bleed off in the line may help you. (I don't want to mention the possibility of head gaskets)

Bally Bollinger Boundah

 

[Guest]

Try pressure testing your cooling system to eliminate air leaks

Bally Bollinger Boundah

 

[mtb]

Re: Check this lot

Well if there are no leaks , the impellers are not old and hard, don't forget the rubber will harden with age just because it's new don't mean it's not sat on a shelf for some time. As already said the body of the pump and squash plate / cam is ok .Oh and what about the seals sometimes air can be drawn through.As you have renewed one the actual shaft should be fine old ones can get worn at the point the seal run's.
Head of water
Most pumps will draw with out problem's
Are your legs deep enough when under way to allow sufficient ingress of water .

What about fitting a header tank a small one with a line to both feed inlets this way you will have water from the start cos it does not take long to wear out an impeller.
The only thing to do is put a tap in line so once your running you can turn off the tank.
Yes it's a pain to fit a tank but if every thing else is ok then it might be the only way.
Cheers
Mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler or tug v, cheap or swap for tug

 

[glmuse]

See if the pump works by bypassing the raw water strainer (joining up the two rubber hoses with a piece of pipe), this will at least eliminate whether the strainer is at fault, or try fitting two hoses directly to the suction and outlet of the raw water pump, to see if the pump actually pumps water.

Cliff Muse

Geraldine

 

[Mirelle]

May a sailing man offer a suggestion?

How high above the waterline are the Vetus strainers? These gadgets are notorious for drawing air in, and the makers say they should be just six inches above the waterline. With mine, when the strainer was 18" above w/l, the pump would hardly draw any water at all.

Using about a pound of Vaseline on their sealing surfaces also helps a bit - but the height is the great issue.

 

[coliholic]

I had a Mirage with AQAD 30's on legs and on one occasion when I cleaned the raw water filter, I forgot to put the sealing cap back on top of the filter, before putting the screw cap on the Vetus filter. Result was air was getting in and the pump, didn't. Does your filter have this cap that goes on top of the strainer? Or just an "O" ring that creates the seal. Maybe the O ring's missing?

Harder to describe than to see, so have a look at the Vetus site, you can just make out the O ring on the cutaway drawing bottom right in this piccie, http://www.vetus.com/frame-sea.htm.

Or if that link doesn't work, www.vetus.com, then select Filters - water and click on the one you've got for an exploded pic.

Or alternatively is the cap cracked and hence leaking air? Or a bit crudded up and not tightening down enough?

Either way to me it sounds as if air's getting in somewhere.

Assuming you did put the woodruff key back in the drive shaft when you changed the impellors on the pumps. And new gasket on the pump\impellor cover.

 

[martynwhiteley]

Latest Update

Here is the latest:-

After bypassing the Vetus strainer on the stb engine, it looked there was enough water being pumped through a new see-through hose fitted direct from the leg fitting to the pump inlet.

I ran the engine in the river for 15-20 minutes, but the temp still climbed to 95 deg and rising. I was just about to switch off, but noticed steam rising from the inlet water hose where it meets the leg connection. The hose felt 'red hot', and infact closer investigation showed the hose to have collapsed near to the pump inlet, despite being reinforced (obv. due to heat).

The only explanation was hot exhaust gas/water was getting striaght back up the inlet. I quickly arranged for a lift-out, suspecting both inlet and exhaust flexibles had ruptured within the leg case.

On investigation, the inlet was indeed split, but the exhaust seems intact. It would appear that the cavity in the leg where these hoses run was acting like a heat exchanger, fuelled not only by the exhaust flexible, but by two 'idle relief' holes pushing a hot gas/water mix directly at the split in the inlet hose.

Now waiting for new hoses to arrive!!!!!