Problem with my water!

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billy the red

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tutak-ii.blogspot.co.uk
Greetings,

I wonder if there is anyone out there who has experienced a similar problem.

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My little Fisher 25 has a raw water cooled Bukh 20. Runs just fine for days at a time in relatively flat water, i.e. less than 2 metre waves. But when it starts to popple up a bit it stops pumping water and the overheat alarm comes on. To remedy I take off the water pipe to the injection elbow and run until the water starts to pump again and reconnect. Fine until we get another big wave rolling under us and it will do it again. Doesn't do it all the time and I never no when it will happen.

The pump has been changed for a new one, just to make sure. All the water pipe work has been changed. The anti-syphon has been removed (temporarily) and all the pipework made as short as possible. The injection elbow is clear and the exhaust is fine. Thermostat and engine galleries are clear and working. The seacock is a ball valve with a long fisherman's filter. The exhaust outlet is on the waterline.

What is going on? Possibly air getting into the strainer. Big waves up the chuff causing back pressure stopping the water injection happening together with a slug of air. I really haven't a clue as it never used to do it.

I'm just starting to get a little nervous when I go out now and I'm pretty fed up too.
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Any thoughts would be most appreciated, thanks.

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tutak-ii.blogspot.com/
 
Sounds like maybe an airlock with an impeller that isn't capable of pulling the water through. Check the impeller but also check the housing to see if it's worn. How long and high is the run of pipe from seacock to pump?
 
When I had one of these engines and when checking the water pump impeller I would also ensure that the impeller cover was smooth on the inside, by rubbing it over some 120 grit emery cloth stuck to something flat. Before I did this the efficiency of the pump was very much reduced because it lost pressure around the sides of the impeller blades caused by circular grooves (worn by previous impellers). If it had to overcome much back pressure (perhaps yours caused by the following sea) then a new impeller was not enough. I think I found this out when comparing the old cover with a new one; the only difference was the grooves.

Also, check your thermostat; is it working properly?
 
Depending on where the water intake is, could it be the troughs causing a problem, rather than the crests? Could the pump be sucking in air in the troughs?
 
oldfatgit said:
When I had one of these engines and when checking the water pump impeller I would also ensure that the impeller cover was smooth on the inside, by rubbing it over some 120 grit emery cloth stuck to something flat. Before I did this the efficiency of the pump was very much reduced because it lost pressure around the sides of the impeller blades caused by circular grooves (worn by previous impellers). If it had to overcome much back pressure (perhaps yours caused by the following sea) then a new impeller was not enough. I think I found this out when comparing the old cover with a new one; the only difference was the grooves.

Also, check your thermostat; is it working properly?
Click to expand...

check the "wear" plate in the back of the pump, that might have grooves worn into it
 
I cannot explain the symptoms you describe but it would be well worth checking the fitting beneath the flywheel where water is injected into the engine. It is possible to remove this without removing the flywheel but you may need to adapt an Allen key to do it. This fitting, like an old-fashioned gas poker, tends to become fouled up with calcium salts. Blockage would cause the overheating but not the absence of flow, as all the seawater would be diverted to the bypass.
 
We get similar problems with ours after fitting a feed to a deep sea seal (no problems prior). Since, the post below, we have raised the anti-siphon valve another 150mm and the problem has been reduced but not cured. Now the raw water filter drains to within a couple of mm of empty -- just enough to maintain flow in an emergency -- we still have to top up though.

We're beginning to think it's maybe an air leak somewhere!?

See our post "Water lubricated stern deep sea seals" http://www.ybw.com/forums/showthread.php?t=285697
 
GandJ said:
We get similar problems with ours after fitting a feed to a deep sea seal (no problems prior). Since, the post below, we have raised the anti-siphon valve another 150mm and the problem has been reduced but not cured. Now the raw water filter drains to within a couple of mm of empty -- just enough to maintain flow in an emergency -- we still have to top up though.

We're beginning to think it's maybe an air leak somewhere!?

See our post "Water lubricated stern deep sea seals" http://www.ybw.com/forums/showthread.php?t=285697
Click to expand...

if its a vetus type ( some cheap carp out there ) why not add a smear of petroleum jelly to the seal to the lid
 
GandJ said:
We get similar problems with ours after fitting a feed to a deep sea seal (no problems prior). Since, the post below, we have raised the anti-siphon valve another 150mm and the problem has been reduced but not cured. Now the raw water filter drains to within a couple of mm of empty -- just enough to maintain flow in an emergency -- we still have to top up though.

We're beginning to think it's maybe an air leak somewhere!?

See our post "Water lubricated stern deep sea seals" http://www.ybw.com/forums/showthread.php?t=285697
Click to expand...

The only way the raw water filter can drain to empty is if water is passing the pump. This suggests that the impeller does not fit the cavity, due to wear of either the front plate or the rear of the casing. This could be due to scores or general wear, or even that the wrong impeller has been fitted.

This is not the OP's problem as he says he has fitted a new pump.
 
+1 I had exactly the same problem with a Buhk DV20 in a Southerly 95 and it was due to wear in he pump as described already.

The S95 has a very shallow hull and inlet is close to the surface. It doesn't take much of a heel to allow it to suck air. The worn pump doesn't pump air well enough to get water flow back again.

Perhaps the OP meant "fitted a new impeller" when he said "pump changed for a new one". In that case it is almost certainly wear in rear and/or front part of pump. If not, I can't see an obvious reason.
 
We have also experienced priming failure due to worn pump seals but in the Bukh, in the installation shown by the OP, this would show up as seawater leaking from the strainer through the pump telltale holes into the bilge (or into the engine :eek:) I am assuming that this would have been noticed.
 
vyv_cox said:
We have also experienced priming failure due to worn pump seals but in the Bukh, in the installation shown by the OP, this would show up as seawater leaking from the strainer through the pump telltale holes into the bilge (or into the engine :eek:) I am assuming that this would have been noticed.
Click to expand...

Perhaps not, I don't remember seeing any leak when I had the problem. I suppose it is possible for the seal to pass air in but stop water coming out .

I used to check the holes in the pump drive tube from time to time and put a tissue under/around it 1-2 times each year to check for oil or water leaks. So I would remember a leak if I'd had one.
 
billy the red said:
Greetings,

I wonder if there is anyone out there who has experienced a similar problem.

scan00062-Copy.jpg


My little Fisher 25 has a raw water cooled Bukh 20. Runs just fine for days at a time in relatively flat water, i.e. less than 2 metre waves. But when it starts to popple up a bit it stops pumping water and the overheat alarm comes on. To remedy I take off the water pipe to the injection elbow and run until the water starts to pump again and reconnect. Fine until we get another big wave rolling under us and it will do it again. Doesn't do it all the time and I never no when it will happen.

The pump has been changed for a new one, just to make sure. All the water pipe work has been changed. The anti-syphon has been removed (temporarily) and all the pipework made as short as possible. The injection elbow is clear and the exhaust is fine. Thermostat and engine galleries are clear and working. The seacock is a ball valve with a long fisherman's filter. The exhaust outlet is on the waterline.

What is going on? Possibly air getting into the strainer. Big waves up the chuff causing back pressure stopping the water injection happening together with a slug of air. I really haven't a clue as it never used to do it.

I'm just starting to get a little nervous when I go out now and I'm pretty fed up too. /
Click to expand...


Was the anti syphon loop between the sea inlet and the pump????? It should be after the pump between the pump and engine or in the line to the mixing elbow. If in the wrong place it can affect the priming of the pump.
 
Just like to say thanks to all replies and suggestions and apologise for not replying earlier. I was in the middle of changing my email address and the site did not let me back in for a long time. Hey.


billy the red
 
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