Volvo 2030 - raw water pump / syphon break help please

[StevenJMorgan]

Ironically after reading recent threads on here about how 2030's eat impellors (and after thinking how mine didn't) my engine alarm went off last time I took my boat out. I took the cover off the pump - vane missing replaced impellor and found the missing vane at the top of the pump outlet pipe where it enters a syphon break.

All is fine now on the engine cooling side but I now have something strange happening with the syphon break. My raw water cooling side is set up as follows ; seacock to strainer, strainer to inlet side of pump, outlet side of pump to syphon break and then to engine (i think). The syphon break is mounted up high and has a third small diameter pipe running from it to the bilges. I always assumed that this was the 'overflow' pipe and that this would allow any water backing up to be discharged into the bilge rather than into the cylinder head. In normal operation prior to replacing the impellor no water flowed out of the end of this pipe. Now however since the distruction of the old impellor and replacing with a new one there is a constant drip from this overflow pipe even when ticking over on marina berth. Does anyone have any ideas why this would be happening? I have suspected that a small piece of rubber from the old impellor could be blocking something but when I matched up the vane to the impellor I seemed to have found all the bits.

Any help much appreciated. I may not get back to a computer for 24 hrs so thanks in advance for any help. steve

 

[phatton]

Steve,

I recently had a similar problem. I had a leak after the engine alarm went off. I found the waterpump bearing had gone and resulted in a leak. Though your leak may be different.

Its a difficult job to replace the water pump bearings if you don't have the right tools and manual. I bought a reconditioned pump from RK Marine in Bursledon and had it fitted an easy job. No leaks now though will be constantly checking impellors..

Phil.

 

[boatbuilder]

Siphon breaks have a habit of sticking open or closed, due to salt water drying and crystals forming. Take it to bits and clean all the bits in fresh water. This usually cures it.

 

[Lakesailor]

Not as in Fitzpatrick-Morgan?

(Shut up the rest of you, it's not the punchline to a joke.)

 

[branko]

Everybody with Volvo Penta motors have similar problems.As I know , most of us solve this problem on the way that we buy longer thin tube from siphon and connect it on back outlet. I have bought white plastic outlet, bore a hole back over stairs and forget leaking.

 

[boatbuilder]

who , or what is Fitzpatrick-Morgan ? I thought this forum was about boats

 

[Ships_Cat]

As Boatbuilder has said a clean out often cures the problem.

I have been told that a reason that they tend to dribble on a wet exhaust engine is that the exhaust pulses can feed back from the injection point through the water in the engine's exchanger or water jacket (if raw water cooled). I think there is some validity in that as we have two siphon breaks on ours (one is on the water takeoff for the shaft gland) and one periodically dribbles and the other (taken off further away from the exhaust, plus on a hose of much larger diameter) does not. When it dribbles, it only does so at certain engine revs, which again points to a pulsing feedback from the exhaust injection point.

What may have happened in your case (assuming a wet exhaust) is the the new impellor has changed the flow characteristics through the engine water jacket or exchanger allowing more feedback of the exhaust pulses at the frequency critical to the antisiphon valve. I suspect, but don't know, that an engine with an exchanger would be more susceptable to this due to the more direct water path.

If the valve is a simple rubber duck bill type one, a very thin film of petroleum jelly on the inside sealing lips of the valve sometimes helps (but must make sure it does not make it stick closed). When ours goes through a dribbling stage of its life, I usually just put a small container under it.

John

 

[Lakesailor]

I hope your comment was in jest

 

[boatbuilder]

I'm afraid that you have lost me completely,its not in jest but confusion.

 

[boatmike]

I think all that has happened here Steve is that replacing the impellor has restored full pressure and made the leak more noticable. It's worth noting though that there are two types of antisyphon devices. Those that have valves and can as others have said stick open or closed, and those without. Those without need a tiddly little skin fitting to constantly discharge overboard. (Those with a valve don't of course.) The biggest risk is those with valves can stick closed and you can wreck your engine with a hydraulic lock on start up. For this reason I always prefer to fit one without a valve. Whenever I have inherited a boat with a valve dependent antisyphon tube I have always taken the valve out and led the end of the tube overboard with a 1/8 inch skin fitting above the WL next to the exhaust outlet. That way it can't jam and wreck your engine!