Should I fit a non return valve in my cooling line???????

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MarkyR

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Well what can I say? I have tried everything and I am still having problems with my cooling on my Yanmar 15hp 2QM.
In a nutshell? when I have been sailing, I have problems with the water not pumping around the engine. I have replaced the impellor,seacock and fitted a remote filter. It would appear that an air lock is being created and the water is being syphoned out of the waterpump as I sail along. Only after I stop the boat and wait will water start to pump out again. Never happens under engine only. I have thought about fitting a non return valve between the inlet and waterpump to stop water being drawn out through the seacock. Any suggestions or advice? Not sure where else to go from here.
Thanks.
 
Hi

I had a similar problem with my old Volvo. Mine would pickup water when started in the marina, but after a sail it would fail to prime. Mine was caused by a worn pump body. The impeller sides and edges need to be in contact with the pump for it to "self prime". Is the inside of the pump cover worn? You could try turning the cover round, this might help. I eventually bought a new pump and it solved the problem.
 
A flexible vane type of pump should prime upto a height of a couple of feet or more. If it does not then, having replaced the impeller the problem must be the result of a worn pump body, wearplate or end plate. Check the end plate for wear and the wear plate if it has one. Cam plate as well for that matter.

A non return valve somewhere, close to the inlet I would suggest, may well overcome the problem but at the end of the day the pump performance is going to be down if it is worn and it will only get worse.
 
I had exactly your problem on my VP 2030. I solved it this year by fitting a non return valve just before the Vetus anti syphon valve. It works perfectly. Bought mine from RSS - cost about£7 and fitted in a few minutes. Before that I had moved the position of the sea water filter, got a speed seal but nothing stopped the water being sucked out when sailing. The only alternative is to close the sea water cock when you start sailing but mine is not easy to get at. Best of luck.
 
[ QUOTE ]
I solved it this year by fitting a non return valve just before the Vetus anti syphon valve.

[/ QUOTE ] Does that mean you have the antisiphon valve between the inlet and the pump?
That will cause problems. It would cause exactly the problems described!
It should either be after the pump or between engine outlet and exhaust injection. Preferably the latter.
 
No! I have the inlet from the saildrive to the sea water filter, from there to the pump and from there to the non return valve and from there (1") to the flow switch and from there (2") to the Vetus anti syphon valve. From there to the heat exchanger inlet. I was concerned that having it so high would affect the anti syphon but I have clear pipes and you can see the Vetus drain the water almost instantly into the heat exchanger. If you like I will post a picture. The flow switch was before I had the non return valve. It now goes off instantaneously. Before the non return valve was installed you could see the water level stable just above the pump after the engine was switched off. As you sailed it just dissapeared. I think this happens to lots of boats but VP when challenged say that the pump is capable of priming itself. It may when new but mine has now done 900 hrs. I now lots of people with new pumps that have to wait sometimes minutes for the pump to prime.
 
That's fair enough.
MarkyR's intention is to put a NRV between inlet and pump (he has a strainer integral with the inlet seacock and a very short direct run to the pump IIRC) When you said you had the same problem and solved it with a NRV before the antisiphon valve it produced a picture in my mind of inlet, NRV, antisiphon valve, pump!

I think in your situation I would have put the NRV on the suction side of the pump and as close to the inlet as possible, before the stainer even if feasible, as that would trap the maximum amount of water in the system and allow the minimum amount of air to enter via the inlet. However if what you have done solves the problem for you that's fine.
 
The problem for the OP, assuming the pump is not worn could be a slight leak in the hose to or from the strainer. I had this and was baffled for a long time because all the clips were tight. However, one had corroded and although appeared to be tight was not allowing air in and water to flow back out through the skin fitting. New Jubilee clip, problem solved.
 
I don't think it matters where in the circuit it is situated, as long as it is before the anti syphon valve. If it stops the water retreating down the pipe, because nature doesn't like a vacuum, then it serves its purpose. My sea water pipe is always full up to the antisyphon valve and that is the best possible solution. The NRV may need cleaning, I don't know yet, and I have therefore put it in a very accessible position and carry a piece of copper pipe to insert in its place if there was any blockage. Being further up the pipe work also gives it protection from the sea water filter. If sea weed got in it it would malfunction. Needless to say I have not cleaned it yet and had no need to and we are just back from 10 weeks on the boat down to La Rochelle and covered 1100 miles.
IMG_5275a.jpg
 
Most people have suggested a worn pump body and certainly that was my experience with a Yanmar 2GM. A pump in decent condition will pump air as well as water and so would clear an air lock. Nevertheless, the fact that yours will work in a marina but not after sailing suggests you should re-check the pipe run from the sea cock to the pump to make sure there are no unnecessary kinks etc.
 
I fitted a non return valve to stop a generator (3 cyl vetus 15KVa) being sucked dry as main engine & generator were fed from a main gallery. others have suggested a new pump which will probably fix the problem, however the non return valve will as well.

just a point though, I used bronze flap valve, and at first start of the season it usually needs a clout with the hammer to free it off.
 
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