wet exhaust NR valve - where ?

[MM5AHO]

I want to fit a non-return valve in the exhaust hose. I lengthened the hose last winter to accomodate a calorifier (space), but this was perhaps an error. Now its about 1m between engine and Vetus waterlock, and the water in this loop of hose can come back to the engine, and has done once when heel well over. I'm thinking of a NRV in the hose about 200mm from the engine, but can't find one for fitting in hose (60mm) only (without an attached muffler).

Any ideas?

 

[earlybird]

I'm not sure that a NRV close to the engine is a good idea, even if one can be found. Can you fit a high rise exhaust elbow so as to eliminate the loop and ensure all the water drains into the waterlock?

 

[david_bagshaw]

I want to fit a non-return valve in the exhaust hose. I lengthened the hose last winter to accomodate a calorifier (space), but this was perhaps an error. Now its about 1m between engine and Vetus waterlock, and the water in this loop of hose can come back to the engine, and has done once when heel well over. I'm thinking of a NRV in the hose about 200mm from the engine, but can't find one for fitting in hose (60mm) only (without an attached muffler).

Any ideas?

We fitted similar to a generator years ago, to stop sea slop going in the engine. suggest you try BSS, oakbray, or similar highgrade plumbing supplier. we fitted a chemical grade one wasnt cheap though. Bronze, with ss disc and spring. If no luck try FWB stoke, supplied ours 15 years ago

 

[Tranona]

I want to fit a non-return valve in the exhaust hose. I lengthened the hose last winter to accomodate a calorifier (space), but this was perhaps an error. Now its about 1m between engine and Vetus waterlock, and the water in this loop of hose can come back to the engine, and has done once when heel well over. I'm thinking of a NRV in the hose about 200mm from the engine, but can't find one for fitting in hose (60mm) only (without an attached muffler).

Any ideas?

Suspect you have the wrong end of the stick here. The valve does not go into the exhaust pipe. It goes into the water feed from the engine to the exhaust bend to stop water syphoning back into the engine. See the Vetus catalogue page 177.

There is something seriously wrong if water is getting past your waterlock when heeled. For further guidance on wet exhaust systems see the schematics on page 168.

 

[MM5AHO]

I might not have explained this well enough.
There isn't a problem on the sea water feed side. That has a loop with syphon breaker etc and doesn't back syphon.

Water isn't passing backwards through the Vetus lock.

The problem is the water between the engine outlet (where exhaust hgas and discharging seawater from ythe heat exchanger comes out) and the Vetus.
Normally a very short length of hose, all running downhill towards the Vetus would drain into the Vetus trap, eliminating any reservoir of seawater there.

But now a small amount of water (500ml??) is inside the hose between the engine and the Vetus. This is contained in the hose between the two, which lies in a loop, pretty horizontal, which loops to port and back again. When on the level this is OK, but on heeling to port, it will contain more water, only the exhaust pressure forching it into the Vetus.
If the engine is shut down while heeling to port, there's water in there.
If I now (with engine off) heel to stbd, the loop is no longer horizontal, but looped up in the air, with low points at engine and Vetus. Any water on the engine side of the apex of this now arch shaped loop will drain towards the engine, into the exhaust manifold, and if there's an exhaust valve open, into a cylinder.

My options seem to be:
1. Re-route the hose such that there's no horizontal sections across the breadth of the boat, and preferably all along the centre line, and all falling towards the Vetus. Not easy amongst the calorifier pipework.
2. Fit NRV near engine
3. Continue with draining the pipe on engine shutdown, by closing sea cock and give a short rev to exhaust the water.

 

[earlybird]

I think that your OP explained the problem well enough.
I'm still against the idea of an NRV. OK, this will close immediately on engine shut-down due to the lack of exhaust gas pressure, but, in the next few seconds, despite the anti-syphon valve, a small quantity of water will almost certainly continue to dribble into the exhaust and be retained upstream of the valve. The pressure head of this small amount of water wouldn't open the valve, but it will be held very close to the exhaust elbow, just what you don't want when the boat moves around.
A further drawback is that if the engine is slow to start, ie; lengthy cranking, the exhaust pipe upstream of the valve might quickly back-flood into the engine due to its small volume.
The discipline of opening/closing the cooling water sea-cock every time that the engine is operated wouldn't appeal very much.
I think that your best option is to improve the routing of the exhaust pipe to give a continuous fall to the water-trap. To this end, my earlier suggestion of a high-rise elbow might help.

 

[Tranona]

I might not have explained this well enough.
There isn't a problem on the sea water feed side. That has a loop with syphon breaker etc and doesn't back syphon.

Water isn't passing backwards through the Vetus lock.

The problem is the water between the engine outlet (where exhaust hgas and discharging seawater from ythe heat exchanger comes out) and the Vetus.
Normally a very short length of hose, all running downhill towards the Vetus would drain into the Vetus trap, eliminating any reservoir of seawater there.

But now a small amount of water (500ml??) is inside the hose between the engine and the Vetus. This is contained in the hose between the two, which lies in a loop, pretty horizontal, which loops to port and back again. When on the level this is OK, but on heeling to port, it will contain more water, only the exhaust pressure forching it into the Vetus.
If the engine is shut down while heeling to port, there's water in there.
If I now (with engine off) heel to stbd, the loop is no longer horizontal, but looped up in the air, with low points at engine and Vetus. Any water on the engine side of the apex of this now arch shaped loop will drain towards the engine, into the exhaust manifold, and if there's an exhaust valve open, into a cylinder.

My options seem to be:
1. Re-route the hose such that there's no horizontal sections across the breadth of the boat, and preferably all along the centre line, and all falling towards the Vetus. Not easy amongst the calorifier pipework.
2. Fit NRV near engine
3. Continue with draining the pipe on engine shutdown, by closing sea cock and give a short rev to exhaust the water.

As I said, this is a poor installation. There must be a vertical drop from the exhaust outlet (Vetus suggest 30cm) - or guess what, water will run back into the engine!. The whole point of the waterlock is to prevent this, but it will only work if it is installed properly according to the instructions. I am not aware of any NRV to go into an exhaust pipe.

So, look again at the schematics on p168 of the catalogue on www.vetus.co.uk and figure out how to install iit correctly.

 

[vyv_cox]

NRVs are not the most reliable of items at low differential pressures. I have tried bronze and plastic ones (the latter obviously not suitable for your needs) and find that unless there is a good column of water closing the flap or ball they can be very variable. So, assuming that one can be sourced for your job, I think you might be disappointed in the result.

I agree with Tranona, better to modify what you have to the conventional arrangement than try to find a way of making the unconventional work.

 

[MM5AHO]

thanks for the replies.
I'll manage the valve trick until winter, then when out of the water re-route the hose.
I wish I'd realised this possibility when installing.!

 

[david_bagshaw]

I want to fit a non-return valve in the exhaust hose. I lengthened the hose last winter to accomodate a calorifier (space), but this was perhaps an error. Now its about 1m between engine and Vetus waterlock, and the water in this loop of hose can come back to the engine, and has done once when heel well over. I'm thinking of a NRV in the hose about 200mm from the engine, but can't find one for fitting in hose (60mm) only (without an attached muffler).

Any ideas?

but sometimes the ideal is not achievable for lack of space, etc

the nrv is the bronze item on the galv water pipe.

In this installation, the manifold is on the "wrong side," there is no room at the back or lower down for the vetus water lock, so there is the long wet and gently sloping pipe. All totally wrong.

the nrv has a lightly spring disc, & yes I do agree could trap some water, but better than loads slopping about.

Inour case a high riser is required, a project for the winter, now the engine has been replaced. however the engine has been a problem child since 1991, finally failing in 2008.

the nrv enabled these service years to be eeked out of basically a poor design.