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Old 26-06-2020, 19:15   #1
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Loop vent on perkins 4108

My Perkins 4108 with 200 Hrs on the new rebuild needed a new connection off the raw water side of the heat exchanger. Installed it and immediately filled my sump with sea water. It was original set up I didn't do anything different other than put a anti siphon with a fuel type vent on the top of my sink as It was dangerously close to the water line where it was. Now the raw water side of the anti siphon looks like a waterfall that you get on a hot tub. (Im not liking the ambiance although its great for hand washing during covid). I did three flushes of my motor after the incident there is no more water in the engine or sump. I just feel the vent should not be constantly blowing water and more as the rpms increase. Any suggestions
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Old 26-06-2020, 20:26   #2
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Re: Loop vent on perkins 4108

Thats a horrible thing to have happen but especially so on a rebuilt engine.
Maybe excessive exhaust back pressure, anything that prevents/restricts a free flow of raw water after the vent loop will cause higher pressure in the vent line at the sink. The vent line to the sink should be of a small diameter. How high is the loop at the vent take off point?
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Old 26-06-2020, 20:54   #3
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Re: Loop vent on perkins 4108

Thanks for the quick response Pete!
36” off the take off and another 8” to the sink top . However I did change the diameter of the hose to accommodate the 5/8 vent on the sink top. It was originally 1/4 “ and into the trap of the sink . But almost at Waterline . Being a contractor I thought a bigger vent the more it would breathe ....
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Old 26-06-2020, 21:21   #4
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Re: Loop vent on perkins 4108

36 is certainly more than adequate for a loop height and you definitely have a positive indication that the vent line works but Im puzzled about the water in the sump because if the exhaust hose was blocked with a functioning siphon break, the only raw water in the system at shutdown is the 36 upside of the loop. The downside of the loop would still drain slowly into the mixer and aqualock even with a really restricted mixer elbow
Is the water flow out the exhaust overboard substantial?
its possible that the raw water pump let water into the timing case but there would also be water coming out of the case relief holes
Hows the coolant level?
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Old 26-06-2020, 21:30   #5
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Re: Loop vent on perkins 4108

Quote:
Originally Posted by KaiMarin View Post
Thanks for the quick response Pete!
36 off the take off and another 8 to the sink top . However I did change the diameter of the hose to accommodate the 5/8 vent on the sink top. It was originally 1/4 and into the trap of the sink . But almost at Waterline . Being a contractor I thought a bigger vent the more it would breathe ....
The only time that it will "breathe" is when the engine shuts down and it lets air into the system to prevent a syphon happening, all the time that the engine is running it will be spitting water so the smaller the tube the better. IMHO the tube should be plumbed directly overboard or into a cockpit drain.
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Old 27-06-2020, 13:05   #6
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Re: Loop vent on perkins 4108

replace the valve on the anti-syphon 'U' with a 1/2" hose bib and run the attached hose over board with as high a loop as you can get. The hose through hull may stream water when the engine is running but won't allow enough water to escape that it will affect cooling, When the engine is off it will allow air in the system to prevent syphoning. Beauty of this is there is no valve to stick close and fill the engine with water.
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Old 27-06-2020, 13:23   #7
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Re: Loop vent on perkins 4108

Now the raw water side of the anti siphon looks like a waterfall that you get on a hot tub.

It looks like there is something fishy with your new anti-siphon valve. It should let air IN, not water OUT. Disassemble and check for rubber valve and spring!
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