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Old 18-02-2019, 04:55   #1
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Best vented loop? Maintenance-free?

I have a Groco bronze vented loop (anti-siphon valve) on my raw water engine cooling circuit. While I admit it's a solid, well-made piece of kit, the replacement rubber valve doesn't seem to last more than a year or so before it starts leaking and has to be replaced. At US$ 45 a pop, I'm not so happy about it- and I can't find them in Brazil, so I have to order them from the US and pay shipping and 100% import duty.

Does anyone know of another brand/model that has a simpler valve design (perhaps just a silicone flapper) that just requires periodic cleaning rather than replacement? I see a number of plastic vented loops that go for less than the price of the Groco replacement rubber valve. Any good products that don't require constant replacement of the expensive rubber bits in the vented loop?

Thanks in advance!
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Old 18-02-2019, 05:10   #2
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Re: Best vented loop? Maintenance-free?

Forespar offer a cheaper “Marelon” Vented Loop ☞ https://www.forespar.com/products/bo...hru-hull.shtml
Duckbill ☞ https://www.forespar.com/product514.html
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Old 18-02-2019, 05:18   #3
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Re: Best vented loop? Maintenance-free?

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Forespar offer a cheaper “Marelon” Vented Loop ☞ https://www.forespar.com/products/bo...hru-hull.shtml
Duckbill ☞ https://www.forespar.com/product514.html
Thanks Gordon. That's one of the vented loops I've been looking at. Any idea about the maintenance? Does the rubber part in the valve have to be replaced periodically or does it just need a cleaning every once in a while?
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Old 18-02-2019, 06:04   #4
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Re: Best vented loop? Maintenance-free?

I've used the Scot SS vented loop with no issues. Instead of a flapper valve, the Scot uses a nylon vent with a spring loaded ball valve. Once a year, I'd remove the nylon assembly and soak it in vinegar as a PM. Never a leak or failure.
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Old 18-02-2019, 06:43   #5
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Re: Best vented loop? Maintenance-free?

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I've used the Scot SS vented loop with no issues. Instead of a flapper valve, the Scot uses a nylon vent with a spring loaded ball valve. Once a year, I'd remove the nylon assembly and soak it in vinegar as a PM. Never a leak or failure.
and the Scot nylon vents can be ordered without the loop, you should be able to fit one to the GROCO loop. This is a link to a 3/8 NPT version, they also come with a 1/8 NPT

SCOT DIVISON OF ARDOX - -VB38 Scot Vacuum Breaker 3/8" Female Pipe Thread | MMIMarine.com
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Old 18-02-2019, 08:48   #6
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Re: Best vented loop? Maintenance-free?

I also have the Groco vented loop on my engine exhaust. Once a year I take the rubber valve out, clean it with some soapy water, spray it with a rubber protectant and reinstall it. Doesn't leak and haven't had to replace it since I started doing this each year. I keep my boat in murky water, so if yours is in very salty water you may need to do it more often, but it is easy to do.

Before I installed a composting toilet, I had the Forespar vented loop on my toilet and needed to clean the rubber valve in the vented loop regularly and replace it once every few years so it wouldn't leak. The Forespar rubber valve is a lot cheaper than the Groco one.
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Old 18-02-2019, 09:07   #7
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Re: Best vented loop? Maintenance-free?

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I also have the Groco vented loop on my engine exhaust. Once a year I take the rubber valve out, clean it with some soapy water, spray it with a rubber protectant and reinstall it. Doesn't leak and haven't had to replace it since I started doing this each year. I keep my boat in murky water, so if yours is in very salty water you may need to do it more often, but it is easy to do.

Before I installed a composting toilet, I had the Forespar vented loop on my toilet and needed to clean the rubber valve in the vented loop regularly and replace it once every few years so it wouldn't leak. The Forespar rubber valve is a lot cheaper than the Groco one.
Good advice GoAway. I just installed my (last!) spare Groco rubber valve. It would be easy to remove it every 6 months for a good cleaning. I might stick with the Groco if this works. I did save the old one and I am soaking it now in dish soap and vinegar. Perhaps it will come back to life... (I'll keep it as a spare). I just don't know why a little bit of rubber and stainless steel costs US$45. It seems Groco could price this lower to keep customers happy and loyal to the brand.

Also, thanks for the Scot suggestion above. I checked their site and it looks like a good product. It does state, however, that the valve won't open unless the vented loop is installed at least 2 feet above the waterline. I'm not sure mine is, but I'll check.

The Forespar also looks good and the replacement parts are much cheaper.
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Old 18-02-2019, 09:39   #8
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Re: Best vented loop? Maintenance-free?

The best solution is to eliminate need for maintenance entirely by preventing sea water from contacting the valve. Reposition the vent valve above a hose teed into the wet exhaust line vent loop. See my post in CF last Feb in the "Cooling Water in the Bilge" thread. We sailed 3000 miles last summer and never a drop more water. The valve remained pristine with no salt crystals
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Old 18-02-2019, 09:43   #9
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Re: Best vented loop? Maintenance-free?

An air cushion in the hose is trapped by the pressureized closed valve and replentished when the valve opens to break suction.
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Old 18-02-2019, 10:02   #10
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Re: Best vented loop? Maintenance-free?

Yes, make your own anti-syphon system from small diameter PVC or copper pipe. All that is needed are two threaded elbows, a threaded tee, two 1/8" hose barbs and a length of 1/8" rubber hose long enough to reach the discharge point of the wet exhaust system.

Fashion an upside-down U from the two threaded elbows pointing down and with the threaded tee in the middle of the U pointing up. Install one of the 1/8" hose barbs on the top of the upside-down U. Run a line from the discharge of the heat exchanger to one side of the of upside-down U and another line from the other side to the water injection point of the wet exhaust.

Mount this assembly well above the waterline. Run the 1/8" rubber hose well above the waterline to the discharge point of the wet exhaust. Install the other 1/8" hose barb into the muffler or directly into the through-hull for the exhaust discharge keeping the hose well above the waterline until it can be connected to the muffler or the exhaust through-hull.

Mine goes into the top of the muffler. Periodically, with the engine running, I disconnect the 1/8" hose to check the water flow and to insure that the flow stops indicating that the syphon is broken when the engine is shut off. Mine has lasted 25 years.

It's my experience that commercially made anti-syphons and one-way check valves made for raw water system, heads, holding tanks, etc. on boats aren't worth diddly.
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Old 18-02-2019, 10:35   #11
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Re: Best vented loop? Maintenance-free?

Replace the valve with a small diameter hose barb, attach a hose and run the hose up as high in the hull as you can and then run overboard to thruhull in some inconspicuous place. Did that with the vented loop on my Volvo which kept sticking shut and filling the engine with sea water. One time fix and never a problem there after.
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Old 18-02-2019, 11:06   #12
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Re: Best vented loop? Maintenance-free?

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Originally Posted by roverhi View Post
Replace the valve with a small diameter hose barb, attach a hose and run the hose up as high in the hull as you can and then run overboard to thruhull in some inconspicuous place. Did that with the vented loop on my Volvo which kept sticking shut and filling the engine with sea water. One time fix and never a problem there after.
This!


Vetus sells both kinds....valved and overboard.



I chose overboard as now I have a telltale for waterflow.
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Old 18-02-2019, 11:10   #13
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Re: Best vented loop? Maintenance-free?

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Originally Posted by roverhi View Post
Replace the valve with a small diameter hose barb, attach a hose and run the hose up as high in the hull as you can and then run overboard to thruhull in some inconspicuous place. Did that with the vented loop on my Volvo which kept sticking shut and filling the engine with sea water. One time fix and never a problem there after.

Yes, or you can do what I did and double the exhaust, halving the back pressure and leaving the vented loop as pretty much decorative. But my boat is rather unusual in have side exhausts rather than one stern exhaust. But it also removes the need for a vented loop. Having had issues with failed anti-siphon breaks in the past, had I not done this, I would have gone the "1/4 hose to a skin fitting higher up" route: https://alchemy2009.blogspot.com/201...ng-part-2.html
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Old 18-02-2019, 11:33   #14
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Re: Best vented loop? Maintenance-free?

The vented loop is not really there to reduce exhaust system pressure but rather to break a siphon from the raw water side of the system, where a steady drip through a mixing elbow that is below the water line will fill up the waterlock(s) and eventually reach the exhaust manifold. As with other flooding problems, this happens when the engine is not running (on shutdown for exhaust system related flooding).
Whichever type of vented loop/siphon breaker/ air vent you use, it should be installed between the heat exchanger and the mixing elbow and mounted as high as possible (at least 12 inches above the waterline and on the center line of the boat to allow for heeling under sail with the engine off.
For my own use I prefer the versions that have no valve and simply let air in through a hose connected to a skin fitting high on the combing, adjacent to the helm station so I can see it spitting and know that raw water is flowing. Of course, sometimes that just doesn't fit or meet esthetic requirements and a valved vent is the choice. The modern versions, with miniature joker/duckbill valves are better than the units with springs, imho.


I hope this is helpful
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Old 18-02-2019, 11:41   #15
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Re: Best vented loop? Maintenance-free?

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Originally Posted by JOHNMARDALL View Post
The vented loop is not really there to reduce exhaust system pressure but rather to break a siphon from the raw water side of the system, where a steady drip through a mixing elbow that is below the water line will fill up the waterlock(s) and eventually reach the exhaust manifold. As with other flooding problems, this happens when the engine is not running (on shutdown for exhaust system related flooding).
Whichever type of vented loop/siphon breaker/ air vent you use, it should be installed between the heat exchanger and the mixing elbow and mounted as high as possible (at least 12 inches above the waterline and on the center line of the boat to allow for heeling under sail with the engine off.
For my own use I prefer the versions that have no valve and simply let air in through a hose connected to a skin fitting high on the combing, adjacent to the helm station so I can see it spitting and know that raw water is flowing. Of course, sometimes that just doesn't fit or meet esthetic requirements and a valved vent is the choice. The modern versions, with miniature joker/duckbill valves are better than the units with springs, imho.


I hope this is helpful
John Mardall
Vetus Maxwell Boat Equipment
Thanks for chiming John. I have a Vetus water mufler and it has been performing perfectly going on 18 years!

Could you give an example of (or link to) one of these vented loops with a joker/duckbill valve?
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