Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 02-03-2024, 10:44   #1
Registered User

Join Date: Apr 2012
Location: Currently in the Caribbean
Boat: Cheoy Lee 47 CC
Posts: 1,028
Syphon Break

I'm redoing the engine compartment while I have the engine out and have good access. As part of this I'm replacing the hoses and syphon break to the raw water to the engine and generator.
I see both stainless and plastic syphon breaks available but they usually say for plumbing applications, I haven't seen any that say their specifically for raw water engine applications.
Any information or thoughts on the subject would be appreciated.
lifeofreilly57 is offline   Reply With Quote
Old 02-03-2024, 13:02   #2
Registered User
 
deblen's Avatar

Join Date: Oct 2014
Location: Bay of Fundy,Grand Manan,N.B.,Canada N44.40 W66.50
Boat: Mascot 28 pilothouse motorsailer 28ft
Posts: 3,256
Images: 1
Re: Syphon Break

I replaced the corroded alum. Volvo Penta siphon break in my boat with a brass home type-designed for domestic hotwater heaters,etc- some 8 yrs ago.
Works fine for me.
Cheers/Len
Similar unit https://www.amazon.ca/Cash-Acme-1738...00MNLNF6&psc=1


Pee tube-another option https://www.moyermarineforum.com/for...ead.php?t=7263
__________________
My personal experience & humble opinions-feel free to ignore both
.
deblen is offline   Reply With Quote
Old 02-03-2024, 13:13   #3
Registered User
 
Uncle Bob's Avatar

Join Date: May 2010
Location: Sydney Australia
Boat: Fisher pilothouse sloop 32'
Posts: 3,420
Re: Syphon Break

Or you could replace the commercial break with a simple "u" bend and fit a small bleed line from the top to either the cockpit drain or directly overboard, no valves to fail, simple and provides a visual confirmation that the pump is operating correctly, just like the telltale on an outboard.
__________________
Rob aka Uncle Bob Sydney Australia.

Life is 10% the cards you are dealt, 90% how you play em
Uncle Bob is offline   Reply With Quote
Old 03-03-2024, 06:38   #4
Registered User

Join Date: Apr 2012
Location: Currently in the Caribbean
Boat: Cheoy Lee 47 CC
Posts: 1,028
Re: Syphon Break

Quote:
Originally Posted by Uncle Bob View Post
Or you could replace the commercial break with a simple "u" bend and fit a small bleed line from the top to either the cockpit drain or directly overboard, no valves to fail, simple and provides a visual confirmation that the pump is operating correctly, just like the telltale on an outboard.
The only problem there is that this is on the suction side of the raw water feed for the engine and generator, so that wouldn't work in this application.
MOst of the syphon brakes I've looked at say they're for toilets and other non-engine related applications. I'm starting to think they've all gone that way for liability reasons. Tough to overheat a head.
lifeofreilly57 is offline   Reply With Quote
Old 03-03-2024, 07:05   #5
Registered User

Join Date: Jul 2016
Location: Atlantic Highlands, NJ
Boat: Swallowed the anchor
Posts: 979
Re: Syphon Break

I don't see the need for a vacuum break on the raw water feed side of the cooling loop as long as there is a vacuum break above the WL somewhere in the loop.

What Uncle Bob suggested is very effective and nearly foolproof. Working on the positive pressure side of the loop makes fitting a vacuum break much easier.
kenbo is offline   Reply With Quote
Old 03-03-2024, 08:51   #6
Registered User
 
Kelkara's Avatar

Join Date: Oct 2016
Location: Vancouver Island
Boat: Hullmaster 27
Posts: 1,043
Re: Syphon Break

Groco make them in bronze and say they are for engine and exhaust applications ... but they won't work on the suction side either. No standard siphon break will ... they break a siphon by letting air into the pipe under suction.
Kelkara is offline   Reply With Quote
Old 03-03-2024, 09:20   #7
Registered User

Join Date: Feb 2006
Posts: 2,771
Re: Syphon Break

Even if a suction occurs when engine is turned off-- just how can it pass thru the vanes on the engine raw water pump? ----and even if it could it would just flow thru the heat exchanger then thru the exhaust manifold and the water cooled elbow and out the exhaust hose back into the water outside. I just dont get this action????
geoleo is offline   Reply With Quote
Old 03-03-2024, 10:19   #8
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,706
Re: Syphon Break

Quote:
Originally Posted by lifeofreilly57 View Post
I'm redoing the engine compartment while I have the engine out and have good access. As part of this I'm replacing the hoses and syphon break to the raw water to the engine and generator.
I see both stainless and plastic syphon breaks available but they usually say for plumbing applications, I haven't seen any that say their specifically for raw water engine applications.
Any information or thoughts on the subject would be appreciated.

I believe this is a common misunderstanding of the application of vented loops. They are to be installed on the outlet (pressure side) of pumps, not on the inlet (suction side).
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 03-03-2024, 11:08   #9
Registered User

Join Date: Jan 2008
Location: SF Bay Area (Boat Sold)
Boat: Former owner of a Valiant V40
Posts: 1,152
Re: Syphon Break

What Stu and Uncle Bob said, in spades!
jamhass is offline   Reply With Quote
Old 03-03-2024, 12:57   #10
Moderator

Join Date: Feb 2010
Location: Australia
Posts: 3,333
Re: Syphon Break

Quote:
Originally Posted by geoleo View Post
Even if a suction occurs when engine is turned off-- just how can it pass thru the vanes on the engine raw water pump? ----and even if it could it would just flow thru the heat exchanger then thru the exhaust manifold and the water cooled elbow and out the exhaust hose back into the water outside. I just dont get this action????
Geoleo, it’s a bit like Russian roulette, mostly the impeller stops in a position that covers both ports in the pump but every now and then they don’t. Then there’s the worn endplate or missing blade that permits the establishment of a siphon, ( it can be a very small inflow)…. And finally, the engine kickback at shutdown , about 5 out of 10 times when I take off a cover plate a couple of the blades are pointing in different directions or one blade is folded flat on itself, engines don’t instantly stop rotating when you activate the stop, one cylinder will always be ¾ of the way up a compression stroke and she’ll rock back a bit.
One of the fatal flaws with new engine installations is the belief that the raw water impeller is a positive seal, and on a new pump it probably is but if the vent loop is badly installed and not functioning , sooner or later an engine flooding is an unwelcome and bewildering surprise for the owner. It’s so common that engineers even have a name for catastrophic early failure of newly installed or rebuilt diesel engines.
Look at it this way, a siphon break could cost you $15-20,000 dollars if you get it wrong.
skipperpete is offline   Reply With Quote
Old 03-03-2024, 13:17   #11
Moderator

Join Date: Feb 2010
Location: Australia
Posts: 3,333
Re: Syphon Break

One more thing….. putting the vent loop too early in the raw water circuit causes another unique problem, too much water in the circuit before the mixer elbow ( or less so on the suction side of the pump) can overfill the Aqualock at shutdown or create a water velocity fast enough to splash back into the exhaust manifold in the absence of manifold pressure, one exhaust valve is always open so cylinder flooding can occur in the worst case scenario but more commonly, raw water splash is often seen as destructive corrosion at the joint between the mixer elbow and the ( usually ) aluminium heat exchanger/ exhaust manifold. The hose for the vent loop circuit need to be the same size as the raw water pump outlet so only use a siphon break that maintains that diameter.
skipperpete is offline   Reply With Quote
Old 03-03-2024, 13:29   #12
Registered User

Join Date: Sep 2017
Location: Langley, WA
Boat: Nordic 44
Posts: 2,506
Re: Syphon Break

You can use plastic or a corrosion resistant metal. I would not use brass. Brass will fail eventually. This is salt water after all. The water is cold sea water, not hot so plastic is fine. Mine is Marelon and original to my now 38 yer old boat.

The vacuum breaker is the usual problem. They can get clogged with salt. A weep tube in place of the vacuum breaker, IOW a small hose that goes well above the heeled water line and drains to a cockpit drain or overboard solves this.

And yes, you can get a siphon if you are missing a vane on your raw water impeller and may not even know it. The pump can function well enough with a missing vane that you would not notice.
stormalong is offline   Reply With Quote
Old 04-03-2024, 03:25   #13
Registered User

Join Date: Jun 2018
Location: Melbourne, Australia
Posts: 489
Re: Syphon Break

Nanni makes one...
https://images.app.goo.gl/j3NJcA2Cebs5kikA9
NevilleCat is offline   Reply With Quote
Old 04-03-2024, 06:18   #14
Registered User

Join Date: Dec 2013
Location: Italy
Boat: Jeanneau 57
Posts: 120
Re: Syphon Break

Vetus also makes them:
https://webshop.vetus.com/en/product...tems/air-vents
Loredo is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problems with Jabsco Anti-Syphon Valve amaryllis Plumbing Systems and Fixtures 26 17-09-2012 17:51
For Sale: Beneteau Anti-Syphon Valve yachtfinder Classifieds Archive 0 18-07-2011 12:53
Onan (?) Anti-Syphon Valve Tudorsailor Engines and Propulsion Systems 6 11-07-2011 15:53
anti-syphon loop repair gettinthere Plumbing Systems and Fixtures 1 09-07-2008 12:04

Advertise Here


All times are GMT -7. The time now is 05:57.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.