Anti-Siphon Check Valve

Lawnpro979

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Seems I have a check valve making noise....it seems as f it's blowing air....the one on the other side s quite. And it seems it's sucking air.....

Not sure how these work.....can someone explained. And do I need to replace?
Volvo penta 4.3
Thx
 

Silvertip

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Are you sure you are talking about an anti-siphon valve? This is a device located at the outlet of the fuel tank to which the fuel line is attached. It prevents fuel from siphoning into the bilge should there be a fuel line break or leak. The only way you would have two of them is if you had two fuel tanks.
 

Scott Danforth

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The OP may be talking PCV valves, however PCV valves generally are not used on boat motors
 

Lawnpro979

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Anti-Siphon Check Valve for Volvo Penta Risers the ones on the risers......
 

jimmbo

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He means the check valves that are on the exhaust risers that have hoses that go to the flame arrestor
 

Lawnpro979

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Yea. That's the one........not sure if they work like a pvc valve......but one of mine seems like it's blowing a lot of air out, and makes noise....I can put my finger over it and it quites down......
 

GA_Boater

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Where is the end of the hose connected? EGR valve maybe? Not sure EGR is used on marine engines and it would need more connections to work, so this may be a bad guess.

Not sure what it at all.
 

Fishhead-1

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It's there to allow air into the exhaust if a suction is created on the exhaust side from a backfire or wave action. Basic check valve you should only be able to blow through it one way. Take it off try cleaning out and blow test it. If the hose is getting hot from exhaust gases it's leaking. Mine is charcoal engine also but efi and haven't seen them, maybe only carb engines used them don't know how long.
 

jimmbo

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My 2002 5.7 has them but I never figured out what they did. The hoses are clamped to the flame arrestor with the open end of the hoses against the arrestor fins.
 
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JustJason

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Back in 1996 GM started using roller cams in their engines, those same roller cams hit the marine market a year or two later. When roller cam engines first came out there were all sorts of exhaust reversion issues because boat builders used a shallow static water line measurement. Those check valves act as kind of like an idle relief valve. They take some of the back pressure off of the exhaust system, and it theory, was supposed to help with reversion issues. They never really worked. If you go through some of the old installation books you would see that the static water line measurement was something along the lines of 9 to 10 inches. Volvo then changed to something like 14 inches a few years later, and did away with those check valves. If you have them, check them for signs of water. If you are seeing any water in either of them the risers are rotting. Other than that, don't worry about them or just pull them and stick brass plugs in the risers.
 

Scott Danforth

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Roller cams came out in 1988 for the automotive world and a year or two later for boats. 1996 was first year of vortec heads.
 

Lawnpro979

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So they do work like a pvc valve.....I'm assuming if air is being pushed through...this means the valve could s bad or sticking.....looked up the price and there a little on the expensive side.......
It seems they should be closed unless there is an issue, at that point it would open and allow the discharge to go back into the system?

Nice to finely see that someone knows SOMETHING about engine's.....
 

GA_Boater

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So they do work like a pvc valve.....I'm assuming if air is being pushed through...this means the valve could s bad or sticking.....looked up the price and there a little on the expensive side.......
It seems they should be closed unless there is an issue, at that point it would open and allow the discharge to go back into the system?

Nice to finely see that someone knows SOMETHING about engine's.....

We know about engines, Lawn. We don't know about every engine. Cut us a break, please.

BTW - Did your manual say anything about the valve?
 

Lawnpro979

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Really wasn't asking about every engine....that's why it was posted under volvo penta........
One break, comming up!
 

JustJason

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Roller cams came out in 1988 for the automotive world and a year or two later for boats. 1996 was first year of vortec heads.

​Possibly. All I know is the truck engines came out with roller cams in 96, and those are the line of engines that end up going to Volvo/Merc.
 
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