Decided to give my fuel system a look while the tank was exposed and was startled at how restrictive and small the anti-siphon valve was. My pick-up is 3/8" ID and I want to make sure I maintain this full opening through out the system. There seems to be very few choices on bigger anti-siphon valves. I know a lot of you are going to say to punt the anti-siphon valve, but in my case I think it's best to have something as the tank sits above the bilge (cat hull). Imco has a bigger one, but its a 90 degree unit that was going to be hard to adapt. I bought an 8 AN Russell check valve that's rated 3 psi to open which seems to be in anti-siphon valve territory. I am going to use this unless I'm missing something obvious...anyone say don't do it?
https://www.summitracing.com/parts/rus-650613

Not a pro... But looks like it should work.

It honestly looks like a great replacement compared to the restrictive stock valves. If you ever have any issues it looks easily to bypass with a couple fittings.

I'd look into that more as, when speaking in pressure differential, 3psi = 6.11 in HG (inches of vacuum)

That valve is designed to be used after a pump to hold fuel between pump and carb or fuel inectors.

Not so sure it would be good as an antisiphon vale....6" vacuum of draw on it from fuel pump is a lot to open it.

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Just found this from a Mercruiser bulletin

Wow! I would have thought the anti-siphon valve would have been stiffer. I guess I won't use the Russell c/v at the tank and no real need for it after the fuel pump if the anti siphon valve is employed.

Do your homework, very possible I screwed up the math. We have two forces going on - one on one side of the valve and another on the other side.

OK, I just found a straght 1/2" NPT x 1/2" hose barb anti-siphon valve. It's made by EVM, part#A/S L-180-B-1/2. The only other one this big I found was made by Imco, but it was a crazy 90 degree thing. I'm going to put a 1/2" npt female X 1/2" barb and just use inline on top of the tank. I realize this thread could be flagged as boring.

I always just knocked the ball and spring out with a punch.

Merc does not want any more than 2 in / hg pulling a vac test for fuel flow on any engine period. With that said regardless what the spec sheets show for any valve you install inline (fuel side ) you will have to check by vacuum testing to make sure its not over Merc specs.

Many boats use this as well (link below) instead of the anti siphon valve / assembly / (ball - spring) - Sea Ray has used this for many years on alot of their apps.

http://www.ebay.com/itm/PARKER-HANNI...-/252387448995