Proper installaton of anti-syphon valve

[Robert1224]

Ahoy,
I have seen to approaches to installing an anti-syphon valve on an diesel with a heat exchanger. 1) install in between impeller output and heat exchanger input and 2) install at heat exchanger output to water input at elbow. As either one of these methods seem as though it would break the possibility of water being syphoned in and causing a hydro lock condition, they both probably work. But now the question: Does anyone here see or have experience with one method being preferred over the other?
Thanks,
Bob

 

[Stu Jackson]

install at heat exchanger output to water input at elbow

^^^^^That one. Any diesel manual will explain why.

 

[kloudie1]

Yup.
http://www.westmarine.com/WestAdvisor/Exhaust-System-Basics

 

[Rich Stidger]

^^^^^That one. Any diesel manual will explain why.

Stu- My factory installed loop is located after the raw water pump and before entry into the engine HX. I can't find an explanation as to why this is wrong. Can you tell me?

 

[kloudie1]

Just thinking out loud (not speaking for Stu) , seems that if the top of the loop is at the same height (always higher than heeled water line), it shouldn't make much difference.. usually the elbow inlet is higher than the raw water inlet, so it is (may be) more convenient (and use a lot less hose) to put the loop there.
Loop on exhaust ell may be an artifact from raw water cooling where there was sometimes no easy access to the discharge of the water pump.
EDIT: more thinking.. Loop on outlet of heatex may keep the tubes immersed resulting in less corrosion/fouling to the tube OD..

 

[Stu Jackson]

Stu- My factory installed loop is located after the raw water pump and before entry into the engine HX. I can't find an explanation as to why this is wrong. Can you tell me?

kloudie is right, Rich. It's simply the amount of space, and on most of the engines I've seen, the only place that allows the vented loop to be high enough and above the waterline is after the HX and just before the muffler. If your boat (or others) do have the room, it appears that either place would function properly to avoid siphoning water back into the engine when it's off and some of the valves are open.