Our generator (Northern Lights 12KW) has a vented loop on the raw water cooling supply line. This fall I noted some salt residue in the general area of the vented loop. Then, while servicing the generator, I noted water coming from the top of the vented loop while the generator was running. I removed the fitting at the top of the vented loop - looks like a check valve of sorts - cleaned things up and reassembled. That solved the bulk of the sea water escaping. However, since then I've kept a small cloth over the top of the vented loop and noted when the generator is started we get a bit of moisture on the rag which then dries fairly quickly with the resulting heat from operating the generator. Now that we are back in the US for the holidays I thought I'd take a new vented loop back to our boat to replace the existing - 22 year old - device. So I look on Defender and note the following in the product description of a Forespar vented loop. "All vented loops are designed to have fluids "pushed" through them. If you try to "pull" through a vented loop, you will pull air into the line and not move the heavier fluid. Be sure the pump is on the correct side of the vented loop. ." That makes sense to me from a mechanical/fluid flow perspective. However, in the case of our installation the pump is on the pull side of the vented loop. The NL sound shield actually has two holes in the forward port corner of the top for the raw water supply hose to exit the housing, enter the vented loop, return into the housing, and connect to the input side of the raw water pump located under the corner housing piece. In our case the water flows from the thru hull fitting to the strainer. From the strainer the hose enters the NL housing then up to the vented loop and on as previously described. So I'm confused and would appreciate some guidance. * Do we even need a vented loop on this installation? The presence of the NL housing being set up for a vented loop installation seems to indicate it is expected. * If a vented loop is needed then why is the pump on the pull side of the vented loop and has worked all these many years - or at least the 10 years we've owned our boat? We have 3150 hours on the NL. * If a vented loop is required or preferred on the generator why wouldn't we have a similar configuration on the main engine? We've a single CAT 3208NA that, like the generator, accomplishes the engine cooling via a raw water to heat exchanger system with the raw water then flowing to a water lift muffler and exiting the boat via the engine exhaust flow. There is no vented loop or any other type of anti-siphon arrangement in the CAT's cooling system. The supply line just from the thru hull to the strainer (whose inlet is positioned only inches above the thru hull) and then rises about a foot to the raw water pump inlet where it is pushed into the heat exchanger. Thanks in advance for helping me better understand the use of vented loops. Also, hope you all had a wonderful Christmas and wish you all a great New Year. Don Gillings Figment, KK48NA Presently in Jamaica

Morning Don A few things in your post stand out in my mind. If your anti-syphon loop was plumbed 'backward', water would squirt out of the valve when the engine was running and I'd suspect that you would have noticed it long before now. This is my premise, so I'm assuming that the loop is plumbed correctly. To double check, pull the hose off the side of the pump that you think is the discharge side, start the engine and see if water comes pumping out. If not, that would most likely be the intake side. Once the discharge side of the pump is known with certainty, then the rest of the flow can be followed and the correct location of the anti-syphon loop determined. Another consideration is whether the valve in the anti-syphon loop was installed up-side down, something that in some loops is possible. If the valve is still pliable, remove the valve, blow on each side, and see which direction causes the valve to close, this is the side that should be installed in the loop 'down'. If installed correctly, a leaky valve indicates a fouled valve or an old valve. Anti-syphon valves should periodically be removed and flushed with fresh water, then once clean, reinstalled. Flushing these valves is usually considered a yearly maintenance chore, although I tend to do it only after enough years go by that I start to feel guilty about ignoring this chore. Old valves should be replaced with a new valve. Keep us posted. *Rudy & Jill Sechez* *BRINEY BUG-a 34' Sail-Assisted Trawler * *Anchoring Consultants @ trawlertrainingabc.com <http://trawlertrainingabc.com>* *850-832-7748* Cocoa FL > >