Anit-syphon vent in exhaust line
- Thread starter Snotter
- Start date
- Status
Hi Snotter,
Here's my diagram from 1981 Catalina 30. My exhaust hose runs along the top of the port locker and down at the transom, no check valve that I can see.
All U Get
Working on picture, drat.
Well I got the picture??????
Here's my diagram from 1981 Catalina 30. My exhaust hose runs along the top of the port locker and down at the transom, no check valve that I can see.
All U Get
Working on picture, drat.
Well I got the picture??????
Attachments
Last edited:
The vented loop is in the water exhaust line between the HX output and the exhaust gas line from the manifold to the muffler. It (the VL) has nothing to do with the large muffler exhaust line that exits at the transom.
On my Catalina 310, the 2" exhaust hose doesn't have a vented loop itself, but, rather, the raw water hose from the engine has a vented loop in it, before it meets with the exhaust elbow. The raw water hose is about 5/8ths ID, so maybe those are the commercially available fittings you have seen?
The vented loop is in the raw water line between the engine and the exhaust water injection elbow. The loop has to be installed higher than any part of the 2" outlet hose.. I think it is a 5/8" or 1/2" hose on my 3 GMF..
Google "vented Loops" and you'll find a size for your hose.. Good luck.
Google "vented Loops" and you'll find a size for your hose.. Good luck.
The vented loop is for the exhaust from my genset. My perkins 4-154 has two vented loops: one between the block and the mixing elbow, and one between the waterlift and the exhaust line to the transom exit. The vented loop in the exhaust line does not look store-bought. Maine Sail one time told me that both are needed and that without one in the exhaust line water from a following sea could be siphoned into the exhaust ports of the engine.
Think about what you are venting guys. the raw water line to the mixing elbow is connected to the raw water (underwater) intake so it can syphon into the boat if you don't have a syphon break. The exhaust is connected to the engine and the air. yes it has water in it (taken care of by the cooling water syphon break) but it is not connected to an underwater anything. So if water does enter at the transom it hits the hump and runs right back out.
Course if the boat is sinking and gets that low you have an additional problem once the exhaust fills up, the engine fills up and water starts coming out the, hey it can't come out at all........ wow imagine that. You don't need a syphon break in an exhaust tube. You do need the hump though.
Course if the boat is sinking and gets that low you have an additional problem once the exhaust fills up, the engine fills up and water starts coming out the, hey it can't come out at all........ wow imagine that. You don't need a syphon break in an exhaust tube. You do need the hump though.
They are not always "needed" in the exhaust line but certainly can be beneficial if your exhaust elbow siphon break is not high enough or your exhaust high loop is not sufficiently high. Your generator should have one before the injection point. As you get bigger in exhaust diameter this often requires a "custom" design using a Scot Pump siphon break and some bronze fittings to make a U... I know of situations where in storms engines have back siphoned despite a siphon break on the exhaust injection elbow but it is rare and very dependent upon internal engine placement, height of the engine siphon break and location of the exhaust outlet.
The installation manual (Onan MDJE) doesn't show a vent, but it also shows an elevation of the exhaust line above the waterline.
I'll see if I can find a Scot Pump siphon break. If not, I will forego the loop since it is very unlikely that I will be running the generator while under way and while under power.
On a side note, I feel good about having the vent in my ehaust line from the auxhilary because the boat squats (not sure if it is a true squat or a stern wave from making way), bringing the exhaust very close to the water. Granted, the boat is used in fresh water, making the chances of a back-siphon occuring slim; hopefuly, that won't be the case for much longer.
I'll see if I can find a Scot Pump siphon break. If not, I will forego the loop since it is very unlikely that I will be running the generator while under way and while under power.
On a side note, I feel good about having the vent in my ehaust line from the auxhilary because the boat squats (not sure if it is a true squat or a stern wave from making way), bringing the exhaust very close to the water. Granted, the boat is used in fresh water, making the chances of a back-siphon occuring slim; hopefuly, that won't be the case for much longer.
BTW - Vetus does sell goosenecks that include vents for the exhaust line - Even in 2". They may work for you, but its likely overkill - http://viewer.zmags.com/publication/066ba269#/066ba269/49
the boat squats (not sure if it is a true squat or a stern wave from making way), bringing the exhaust very close to the water. Granted, the boat is used in fresh water, making the chances of a back-siphon occuring slim; Huh? What does the kind of water you saiol in have to do with the laws of physics and siphoning?
Little or no chance of a following wave parking itself off my stern while sailing on Joe Wheeler lake.
- Status