Installing marine exhaust check valve - genny

[rgano]

I have now suffered two water instrusion events through the exhaust system on my low-mounted NextGen 3.5 KW generator. It is at the repair shop now, but when I goes back in, I want to install a check valve in the 2-inch exhaust hose downstream of the lift muffler. Does anybody know if there is an orientation preference, i.e. vertical or horizontal? Mounting vertically is probably impossible anyway, but I thought I would check to see if a horizontal mount is predjudicial to good order and discipline in the exhaust stream.

 

[rslifkin]

Are you sure the issue occurred because of water getting pushed up the exhaust and filling the lift muffler? If the system geometry is poor I could see water already in the lift muffler (and the hose feeding to it) sloshing back into the engine under the right conditions.

 

[mvweebles]

Is there a reason you can't do a proper install? See attached from Northern Lights. There are two ways water can enter the engine. One being the exhaust as you mention. The other via the raw water pump which is why it must have a vented loop between the pump and the engine. Make sure you're addressing the right issue. If your vented loop had a simple duck bill valve, these need to be serviced periodically.

My boat too is low in the water. Was tricky to get the exhaust high enough - had to scavenge lower 6 inches of a cabinet.

Peter

 

[rgano]

Yes, I am sure, because the boat was moored in such a way that 3-foot waves washing through the bayou during a winter storm pushed perpendicularly to the hull where the outlet is. I went out and got the water out of the cylinder afterward by removing the single-cylinder's glow plug and cranking the hydro-locked engine to get the water out. Prior to this event, the engine was run weekly while waiting for the lift the boat normally lives in to be rebuilt. It's a VERY low and vulnerable installation about which nothing can be done due to the boat's low profile. After the flooded cylinder event, I plugged the exhaust outlet, removing it for the weekly run, until the lift was back in place 18 months after being blown down.

 

[rgano]

I will solve the issue with a check valve, just need to know that its orientation is not a big issue. Access to a horizontal install is a snap.

 

[DavidM]

Check with Centek, who makes these check valves, but I am pretty sure they are designed for horizontal installation.

You probably have considered these solutions, but the geometry doesn’t work: raising the exhaust spillover height to at least 12” above the waterline, putting in a surge tube, and most unlikely installing an equalization line like the 34T.

I am not a particular fan of check valves- they can stick open and you have no way of knowing it.

David

 

[Mac2]

The quality of the check valve makes a big difference along with orientation. I've seen clear check valves that allow you to see the status of the valve. If you do the horizontal check valve they will specify having the hinge of the valve on top so gravity helps it work/close. They are not as hardy as the bronze check valve. The bronze valve is also heavier, which help it close better as well.

 

[rgano]

Thanks for the inputs. This valve is coming from CenTeK, and I have also sent them a note asking for their advice, and I would guess the instruction with it may include to part about keeping the hinge on the topside, but I will ensure that happens. I wish there was a way to invoke the fine suggestions about using higher rises etc, but it cannot happen here. Luckily my 315 HP Yanmar's exhaust mixer is about a foot higher than the generator's and did not suffer any water intake in the storm. Even if I could remove the generator's exhaust mixer from the skid and raise it about 8-9 inches higher, I would be afraid of un-expelled water in the lengthened hose falling back into this tiny generator's cylinder. The check valve will hopefully never be put to the test because the boat is now back in its lift and unlikely to ever again be moored in the manner which exposed it to this casualty, but i will feel better abut it being there.

 

[SIBERNUT]

FWIW, I just listed a bronze thru hull & piping in lncl a bronze check valve. BUT - it is only 1.5"

 

[Mac2]

I'm guessing you don't have a ball/gate valve at the thru hull. Mine doesn't either. It does have a loop above the waterline, but I always wondered why they wouldn't have installed one at the time of the build as way to stop water ingress if a hose went bad, or for repairs (or situations like you had). My generator exhaust is the only thru hull without a ball valve. Wonder why?

 

[Arc]

The generator itself should be above the water line. That will put the pump at least 12” above water. Then the muffler should be below that. The vacuum break should be after the heat exchanger and above the exhaust discharge outlet

 

[CharlieO.]

Would an exhaust flapper help? I'm considering adding one for my main.

 

[Keysdisease]

David's advice is spot on. The last sentence may not be an issue as the boat is home on a lift now. I'm pretty sure the check valve is clearly marked "top," and I'm also pretty sure horizontal is correct orientation. This is based on observing many of these installations that were all horizontal.

Check with Centek, who makes these check valves, but I am pretty sure they are designed for horizontal installation.

You probably have considered these solutions, but the geometry doesn’t work: raising the exhaust spillover height to at least 12” above the waterline, putting in a surge tube, and most unlikely installing an equalization line like the 34T.

I am not a particular fan of check valves- they can stick open and you have no way of knowing it.

David

 

[mvweebles]

Rgano - I'm back at the boatyard for the day. Noticed this elbow into a mushroom thru-hull that I'm guessing is a generator outlet. Made me think of your situation.

Peter

 

[garbler]

I’ve had a number of hydro-locked engine loss claims attributable to check valve installations. From my experience I’d stay away from them no matter what the manufacturer says they will do. In a diesel exhaust stream they can collect exhaust deposits that form hard and can jam the valve. I’ve seen it in ball types and swing gate types. Even if the valve doesn’t completely fail but hangs up they tend to restrict flow and thereby increase exhaust back flow pressure. I’m not aware of your systems design and whether it’s proper or safe but I’d suggest enlisting somebody who is competent in wet engine exhaust systems help you out. Wave action in way of your genset exhaust port is no excuse for flooding your engine. Something, ie, elevations are wrong.

Rick

 

[BruceK]

I once had a sailboat with a small Volvo engine. One day, after sailing offshore well heeled to port where the exhaust exits,on starting it broke the crankshaft. A new engine was an expensive but economic solution, sadly I lost the decompression lever and hand crank start ability.
It already had a Vetus anti lock swan neck "thing" in the exhaust line, and I managed to create a high loop of the exhaust line,but sometimes there was a start hesitancy indicating it was locking, I would pull the exhaust line off the Vetus "thing" freeing some water and pressure and safely start it.
Unless you can resolve a similar issue, listen to the genset while starting.

 

[rgano]

The generator itself should be above the water line. That will put the pump at least 12” above water. Then the muffler should be below that. The vacuum break should be after the heat exchanger and above the exhaust discharge outlet

Yup, that's pretty much the cooling water setup. The problem was the perpendicularly impinging 3-foot waves pushing water up the exhaust hose filling the muffler and continuing right up and over the arching hose and into the tiny mixer and thence to the engine.

 

[rgano]

Here is my newly installed 2" Centek exhaust check valve, mounted horizontally with the suggested 1/2" dropped to the downstream end and hinge upward. Luckily, for this installation anyway, I had to cut this access hole in the cockpit deck years ago to service the Vacuflush vacuum generator (THANKS, Mainship, for that bit of poor engineering), making easy access to the generator exhaust run between muffler and hull exit. If this exit had been installed on the transom instead of the side of the boat at the waterline, I'd have saved money and just screwed a rubber flap to the hull over the exit. Ho hum.

 

[Keysdisease]

Direction of flow, this side up. Gotta Love it when they try and make it simple

 

[OCEANA]

I put large bronze ball valve on my exhaust. I closed it when away from the boat and opened it to run. An extra step, but good insurance for when I was away.

 

[Steve DAntonio]

I realize you are constrained by space, but does the hose between the genset's mixing elbow and muffler slope continuously downward? Ideally, the drop between the elbow and the water lift is a minimum of a foot.

In the photo it looks as if water can collect on the outlet side of the check valve, if so that could be an issue as water could eventually leak past it, the seal is not a perfect one.

Generally, i hate to rely on a check valve to keep water out of an engine, primarily because there is no way to know if the check valve is intact, I've encountered at least two where the flap was missing entirely (I haven't checked recently but I suspect CenTek, which makes excellent products, requires a visual inspection at regular intervals, not exactly an easy task).

More on engine flooding from this scenario here https://stevedmarineconsulting.com/flooding-vs-siphoning/

And this https://www.proboat.com/2011/03/generators-done-right/

In cases like this I have installed a clamshell over the exhaust on the hull.

 

[Duetto]

rgano,

do you have the new exhaust elbow? our original (circa 2003) basically came straight down from the exhaust port. the newer one rises at least 6" before turning down. we have a 34 pilot but problem is much the same. genset shelf is basically waterline.

 

[rgano]

rgano,

do you have the new exhaust elbow? our original (circa 2003) basically came straight down from the exhaust port. the newer one rises at least 6" before turning down. we have a 34 pilot but problem is much the same. genset shelf is basically waterline.

Yes, new type.

 

[rgano]

I realize you are constrained by space, but does the hose between the genset's mixing elbow and muffler slope continuously downward? Ideally, the drop between the elbow and the water lift is a minimum of a foot......

Thanks for the post, Steve, and yes I am constrained in this installation in every way imaginable. I think most MS 30 Pilot IIs do not come equipped with a genny, and this factory install seems to be more of an afterthought than a well engineered setup. Any photo I can find of the exhaust mixer on this Generator is of the older can-style and NOT the setup mine came with new in 2018. I will have to take a thorough set of photos when it returns from the mechanic's shop, unless we go with an insurance claim and just do a wholesale replacement. The generator is mounted in a tray with integral sound hood, and in order for the exhaust hose to not interfere with the removal of the hood, the exhaust is directed down and out the bottom of the tray, basically at the level of the generator shelf itself. The top of the hood is actually in contact with the deck above and whole unit abuts the aft bulkhead of the engine compartment. The lift muffler is on the same level as the generator shelf (cannot go lower in this boat) on the other side of the bulkhead which requires the exhaust run to climb from shelf level to about the same level as the exhaust gooseneck on the generator itself to then run aft and down to the lift muffler and then up again before descending to the level of the new exhaust check valve and down a couple more inches to the hull exit.

 

[Easternshore]

raise the genny

Hi Rich, I had a similar issue with my MS Pilot34, when I replaced the generator with a new one they said it‘s low position was a common problem with the Pilot. They built a small platform with 2x4s on end & plywood which raised the genny a few inches and alleviated the issue. I hadn’t had a problem after their fix. Not sure if you’d have sufficient headroom to raise it on the 30.
Regards, Ed

 

[MOJO]

I put large bronze ball valve on my exhaust. I closed it when away from the boat and opened it to run. An extra step, but good insurance for when I was away.

This is the "correct" solution and it's what's on MOJO. If the generator isn't running, close the valve and put a flag on the start switch to remind you to open the valve before starting.

 

[rgano]

Hi Rich, I had a similar issue with my MS Pilot34, when I replaced the generator with a new one they said it‘s low position was a common problem with the Pilot. They built a small platform with 2x4s on end & plywood which raised the genny a few inches and alleviated the issue. I hadn’t had a problem after their fix. Not sure if you’d have sufficient headroom to raise it on the 30.
Regards, Ed

That's what I'd do if the height was available. I got under there yesterday looking at the rise of the exhaust hose after it exits the genny and goes over the hump of the half bulkhead and then back down to the lift muffler under the cockpit deck to see if I could lower that rise. Ideally, I would have rerun the hose to pass it through the same hole lower down on that bulkhead where the Yanmar's exhaust passes through; but the genny's hose is too stiff to push back through the gap; and although I could touch the inlet of the muffler, there was no way for me to actually disconnect the hose and pull it back to me for a rerun. I would have to cut a massive access in the cockpit deck and step to properly access the muffler - not gonna happen. In the end, I was able to lower the rise an inch or two rather than the six inches available through the lower bulkhead pass-through.

The idea of placing a bronze valve in the exhaust without some form of emergency pressure relief AND an ignition interlock is, to me, fraught with unimaginable consequences, and I will remain happy with a what looks to be the good solution of a check valve in a location where I can easily examine its operation over the years. And remember, this is a lift-kept boat which got caught moored beam to a storm while forced to be in the water after the lift was destroyed. If it ever gets stuck in the water again, I'll reverse the moor, even with the check valve installed.

 

[SIBERNUT]

I have a 1 1/2 bronze check valve with a WC thru hull etc on Craig's here. PM me if interested.

 

[rgano]

I have a 1 1/2 bronze check valve with a WC thru hull etc on Craig's here. PM me if interested.

Thank you very much for the info, but already I have the in-line one in place.

 

[rgano]

I am back to sort of wrap up this thread because I have had a lot of time while the generator is out of the boat and the insurance claim proceeds to scrutinize the exhaust line of my generator and to compare it to other exact model boat/genny installations. As it turns out, the B team was definitely at work when this exhaust was installed. As a refresher, the single cylinder 3.5 KW genny sits slightly above the water line, and the cooling water line is installed with a vacuum breaker. The generator was ALWAYS run on freshwater after every use, and the boat lives in a lift.

Both main and generator exhaust systems were installed before the deck mold was added to the boat making access to the system difficult to impossible.

The genny is equipped with an exhaust loop running to the top of the sound enclosure which touches the deck above - can go no higher. The 1.5-inch ID exhaust hose then exits the generator skid at the very bottom of the box before climbing nine inches in low angle to get over the bulkhead between the generator and the lift muffler. Other boats like mine have a hole cut into the bulkhead lower down allowing a fairly level run to the muffler - no problems have been experienced there. I realize that there should be a downward run to the muffler, but in this small vessel, such is impossible. I must fault the factory installers for this clownish exhaust run.

The generator tear-down revealed severe pitting of the piston and the valves and valve seats. While some of that corrosion was likely the result of almost a week of saltwater hydrolock after a storm forced seawater into the exhaust system while the boat was moored in the water, I have come to believe that continuing backflow of un-expelled water (seawater and/or freshwater rinse) in the slow rising exhaust hose from the generator contributed to the corrosion due to excessively hot and humid conditions at the engine.

I have finally mustered up the courage to cut an access hole in the bulkhead to the tiny lift muffler and have removed the original run of exhaust hose over the bulkhead. A new hose will run directly to the muffler with a rise of a couple of inches to the muffler input. The muffler output rises up to possibly as high as the exhaust mixer loop on the generator, but the volume of water there is apparently not sufficient to backflow up and over that loop toward the engine. Shutting off rinse water a few heart beats before hitting the stop button on the genny will also promote better conditions at the engine's exhaust.

I will depend upon the new check valve after the muffler to protect against water forced into the system by storms through the hull exhaust port.

Anyway, the insurance settlement has provided enough money to rebuild the engine (only 134 operating hours since I bought it in 2018, mostly just monthly runs to load it up), and then we will try again.