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Old 22-11-2018, 07:10   #1
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Exhaust water separator problem.

I recently replaced my Onan 5KW generator with a Nextgen , but kept my water lift muffler and water separator. The Nextgen is in a sound enclosure and the exhaust runs vertically to the bottom of the enclosure and exits through a 90 degree elbow. The exhaust on the Nextgen is 1.5 inches whereas the Onan was 2 inches. The Onan exhaust exited its sound enclosure about 3 inches higher than the nextgen and at about 45 degree angle. The result is that the Onan had about a 4 inch drop to the side entry of the muffler and the nextgen gas only about a 1 inch drop. The actual exhaust exit from the engine and water injection is at about the same height on both. I used adapter to change the exhaust hose from 1.5 to 2 inches just before the inlet to the muffler. The remainder of the exhaust system remained unchanged. It consists of a Centec vernalift muffler and a Centec exhaust water separator.

Now that I have set the stage, the problem is that the water separator no longer seems to be functioning. Instead of the nice clean constant flow of water out of the water outlet I get a trickle followed by a surge that seems under pressure, going back to a trickle followed by another surge....... It basically acts like my exhausts on my main engines when they are at low speed and of course the do not have a water separator. I sent a message to Centec about this about 10 days ago but have not received a response. Does anyone have any advice on what might be going on? The genset seems to be operating normally, but I am somewhat concerned that there might be too much back pressure in the exhaust.
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Old 22-11-2018, 07:22   #2
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Re: Exhaust water separator problem.

My guess is that the Nexgen is a smaller motor and has less exhaust gas, so the water isnít expelled at a steady rate, but builds up and then is expelled. Going from 1.5í to 2Ē is a significant reduction in gas velocity, and velocity is what carries the water along.
Part of my guess is of course the 1.5í exhaust being connected to a 2Ē.
I donít think it will cause any harm, I doubt you have excess back pressure.
My little Nexgen expels its water at a constant spray, no build up and then purge, but itís also the smaller exhaust hose size, nd mine is the single cylinder 3.5, where I assume yours is the twin 5.5.
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Old 22-11-2018, 07:41   #3
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Re: Exhaust water separator problem.

Iím thinking your water separator drain hose is clogged.
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Old 22-11-2018, 07:41   #4
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Re: Exhaust water separator problem.

I actually think that the base engine is just a modern version of the engine the Onan used. Both gensets run at 2800 rpm and produce 5kw which requires about 11hp of diesel output. The marinized exhaust and heat exchanger is supplied by different companies so perhaps that explains the difference in exhaust sizes or maybe Kubota now gets more hp out of a smaller engine.
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Old 22-11-2018, 07:44   #5
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Re: Exhaust water separator problem.

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Iím thinking your water separator drain hose is clogged.
The water and exhaust are coming out of the water hose, but I suppose the exhaust outlet might be clogged.
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Old 22-11-2018, 07:57   #6
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Re: Exhaust water separator problem.

I guess I should point out that the Exhaust was working perfectly the day the Onan was removed and I made no changes past the inlet of the muffler before the nextgen was installed 3 days later. There wasn't much opportunity for something to get broken..., but it is a boat.
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Old 22-11-2018, 07:58   #7
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Re: Exhaust water separator problem.

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The water and exhaust are coming out of the water hose, but I suppose the exhaust outlet might be clogged.


Ahhh, I had misread your problem. What size is the water drain hose? Maybe itís draining too quickly?
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Old 22-11-2018, 10:48   #8
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Re: Exhaust water separator problem.

can someone explain the reasons for the two additional Centec units. i had an Onan 4kw unit [late 80's] with a 3 cyl kubota running at 1800rpm. the mixed exhaust fed a waterlift muffler, via a 6" drop, the output of the waterlift went directly out via a 12' hose with a 24" rise and fall. water exited in spurts as the water lift filled and purged. so it seems the additional Centec units are redundant and add more back pressure to the exhaust stream.
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Old 22-11-2018, 11:42   #9
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Exhaust water separator problem.

The additional Centek unit is a water separator. It of course removes the water eliminating the splash that can produce noise.
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Old 22-11-2018, 11:51   #10
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Re: Exhaust water separator problem.

Please clarify, Captain Bill - is the condition you're describing occurring while the genset engine is idling or under load and at generatiing speed?
A separator is such a simple piece of gear that it's unlikely to be causing a problem, and if your new genset is idling while not producing electrical power, you probably don't have a problem. It's also possible that your new smaller engine is just pumping less raw water than the old engine, so the waterlock is taking longer to fill up and spit out when the gas pressure builds up.


No connection with Centek, of course, but let me know and I'll make some suggestions.


All the best
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Old 22-11-2018, 12:29   #11
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Re: Exhaust water separator problem.

The Nexgen doesnít Idle, it runs at a constant speed of I think 2850 RPM. However of course if you load it up, exhaust gas volume and velocity go up some.
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Old 22-11-2018, 12:37   #12
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Re: Exhaust water separator problem.

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Originally Posted by JOHNMARDALL View Post
Please clarify, Captain Bill - is the condition you're describing occurring while the genset engine is idling or under load and at generatiing speed?
A separator is such a simple piece of gear that it's unlikely to be causing a problem, and if your new genset is idling while not producing electrical power, you probably don't have a problem. It's also possible that your new smaller engine is just pumping less raw water than the old engine, so the waterlock is taking longer to fill up and spit out when the gas pressure builds up.


No connection with Centek, of course, but let me know and I'll make some suggestions.



All the best
John Mardall
Vetus Maxwell Boat Equipment
It is happening at all loads. The engine runs at a fixed RPM though I guess the exhaust volume might vary a bit with load. As I under stand the water separator it's basically three pipes coming into the bottom the intake being medium height, the water outlet the shortest and the exhaust outlet being the tallest. The water comes in the inlet in spurts from the vernalift muffler, the water being heavier than the exhaust falls to the bottom and overflows like a standpipe, and the exhaust gasses flow out the tallest pipe at the top. The water in mine is coming out in spurts just like there was no separator. I suspect that the water outlet might have some kind of fitting on it to prevent it en-training the exhaust gasses and smoothing the flow. I wish I could get an answer from Centec. I'm wondering if I need to go to a smaller muffler? The 2 inch model may be collecting too much water before it empties and simply overwhelming the separator. interestingly Centec sells a 1.5 inch muffler but does not seem to offer a 1.5 inch water separator.
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Old 22-11-2018, 18:34   #13
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Re: Exhaust water separator problem.

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The water in mine is coming out in spurts just like there was no separator. I suspect that the water outlet might have some kind of fitting on it to prevent it en-training the exhaust gasses and smoothing the flow.

So the exhaust gases come out a different hull fitting, presumably above the spurting water outlet and both are above the waterline ?

If so, you could check for a blockage in the gas outlet by holding your hand close to it. If there is little or no exhaust gas escaping there you could even temporarily block that outlet (for a few seconds) with a rag and see if that changes the water spurts. If it doesn't, you got one more hint. Maybe a kink was unknowingly introduced in the gas line during the refit.
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Old 23-11-2018, 05:42   #14
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Re: Exhaust water separator problem.

Quote:
Originally Posted by Captain Bill View Post
It is happening at all loads. The engine runs at a fixed RPM though I guess the exhaust volume might vary a bit with load. As I under stand the water separator it's basically three pipes coming into the bottom the intake being medium height, the water outlet the shortest and the exhaust outlet being the tallest. The water comes in the inlet in spurts from the vernalift muffler, the water being heavier than the exhaust falls to the bottom and overflows like a standpipe, and the exhaust gasses flow out the tallest pipe at the top. The water in mine is coming out in spurts just like there was no separator. I suspect that the water outlet might have some kind of fitting on it to prevent it en-training the exhaust gasses and smoothing the flow. I wish I could get an answer from Centec. I'm wondering if I need to go to a smaller muffler? The 2 inch model may be collecting too much water before it empties and simply overwhelming the separator. interestingly Centec sells a 1.5 inch muffler but does not seem to offer a 1.5 inch water separator.


Is the water spurting out of the water outlet, and the exhaust is dry out of the exhaust outlet?

If yes, the new generator is moving less water than the old and the water separator is draining too quickly.

Try throttling the water drain in an attempt to keep the separator more full rather than dry enough to allow exhaust gas out of the water drain.
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Old 23-11-2018, 11:58   #15
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Re: Exhaust water separator problem.

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Originally Posted by hzcruiser View Post
So the exhaust gases come out a different hull fitting, presumably above the spurting water outlet and both are above the waterline ?

If so, you could check for a blockage in the gas outlet by holding your hand close to it. If there is little or no exhaust gas escaping there you could even temporarily block that outlet (for a few seconds) with a rag and see if that changes the water spurts. If it doesn't, you got one more hint. Maybe a kink was unknowingly introduced in the gas line during the refit.
The gas outlet is a straight drop of about 16 inches. There is no way for it to kink. The genset is located on the bridgedeck and the gas exits directly through the bridgedeck, while the water hose is routed through the port hull and exits about 6 inches above the waterline.
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