fresh water temperature problem

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chrls.antny
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Joined: Sun Feb 05, 2012 2:47 pm

fresh water temperature problem

Postby chrls.antny » Fri May 11, 2012 3:02 pm

hi guys , in a generator in our ship since i joined i have never seen temperature fall behind around 70 degrees , we had been at dock some sometime , they did all cleaning and maintenance work on generator coolers . we started the generator three days before , since then fresh water temperature is around 43 degrees , it never went up more than 47 degrees even with more than half load . no one is concerned about it . is there any way possibly fresh water temperature can be around 40 degrees . i am thinking it is mixing with seawater in cooler . header tank condition is normal only . most of the people here am working with have panama certificates . so as long as the generator is running they wont care about anything . am just 3 months in to my maiden sailing . please share your views guys .

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JollyJack
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Re: fresh water temperature problem

Postby JollyJack » Fri May 11, 2012 6:05 pm

sounds like the cooler 3-way bypass valve. Jacket temperature should be higher than that. The valve may be installed backwards so all the cooling water goes through the cooler all the time, or the innards might be described by the technical term "kerfukticated". You never said where you were, sea temperature may have an effect. To check for salt water contamination in the header tank, take a sample of the water and add a few drops of siver nitrate. If it turns cloudy, you have salts.
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Big Pete
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Re: fresh water temperature problem

Postby Big Pete » Sat May 12, 2012 4:03 am

Hi Chris, welcome to the Forum, and congratulations on realising that there is something abnormal about this engine and wanting to do something to correct it.

1) I would normally expect the engine jacket water outlets to be about 75C but some engines should be run hotter and you have to check the manuals to find out the correct operating temperatures and pressures.

2) Have you double checked what the actual outlet temperature of this engine is? Maybe the thermometer is faulty, if you can hold your hand on the jacket water outlet pipe it is too cold.

3) If the engine really is too cold, the most likely explanation is a problem with the thermostat. On two ships now, I have seen the wax bulb thermostatic elements of the auxiliary engines were removed by a previous Chief Engineer in response to a problem with the temperature being too high. " Everyone knows that removing the thermostat will lower the temperature" as one Chief wrote in his monthly report to the Office. In fact the cooling water coming out of the engine has two choices, go straight back to the pump suction or struggle through a cooler first, so removing the elements is most likely to raise the temperature, not improve cooling. (The thermostats expand and close the cooler bypass passage when they get hot)

4) Depending on the type of thermostat many different things could be wrong, if it is mechanical it may have simply seized up if the cooling was drained out for a long time. If it is electrically or mechanically operated, maybe someone just shut off the air or power while they were working on the engine and never put them back on.

5) If there is an adjustable set point for the desired temperature value, maybe someone has just set it to the wrong value.


6) Some thermostatic valves, particularly those types driven by an electric motor have an emergency mode, in which the electric motor is disengaged and the the valve moved by a manual control wheel. That leaves the motor turning but not moving the valve. I have also seen one of these assembled incorrectly, the valve spindle and motor gear box shaft were different diameters and clamped together by a split bush with different bores at each end. Some one had put the bush back upside down!!! The small bore was tight on the large shaft and the large bore wasn't even touching the small shaft.

I hope this information helps you, Let us know what you find, and we can give you some more advice.
It sounds like you are on the sort of the ship where you have to learn fast in order to survive, Good Luck.

B.P.
It is always better to ask a stupid question than to do a stupid thing.

chrls.antny
Bilge Dweller
Posts: 7
Joined: Sun Feb 05, 2012 2:47 pm

Re: fresh water temperature problem

Postby chrls.antny » Thu May 24, 2012 3:45 pm

JollyJack , BP thanks for your valuable guidance . i have been at sea so couldnt post a reply earlier . i checked the manual . they had given as the 3 way by-pass valve automatically maintains the temperature at 76 degree and temperature upto 85 is reasonable . no hand wheel also provided . they had given the type of 3-way valve as AMOT . i feel like the problem is in the by-pass valve only . got another question too . we have MC type MAN B&W main engine . when doing check opening the scavenge drain , is little smoke is normal ? . if it is completely dry without any oil with only smoke isnt it a problem . what kind of scavenge drain condition would be a satisfying one . thank you guys

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Big Pete
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Currently located: Solihull, England

Re: fresh water temperature problem

Postby Big Pete » Thu May 24, 2012 11:30 pm

Thanks for the feedback.

I would open up the Amot valve and check it, it may have failed, usually they are very reliable and maintenance free, but if cooling water treatment is not maintained correctly they can become choked with scale or corrode away.

With regard to the scavenge drains, if you have smoke, you have piston blow by. Your piston rings aren't sealing properly. YOU SHOULD have some liquid in the scavenge drains, unfortunatly you may have the cylinder lubrication rate far too low, and as a result damage to the piston and liner.

Check the recommended cylinder oil feed rates against your actual consumption. In my experience with Third World crews you can not rely on the figures they put in the log book for a daily consumption. It is better either to check it yourself or go by the end of month Remains on Board figure and the running hours for the engine for the month.
Depending on the cylinder lubrication type you may have to adjust the stroke of the individual pumps or adjust a mechanical linkage to change the drive ratio.

Sometimes people fit new or overhauled cylinder LO pumps, (Standard factory setting is for maximum delivery) and find they have a massive LO consumption. They then change the mechanical linkage to reduce the consumption!!!
Then both the pumps and linkage are set wrong. The maker's manual should have all the details for adjusting your system correctly to give the correct lubrication at ALL LOADS.
It is in order to maintain correct lube at all loads that there are so many ways of adjusting the feed rate. On Sulzer RTA you can adjust the stroke of each individual pump, adjust the link, and rotate the gear while in the drive, in order to obtain the correct feed rate at all loads. The original settings should all be shown in the original workshop trial data if you can find that. IT IS A WONDERFUL SOURCE OF INFORMATION>

Good Luck, BP
It is always better to ask a stupid question than to do a stupid thing.


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