Engineer Matters
Wednesday March 29, 2017

YachtAndCrew.com

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alfalaval_s_separatorBy a large margin the best but most misunderstood item of machinery in an engine-room is the Alfa-Laval. This company was making cream separators back when Adam was a cowboy;  I remember my Grandfather had one,

and it is still in the family. I say this is the most misunderstood item for a very good reason: the separator can be run
as a purifier or a clarifier.

Clarifier: You don’t want this! A clarifier will remove sludge and some water, but all this is deposited on the periphery of the bowl.

Purifier: This is the only way to go. This will remove sludge and water.
The sludge will be deposited on the periphery of the bowl and water is passed to the water outlet.To change is very easy, but you are unlikely
to have the clarifier disc etc. anyway, so forget about it – stick to the purifier.
This marvellous piece of machinery works by centrifugal force. (Read the manual).
The bowl inside rotates at high speeds (around 9,000 rpm) and it’s the centrifugal force that moves the heavy bits to the bowl
periphery and the lighter fuel is passed out as fuel discharge to daily service the tank. Inside the bowl is a water seal and the volume or thickness
of water is determined by the gravity disc size.

How To Run A Purifier
This needs to be tuned to the vessel; fuel flow and gravity disc.
You only need a fuel flow equal to or slightly higher than being used at full power.
The slower the flow, the longer it takes for the fuel to pass with a better chance of removing smaller impurities.
The gravity disc is the other bit that is always wrong. The larger the disc size the more impurities will be removed.
To select the correct size is simply trial and error. You can get close by reading the manual, but this still requires fine-tuning.
If the cone-shaped discs inside the bowl have heavy deposits, then increase the size by 10 mm. Run the purifier and check the operation.
If all is normal, then increase the disc size by 2–3 mm and keep checking the operation. When you have gone too far, fuel will flow out of the
water outlet. Reduce the disc size by 1–2 mm.

Remember to have the flow reduced to minimum requirements first.
After 20 years, I still haven’t worked on a boat where the purifiers have been set up correctly. This includes one vessel with four purifiers; two
clean LFO fuel for engine and boiler use, one for crank case oil that could be configured to clean rocker oil and the last for marine diesel,
with the FLO and oils being steam heated to reduce viscosity.
Another vessel had a total usage of 650 litres per hour and the flow was set at 2,000 litres.
I only hope all this will help someone understand how this very simple piece of machinery can be made to operate more efficiently. The more
impurities removed, the fewer filters need to be changed. Did I mention to READ the manual ?

Filters
Something I hate to hear is a strainer being called a filter. You have a
suction strainer and a pressure filter – simple. Have a look at any item
of machinery they are all the same. There is NEVER a fine filter on the
suction side of a pump.
Finally, in an article in TYR 62, page 131, called Exhaust Gas Cleaning,
two words in the last line said it all: “good maintenance”. These two
words apply to everything, including the Heiny fridge.


Nigel Brown



S5 Box

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