Alfa Laval SU 821 separator damaged discs

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The Dieselduck
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Alfa Laval SU 821 separator damaged discs

Postby The Dieselduck » Fri Aug 07, 2015 11:21 am

Hello everyone,

Dave Steel here. New to the forum, long time visitor to the site.

Since installation of the alfa laval SU 821 separators onboard, we have found damaged discs during disassembly of the bowl. This includes the first disassembly after installation. (came from factory this way) The first time was warrantied. However, we continue to find the first
3-4 discs damaged at the vertices of the indexing notches. They are rolled up on one side only. I must stress that extra care has been taken since we initially discovered this. Yet despite this care and strict adherence to alfa lavals instruction, it keeps occurring. I even went as far as using a dial indicator to ensure compression of the hood was within a couple thou during each turn of the screws.
regardless, the discs were being damaged. since 2008, chiefs, down to 3rds have experienced this issue. doesn't seem to matter who does it or the diligence assumed. we run diesel only through these units and only from reputable sources along BCs coast. The units are in very good shape otherwise. Furthermore, Alfa Laval states in the manual that during disassembly, the compression screws must not exceed 60Nm when compressing the hood. Then during assembly, its 40Nm. And finally under "checking stack pressure" it states 50Nm. We have Ideas regarding the difference in torques but seek other opinion. Has anyone seen this or have any ideas? This is happening on both units so I don't believe this to be an isolated incident.

Regards,

Dave

S and P_Flex separation systems.pdf
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Big Pete
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Re: Alfa Laval SU 821 separator damaged discs

Postby Big Pete » Sun Aug 09, 2015 1:00 am

I haven't sailed with these too new for me!

If one edge of the notch in the plates is turned up, it sounds as if the plates are trying to turn during operation
Which side of the notch that has turned up will tell you which direction the plates are trying to turn and therefore if it is happening when you are accelerating (running) or decelerating.
If it is worst on the top plate and progressively less down the stack it is presumably caused by friction from the Hood and it is the Hood that is turning dragging the plates below it by friction, the Torque reducing with each interface,
Is the Hood properly keyed into the spindle? That sounds like the most probable root cause.
Too many or damaged plates could cause the Hood to be too high on older purifiers with locking screws, but with this design of a snap ring that should not be possible, as the Hood HAS to be pulled down far enough onto the spindle to engage the locating ridge in order to get the snap ring in.

Good luck, and keep us updated on progress.

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


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