Problems Alfa Laval LOPX 705

[BigBadEngineer]

Hi.

Hope that there is someone out there who can give me some tips+++

We have a Alfa Laval LOPX 705 LO separator onboard. We have had some problems with one of the separators for almost 2 years.
No help from Alfa Laval.
The problem is that the pressure after the separator varys to much (from 1-3 bars) Its not posible to stabelize it.
Have open and change the pump,paringdisc.
The separator have no lekage on the sludge side, so that is not the problem.

I have some suspions that it can be the supply pump from the engine that can be "broken".
But the chief engineer says that is not the case...????

Anybody out there with any tips or triks????

[Big Pete]

I can see 4 possible causes for the pressure variations:-

1) Variation in temperature/viscosity.
It is normal for the back presure to be high when a L.O. or HFO purifier is started because the lines are full of cold oil from when the machine was last used. The back pressure normally falls back to normal as the discharge pipework warms up.
Is the Oil outlet temperature constant? Should be 95 C for a 4 stroke engine, 90C for a 2 stroke with a scavenge space, 98C for HFO.(All purifier makers).

2) Possibility of a variable restriction in the discharge line.
Sticky non-return valve or similar? Possibly a bit of old gasket or other debris wedged across a valve, or other restriction, that sometimes moves? an internal blister on a flexible pipe? Is this purifier fitted with a "throttling valve" to regulate the back pressure for the loss of seal alarm?
It is possible that a valve is loose on the spindle and can move on its own, changing the back pressure.

3) Variable flow from the purifier.
You have already changed the discharge pump so that should be O.K.

4)Variable flow into the purifier.
Variable flow into the purifier problem with the supply pump as you suggest, or possibly a leak in the suction piping drawing in air. Do you have a problem getting suction when you first start the purifier? If so the problem may well be with the pump or an air leak.
The supply pumps are usually positive displacement type and are therefore fitted with a relief valve, is this working correctly?

I hope this will give you a few things to think about, and I am sure other people will offer their contributions too.
Good luck with your problem solving. Please let us all know how you get on.

[Matthias]

Maybe a faulty pressure relief valve protecting supply pump? Or maybe a faulty pressure regulating valve as mentioned by Big Pete. Its obvious, but has the supply strainer been checked?

[Big Pete]

I have been giving this some more thought.
On the basis that these are the easiest and simplest things to fix, I would check the suction strainer first as Matthias suggests, sorry for missing that out.
I would also check that there is a good gasket on the suction strainer that can not draw in air.
I would also check any valves or change over cocks on the suction pipework and repack their glands to prevent air being drawn in.

One last thought, have you checked that your discharge pressure gauge is reading correctly??? Try changing it for one from another purifier or a spare.
Especially if there is vibration where it is mounted and it is not damped with Glycerine.

Most of us old timers will admit we have wasted huge amounts of time searching for non existent faults, because we were misled by faulty instrumentation!!!

Happy hunting.
BP

[Big Pete]

Hi Big Bad Engineer,

Have you fixed your Big Bad Purifier yet?
We would all like to know.

BP

[BigBadEngineer]

Hi

Sorry for the late response, but we havent had time to adress the problem, we have had a brakedown off one off the ME, so we had\have to priortry this now.

But I will get back to you when we have a sollution