Hi Big Pete,
At first I am sorry for very late reply.
You got the real picture. We recollect the fuel oil same way you described. We do all the changeovers by manual valve and diaphragm pumps.
Our LO purifiers are working excellent. We faced the problem for only HFO purifiers.
No, shortening de sludge interval not solving the problem. Other way our HFO quality is good, sludge product rate is less. So there in no point to shorten the de sludge interval.