We have two identical RSW units installed on a ship (horizontal oil separator), and one of the units is loosing a lot of oil out into the chiller, we thought maybe the coalescent filters were damaged, 2 months ago I inspected and changed them (they were not damaged but changed to see if it would make a difference.)

from the last feedback from the machinist, the problem unit has gotten worse and is now throwing out close to 20 liters in 24 hours.

the problem unit has also chewed through 2 or 3 shaft seals in short time.

I ran both systems and regulated the main oil injection valve so both systems now run with a discharge temperature between 76 and 81 C ,and 45 - 50 C oil temperature, depending on the speed and capacity position on the compressors.

I measured the temperature on the oil-separator and the temperature on the oil reservoir part of the separator was around 60C +/- 2 C measured at various places. The temperature on the coalescer part was 10 C lower on both units. the temperature of the discharge pipe close to the compressor compared to the inlet to the oil separator had a temperature drop of 4-5 C on both units.

This was measured when the compressors were at 100% and full speed (3600 rpm).

During start up and for maybe 5 minutes I noticed there was a lot of liquid ammonia passing through the oil return line from the coalescer part on both units, also in the oil level glass I could see a layer of liquid ammonia approx 5 mm on top of the oil level, this layer slowly evaporated after the liquid in the oil return had stopped, and it took around 15 minutes before it had dissolved completely after which it was replaced with a 10 mm layer of foam on the problem unit and a 5 mm layer on the good system, this layer stayed throughout the 3 hours I ran the systems.


One thing I noticed was that on the good unit there was a reasonable (normal) amount of oil passing through the oil return after the liquid coming during the start up had stopped, while on the problem unit there was not a single visible drop of oil passing through the sight glass, not even enough to make a distortion on the glass even if I opened the valve fully.

I tried running with the coalescer oil return valve closed for 15 minutes on both units, and when I opened the valves again there was a large amount coming through the glass on the good unit and nothing on the problem unit.


I have been thinking it might be wet suction or the NRV on the suction line malfunctioning, but I didnt notice anything unusual on the LT-LP and if the NRV was leaking the compressor would spool back when stopping and that did not happen.


Any thoughts on things I might have missed?