147.Framo Cofferdam purging

Purging of the cofferdam is one of the most important preventive maintenance routines when operating a Framo submerged cargo pump. This is a unique way to check the pumps seals and thus the condition of the pumps, without entering the cargo tanks. Any leakage over the seals will collect in the cofferdam, and through regular purging the leakage rates can be determined and action (if necessary) can then be planned which will ensure safe and trouble-free operation of the cargo pump.

 Cargo leakage 

A small leakage rate of up to about 0.5 l/day (and higher with light cargoes) during pump operation is normal. Acceptable leakage rate depends on the type of cargo and possible consequences in case of leakage. - Risk for clogging of pump cofferdam Cargoes like naphtha, condensate etc. penetrates the shaft seals more easily than lubricating oils, vegetable oils and other viscous cargoes. It is therefore recommended to carefully monitor the leakage rate over a period of time, preferable with different type of cargoes. For critical cargoes, when the leakage rate is about 2 litres/day or higher, the pump must be purged a couple of times daily and service (leak test and repair) carried out at first opportunity. Intensify the purging if the leakage rate is exceeding acceptable limits. If this is not sufficient to keep the leakage under control it must, depending on the nature of the cargo, be considered to discharge the tank using the portable pump. Cargo leakage to cofferdam normally indicates shaft seal leakage. But the leakage might come from flange connections or damage (cracks/pin holes) in pump/pipe stack (ref. chapter 4, Trouble shooting). The development of a cargo leakage can be monitored if purging is done according to instructions. Thereby maintenance work can be planned, and unexpected shut down due to leakage can be avoided.  

Hydraulic oil leakage 

Hydraulic oil in the cofferdam normally indicates shaft seal leakage, but might come from flange face seals in pipe stack/ pump head or damage in the pipe stack/pump head. A small leakage rate into the cofferdam up to about 10 ml/h (0.25 l/day) from the mechanical oil seal or lip seal during pump operation is normal. For short periods of time, higher leakage peaks can occur. If the leakage rate is increasing above acceptable level, the pump must be purged a couple of times daily, and inspected at first opportunity to find the reason for the leakage. Intensify the purging if the leakage rate is increasing above the acceptable level. If this is not keeping the leakage under control, close the hydraulic service valve. Depending of the nature of the cargo consider to use the portable pump to discharge the cargo.