There’s a major misconception about the word filters when it comes to marine engineering equipment. As an equipment which carries out filtration is called as a filter but indeed this word is a misnomer and this may appear legit when you understand the concept behind it.
Filters and Strainers – What is the difference?
Filters and strainers both substantially filter out the contaminants in fuel oil, lubricating oil and water onboard a ship but there’s a fine line of difference between filters and strainers as the latter are installed on the suction side of the pumps to prevent the contaminants, debris or foreign matter from entering and damaging the running parts of the pumps.
Strainers are generally of the full flow type and hence their application is entirely different from the filters.
Filters on the contrary are fitted on the discharge side of the pumps and could be of the full flow or by-pass type.
The media filtered is generally the foreign particles or contaminants which are diminutively small and are unable to be filtered when in circulation.
A clean strainer causes a drop in pressure in the line which could be attributed to the rate of flow, the viscosity of the fluid being filtered, the size of the filter and the size of particles being removed.
There is a distinct type of filter called as auto back filter which works on the principle of pressure drop before and after the filter. The auto back wash filter cleans itself when the pressure drop increases beyond a certain value by blowing back air from outside to inside.
These filters could be of various types mainly simplex filters, duplex filters, by-pass and full flow filters.
A simplex filter is a simple basket filter which is fitted in the line; a duplex filter is arranged in a pair and hence one filter could be used and the other could be cleaned and kept as stand-by; a bypass filter takes a part of the fluid from the line, filters and returns it back to the suction side of the pump; while a full flow filter takes the complete amount of discharge from the pump for filtration.
Read more: What Are Magnetic Strainers And Filters?