Industrial filter can be provided with double-opening element (DOE) or single-opening element (SOE)

Double-opening element (DOE) is double-sealed. One of the sides is wound tight. DOE has a simple design and requires little capital, and is popular in environments where high-precision is not required and where the levels of impurities is not of particular concern. 
It is widely used in pre-filtration of a water filtration system to protect the membranes. They are also employed in filtering environments of high-temperatures such as food clarification and heat transfer oil production where the cartridges are made of fiberglass or bleached cotton

SOE has only got one opening and since it has only one seal, it is suitable for Double-O seal with no side leakages and is used in environments where the the filtration precision required is higher.

Classification: industrial (liquid) filter, industrial (gas) filter