Simplex Basket Strainers
There are two kinds of basket strainers, simplex and duplex. A simplex basket strainer is used where the line can be shut down for short periods to clean or change baskets. It becomes an integral part of the pipeline and all flow passes through it.

Duplex Basket Strainers
A duplex basket strainer can operate continuously and never has to be shut down for cleaning. The most popular and convenient type is, in reality, a specialized plug valve. A diverter plug is carefully fitted to the strainer body. It permits flow to pass either left or right. When one basket becomes full, the flow is shifted to the other one. The dirty basket is then removed, cleaned and replaced, ready for use again. Another, newer, type of duplex strainer utilizes a diverter cartridge in place of the diverter plug. This diverter cartridge diverts the flow through the strainer using balls and operates like a ball valve. This design’s main advantage is that their is no leakage from one strainer basket chamber to the other.

Large Size Duplex Strainers
A get larger, however, these types of duplex strainer design become unwieldy and impractical. In these cases a sliding gate valve arrangement is used to transfer the flow. The valve discs are actuated by a set of hand wheels. They are synchronized so when one basket chamber is being opened to receive the flow, the other basket chamber I being sealed off.

Obviously, duplex basket strainers are valuable in locations where it is impossible to shut off flow or stop the operation. Examples are cleaning fuel oil in large industrial oil burners, for all types of marine applications, straining water in cooling towers, and straining fluids in continuously running chemical operations.

Most people do not realize that a duplex strainer is useful in applications other than ones which must run continually. Often it is desirable to keep something going for a few hours only, but during this short time the line must not shut down.  In filling paint cans, for instance, there may be considerable variations from batch to batch. One lot might have an unusually large amount of material to be strained and the filling line would have to be stopped several times if a simplex basket strainer were used. A duplex unit avoids this. Flow can be switched from one basket to the other, as can fill, and the line can keep running.

An Important Consideration
An important feature of a well designed duplex basket strainer is that it must never allow the flow to stop. If this is possible, a careless workman can inadvertently do great damage. For instance, the flow of lubricating oil to a compressor could be shut off while switching from one basket to the other. With a properly made duplex strainer it should be impossible to stop the system. If this is required, a separate valve can be used.