A Y type strainer is installed in flowing medium systems and is designed to removed suspended objects from the flowing medium; the medium is usually a fluid, vapour or gas.
The medium flows into the strainer casing through the suction port, it then travels through a perforated cylinder and is discharged through the discharge port. The perforated cylinder is the strainer. Suspended object in the medium that are too large to fit through the perforations (holes/gaps) are retained in the strainer and often accumulate in the strainer pocket/base. The size of the suspended particles being removed from the medium depends upon the size of the strainer perforations.
The removal of objects from a system allows the system to remain in a constant condition e.g. no detrimental effects to downstream apparatus. Failure to remove objects from a system can lead to common problems such as pump damage, or, a reduction in the heat transfer rate of heat exchangers etc. (there are many other examples!).
Construction materials vary depending upon the system served. Systems with corrosive fluids e.g. seawater, will typically have bronze strainer casing's and stainless steel strainer's. Systems with reactive or extremely corrosive fluids may use polymer based materials e.g. PVC. Strainer construction materials should be chosen carefully as the wrong choice will often cause the strainer to fail (either suddenly, or, progressively over time).
A Y strainer constructed for a high temperature, high pressure, steam system, can be constructed from suitable alloys such as chrome molybdenum steel.
Y Strainer Applications
Applications are numerous due to the strainers simple design and easy maintainability. The strainer can also normally be repaired locally without requiring expensive equipment or advanced technical 'know-how'. Spares (partial or entire) are normally readily available and cheap.
There are three main types of Y strainer, these are coarse, medium and fine. Y strainer's are generally used for medium or fine filtering. Y strainers do not have the same filtering capacity as basket strainers and often require more frequent cleaning.
Y strainer's can be used at pressures in excess of 400 bar(g) although there are some limitations for steam systems due to the temperature. It is not uncommon for a blow-down valve to be installed, this allows the Y strainer to be cleaned with steam in a similar manner to a basket strainer being blown-down with compressed air.
A Y strainer can be installed at any orientation, but this does not mean it is installed correctly. For gas or steam systems, Y strainers should be installed horizontally to prevent water accumulating within the strainer pocket. For liquid systems, the pocket should always point downwards as this will ensure trapped materials gather in the bottom of the strainer pocket and do not block the suction and discharge ports. It is possible to install the strainer vertically, but it is only installed correctly if the flow is in the downwards direction and the strainer is mounted with the pocket downwards.
What is the difference between a strainer and a filter?
The two terms are often used intermittently although technically a filter refers to a disposable object which when cleaned is not restored to its original state. A strainer is disposable but can be cleaned in order to restore it to its original condition (and is thus not disposed of!).