Strainer is a device which provides a means of mechanically removing solids from a flowing fluid by utilizing a wire mesh or perforated screen.
Strainers are used in piping systems to protect downstream equipment's such as pumps, turbines and compressors from damage.
TYPES OF STRAINERS
Temporary Strainers
- Conical strainers
- T-type strainers
- Disc or Plate type strainers
Permanent Strainers
- Y-type strainers
- Basket strainers
- Duplex strainers
- Cartridge strainers
- Self-cleaning strainers
TEMPORARY STRAINERS
Conical strainers
Conical Strainers are used in steam, water, oil or gas service, and are installed between two flanges for protection of downstream equipment. They are used either temporarily, or where cost is of prime importance. The pipe must be disassembled to inspect, clean, or remove these strainers. A conical strainer is installed with the tip of the cone facing the direction of flow. Conical strainers are designed to collect debris around the outer edges of the cone because this is a mechanically stronger orientation.
T-type strainers
T-strainers are compact and used in applications where space is restricted. The standard T-strainer includes a screen suitable for high pressures, which is easy to maintain and replace and capable of filtration of more than 200% of the inlet area. Filter elements are made of stainless steel perforated sheet or wire mesh supported by perforated sheet. Tee Type Strainers are a low cost solution to large nominal bore straining requirements. This strainer can be easily installed and requires minimal maintenance. Tee strainers are provided with either bolted cover or quick opening covers for application suitability. T Type Strainer can be used in both vertical and horizontal installations.
Disc or Plate type strainers
Where space restrictions exist, the plate strainer may be used. Low net open areas are available with this type of strainer. In addition, operating pressure drops are normally higher and maximum allowable pressure drops lower than other types of strainers..
PERMANENT STRAINERS
Y-type strainers
Y-type strainers are typically used in applications where the amount of solids to be removed is small and where frequent clean out is not required. They are most often installed in gaseous services such as steam, air, nitrogen or natural gas. They can be used in both vertical and horizontal installations.
Basket strainers
Basket strainers are commonly used in applications where larger particulates are present and requires frequent clean-outs. Basket strainers offer top removal of the internal screen. The internal perforated basket features a handle at the top for easy removal and disposal of all the particulate that is collected.
For applications where continuous operation is required and the line cannot be shut down, duplex or twin basket strainers can be used. When one basket becomes full, the flow is switched to the other basket. The first basket is removed, cleaned and replaced.
Cartridge strainers
Filter elements made of perforated sheet or wire mesh are best for removing particles as small as 40 microns. Their advantage is that they can often be manually cleaned and reused. Disposable cartridge strainers can remove contaminants down to about 0.1 micron. Additionally, carbon filters can be extremely valuable for treating feed water that contains organics, pesticides or chlorine-containing compounds
Self-cleaning strainers
An automatic self-cleaning strainer is a unit which goes through a complete cleaning cycle, using some of the fluid flowing through the strainer to flush out the collected debris, with little or no attention by the plant personnel. Self-cleaning strainers are particularly effective in fluid applications where unattended service and uninterrupted flow are required. Solids are captured in the strainer screen and are removed when the strainer backwashes. Downstream flow is not interrupted during the backwash cycle.
The capacity ratio, or open area ratio (OAR) of a strainer influences operating characteristics such as the length of time it can operate without cleaning and the created pressure loss. OAR is the relationship between internal cross sectional area (flow area) of the pipe and the open flow area of the material which makes up the straining element.
Open Area Ratio (OAR) = (100 x Mesh Open Area x Screen Area)/(Internal cross sectional Area)
Larger OAR’s are recommended for flow in which larger amount of debris is expected to be strained or where very viscous fluids are being handled.
As a strainer becomes clogged to the point where the OAR of the strainer approaches the pipe area, the pressure drop across the strainer increases very rapidly. At this point, it is recommended that the strainer be cleaned to avoid a large pressure across the strainer element.
