Basket strainers are a device typically connected to a pumps suction, which is used to filter out solids or debris larger than the mesh contained within the strainer, which would otherwise damage the pump, internal parts or system. They are used to capture particles which are usually visible to the naked eye, and if smaller, filters are typically used.
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Strainer Vs Filter
Used to capture larger solids visible to naked eye
Used to capture particles invisible to naked eye <40 microns which may include salts, or carbon particles
Designed for a single type of fluid
Can capture different fluids such as water within oil
Lower pressure drop enabling use of low pressure designs of pumps
Require high pressure pumping involving high powered positive displacement or multistage pumps which if selected incorrectly will experience rapid wear by the handling of such particles
Filter mesh is designed to be reused over many years
Can be single use or reused through the use of backwashing
Designs consist of a suction inlet, discharge outlet, bolted top cover and casing. The casing holds a filter typically manufactured from wire mesh designed to filter solids which become trapped by the mesh, and sink within the casing. Top covers can be clear or solid. Housings may have a drain at the bottom of the casing where solids will sink to enable them to be drained away.
There are various designs known as Y Type, Simplex, Duplex or Backwash.
This type of design is the most economical type which can be mounted horizontally or vertically and is compact in design. Other designs can typically only work horizontally.
They are cast in one piece, meaning they usually have a higher pressure rating tolerance. However due to their design, they produce a larger pressure drop than other variants.
Simplex models are designed for larger pipework, are longer and wider in design containing a significantly larger basket with removable lid for ease of maintenance.
Due to the larger surface area they are designed for capturing larger amounts of solids, and produce lower pressure drops. They can only be installed horizontally, but are easy to inspect and maintain without drainage of pipework.
Duplex models are very similar to simplex strainers in design, however contain two filter baskets which can operate simultaneously or separately. Having twin filters ensures processes can run interrupted whilst they are maintained, as one can continue to function, while the other is maintained.
Self cleaning strainers, also known as backwash filters or automatic strainers consist of a strainer, drain, scraper and motor.
Within the strainer there is a hollow shaft with a blade which when the cleaning process is initiated, scrapes along the inside of the mesh removing debris. Simultaneously a bottom outlet valve opens creating an area of low pressure causing the recently freed debris to flow via the bottom outlet valve and be drained away.
The cleaning process is initiated either by a timer, which starts the motor located at the top of the unit to begin the screening process or via a differential pressure switch which senses when the screen is blocked.
Pressure switches are located on the inlet and outlet of the unit and when the inlet pressure is higher than the outlet pressure, the filter is known to be blocked.
These are low maintenance designs enabling the mesh to remain clean and free from solids with long maintenance intervals, without manual intervention.
Y Type
Advantages
Simplex Strainer
Advantages
Duplex Strainer
Advantages
Backwash / Auto cleaning
Advantages
Mounted Horizontally or Vertically
Maintain without draining pipework
Mesh can be cleaned without Process Stoppage
Autonomous self-cleaning
Compact in design
Lower Pressure Drop
Redundancy / Spare Capacity in Design
Zero process stoppage
Economical
Higher Solids Capture
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Disadvantages
During Cleaning as the strainer is at the lowest point, there is a larger loss of fluid and system may need to be drained
Process must be stopped during cleaning
Bulkier in Design
Large units requiring piping to drain, which may require secondary filtration or dewatering
Higher Pressure Loss
Only Work Horizontally
Only Work Horizontally
Higher Initial Outlay
Pressure Loss
Below is a graph indicating single and double Basket strainer Pressure drop compared with Y type designs:
At a flow of 10M³H, (166L/min) the pressure drop on the basket type is only 0.3 bar, compared with 0.4bar (40KPA) for a 1" (DN25) Type
Single Basket vs Y Type Pressure Drop
Pressure Differential Indicator - This measures the pressure within the unit and when calibrated can detect high casing pressure, or higher inlet pressure signifying that the strainer mesh is blocked and requires cleaning.
Heating Jackets / Insulation Jackets &#; If material being filtered has a viscosity which changes with temperature then a heating jacket may be required to prevent solidification within the unit. Similarly, if strainers are subject to excessive heat from process such as within a steam process then an insulation jacket maybe required to ensure heat stress is not experienced by the unit unequally during operation.
Magnetic Filters &#; These are used to capture fine metal particles which may be present within the liquid and so fine they are unable to be detected by metal detectors. They are captured by magnets, and used within the food industry to ensure hygiene, and in the paint industry to prevent the formation of black specks within paint.
Air Eliminator &#; Typically designed to sense air and remove before liquid flows through a flow meter to ensure accuracy in a process or prevent issues further downstream of process.
View our Range of Models
Strainers remove debris from the flow to reduce the risk of damage to equipment such as pumps, chillers, and boilers. Suction diffusers are a specialized type of strainer used for direct attachment to specific pumping-equipment inlets where compact and accessible pipeline straining is needed.
Strainers provide a means of mechanically removing solids from flowing fluid by using a perforated metal, mesh, or wedge wire straining element. They protect downstream mechanical equipment such as heat exchangers, pumps, meters, and steam traps from the detrimental effects of sediment, rust, pipe scale, or other extraneous debris.
The most common configurations of strainers are wye (Y) and tee (T).
Y-strainers have a Y-shaped body with a strainer basket oriented at an angle. This design promotes debris flow out of the main water flow path for less obstruction and pressure drop during operation. Vertical piping, frequently found at the pump inlets, necessitates the use of a Y-strainer. A Y-strainer in vertical piping must be placed with its screen downward to trap the sediment in the debris collection chamber.
Tee strainers feature a T-shaped body that orients the strainer basket 90° to the main flow. Tee strainers provide excellent flow characteristics and are typically lighter and more economical than wye strainers. Strainers can have either grooved or flanged ends.
Most basket strainers are intended for horizontal or slightly inclined piping. Special attention should be given to the orientation of the debris collection chamber and the drain or blowdown. Refer to the manufacturer&#;s installation and operating manual for specifics. The strainer must be installed at the lowest possible position.
Magnetic strainers are an effective solution to the problem of excessive and premature wear to pump seals and wear rings. A standard strainer is fitted with magnets which are removed for cleaning. These magnets are spaced and arranged to create a magnetic field around the screen&#;s interior and attract fine ferrous (magnetic) particles, which could damage downstream equipment.
Regardless of the type of strainer used, they all essentially function similarly. A bonnet allows access to the strainers for cleaning and can be grooved or flanged/bolted. The bonnet is tapped and fitted with a ball valve to allow draining and &#;blowdown.&#; Blowdown is the process of opening the ball valve during operation to expel debris while the system is in operation. Blowdown is not a recommended substitute for complete removal and cleaning (&#;mucking out&#;) of the basket but can periodically assist performance.
Suction diffusers are a type of strainer. They are a combination elbow, reducer, strainer, and straightening vane that works to provide maximum flow efficiency at the suction inlet of the pump while at the same time reducing space and fitting requirements. In addition, they remove large particulates from water and process liquids to prevent damage to pumps or other system components. Suction diffusers are found in many commercial and industrial applications.
Read our previous blog post: What is a Suction Diffuser?
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