Duplex Strainer (Duplex Filter) Guide
How twin-basket duplex strainers provide uninterrupted filtration — clean one chamber while the other keeps the line in service.
A duplex strainer (duplex filter) uses two parallel filter chambers and a changeover mechanism so flow is never interrupted: while one basket filters, the other can be isolated, opened, and cleaned. This makes duplex strainers essential for continuous processes — fuel oil systems, lube oil, cooling water, and any line that cannot be shut down for cleaning.
Simplex vs Duplex Strainers
Selection Factors
- Mesh / perforation: select the opening size for the particle you must remove (e.g. 20/40/60 mesh or perforated plate)
- Open area ratio: aim for 3–5× the pipe area to limit pressure drop and extend cleaning intervals
- Body material: Cast Iron, WCB, SS304/SS316, or fabricated steel to suit the media
- Changeover: plug-type, ball-type, or twin butterfly/ball valve diverters
- Options: differential-pressure gauges/ports, drain & vent, magnetic inserts
Frequently Asked Questions
What is a duplex strainer?
A duplex strainer has two filter chambers and a changeover valve so flow can be switched from one basket to the other. This allows one basket to be cleaned while the other continues filtering, giving uninterrupted protection.
When should I use a duplex strainer instead of a simplex?
Use a duplex strainer on continuous or critical lines that cannot be shut down for cleaning — such as fuel oil to engines/turbines, lube oil, and cooling water. A simplex strainer is fine where the line can be stopped to clean the basket.
How do I size the strainer mesh?
Select the mesh or perforation to capture the smallest particle that must be removed, while keeping the open (screen) area roughly 3–5 times the pipe cross-section to limit pressure drop and lengthen the cleaning interval.
Need Duplex Strainers for a Continuous Process?
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