Duplex Basket Strainer

Size: 2" - 24" (DN50 - DN600)

Pressure: Class 150 - 300 / PN 10-40

Standard: MSS SP-89, manufacturer-specific for duplex strainers

Body Materials: A216 WCB (cast carbon steel), A351 CF8M (cast stainless 316), A351 CF8 (cast stainless 304), ductile iron (GGG40)

Straining Element: Perforated screen or mesh-lined basket. Screen perforation 0.5mm - 6mm. Mesh 20 - 200 mesh. Basket material matches body.

Design: Two parallel chambers with diverter valve (plug or ball). Continuous-flow operation — zero line shutdown for basket maintenance.

Why Two Chambers Matter

Some lines just can't stop. Chemical processing plants running continuous reaction loops — you shut the feed line for thirty minutes to clean a strainer basket and the whole batch is compromised. Power plant cooling water circuits pulling from rivers and lakes — debris loads spike after storms and that single basket strainer clogs fast, but the turbine doesn't pause because the strainer needs cleaning. Refinery fuel oil circulation, offshore seawater injection — these systems run around the clock because stopping them costs real money or creates real hazard.

That's the entire reason duplex strainers exist. One chamber handles the flow. The other chamber sits isolated, waiting. When the active basket fills and your pressure differential starts climbing, you don't shut anything down. Turn the diverter valve. Flow shifts to the clean chamber in seconds. The dirty chamber is now isolated — open the cover, pull the basket, clean it, put it back, close the cover. The line never stopped. Production never paused.

Inside the Diverter Valve

The diverter valve is what makes a duplex strainer work, and the choice between plug and ball matters more than most spec sheets admit.

Plug valve diverters give you tight shutoff between the two chambers. The plug seats hard against the body — metal-to-metal contact that seals reliably even when debris is present in the flow. But turning a plug valve takes more force, especially at larger sizes. If you're specifying a manually operated duplex strainer above 8" with a plug diverter, the operator needs leverage. That means longer handles, more physical effort, and in some installations you'll want an actuator instead of a handwheel.

Ball valve diverters turn easier. A quarter-turn and you've switched chambers. The force requirement is lower, which makes ball diverters popular on manually operated units. The tradeoff is sealing. Ball-to-body contact does the isolation between chambers, and in dirty service — abrasive particles, slurry, high-debris loads — that sealing surface can wear. It's not a failure, it's a gradual degradation. The chambers start to leak into each other and you lose the clean isolation you need for safe basket removal.

Either design works. The question is what's in your flow stream and how you want to actuate the switch. Clean water service with occasional debris — ball diverter, easy turn, perfectly adequate. Heavy debris loading or abrasive media — plug diverter, tighter seal, more turning force. Size above 12" and you probably want actuated switching regardless of valve type.

Size and Cost Reality

At sizes above 12", duplex strainers get expensive fast. Two full-size cast bodies, a diverter valve mechanism machined into the connecting passage, four cover assemblies, and all the internal basket seating. You're buying two strainers bolted together with a switching mechanism in the middle — and that's exactly what the price reflects. But for applications where a single basket strainer's periodic shutdown is unacceptable, the duplex is the only continuous-filtration option at process-line scale. There's no cheaper alternative that gives you uninterrupted flow with basket access. The duplex strainer costs more because it solves a problem that can't be solved any other way.

Yes, but the diverter valve orientation matters. Vertical installation with flow going upward — make sure the diverter valve shaft is horizontal so gravity doesn't bias the valve position. Vertical downward flow works too, but you need to confirm with the manufacturer that the basket seating design handles the reverse-flow load direction. Most standard duplex strainers are designed for horizontal installation; vertical installs are possible but require layout review.

Pressure differential. Install a DP gauge or transmitter across the active chamber. When the differential hits your set threshold — typically 5-15 psi above clean-basket baseline, depending on your flow conditions — that's your switch point. Some operators switch on a time schedule instead, but pressure differential is the reliable indicator because debris loading varies with actual conditions, not with your calendar.

They should be. The two chambers alternate — if chamber A has a 40-mesh basket and chamber B has a 100-mesh basket, you're getting inconsistent filtration every time you switch. Same mesh, same perforation size, same basket design in both chambers. That way the product quality downstream doesn't change when you flip the diverter valve.

Depends entirely on your debris load. Light debris in clean water service — you might switch chambers once a week. Heavy debris in river water or process slurries — multiple switches per day. The point of the duplex design is that maintenance frequency doesn't dictate process downtime. Clean the basket whenever it needs cleaning. The other chamber keeps the line running.

Yes. Electric or pneumatic actuators mount on the diverter valve shaft. Automated switching tied to a DP transmitter lets the strainer switch chambers without operator intervention — the DP signal triggers the actuator, flow shifts, the dirty chamber waits for manual basket cleaning. Automated duplex strainers are common in unmanned installations and remote process stations where operator access is limited.