Strainers · Continuous Duty

Duplex strainers

Two straining chambers served by a single changeover valve. Flow is directed through one basket while the other is isolated, opened and cleaned, after which the duty is transferred without interrupting the line. Specified wherever the cost of stopping the process exceeds the cost of the second chamber.

Changeover is ordinarily effected by a three way transflow valve of our own manufacture, which allows the valve and the strainer bodies to be engineered as a single assembly rather than assembled from separately procured components.

Request a quotation View specification

Flair twin basket duplex strainer with three way transflow valve

Photograph of completed unit
Duplex Strainers

Changeover Arrangement

One valve, two chambers, no interruption

Three way transflow valve Standard

A single valve carries flow across both chambers, and the changeover is completed in one movement. The transflow port maintains flow throughout the transition rather than interrupting it at mid travel.

Twin valve arrangement Larger bore

Individual inlet and outlet valves on each chamber, applied where the line size, pressure rating or material selection makes a single changeover valve impractical.

Operation Manual or actuated

Lever operated as standard, with gear operation on the larger sizes and pneumatic or electric actuation where remote changeover is required.

Specification

Standard range

Where a stated range does not cover a particular requirement, equipment is engineered to the customer specification.

Size range	25 mm to 400 mm
Construction	Twin chamber, cast or fabricated
Design code	ASME Sec VIII Div 1 on fabricated units, IBR on request
Filtration range	Coarse to medium
Element type	Perforated sheet, mesh lined perforated sheet, wedge wire
End connections	Flanged, screwed, socket weld or butt weld
Changeover	Three way transflow valve or twin valve arrangement
Operation	Lever, gear operator, pneumatic actuator or electric actuator
Options	Differential pressure gauge across both chambers, individual drain and vent connections, pressure equalising line, lifting davit, jacketing

Materials of Construction

Grades routinely handled

Carbon Steel SS 304 SS 304L SS 316 SS 316L

Alloy and duplex grades are quoted against the process fluid. Valve body material is ordinarily matched to the strainer bodies so that the assembly presents a single material specification for certification purposes.

Applications

Where these units are installed

Continuous transfer and circulation lines that cannot be isolated Pump suction protection on duty and standby sets running continuously Fuel oil supply to boilers, engines and turbines Lubricating oil and seal oil systems serving rotating equipment Utility water services feeding critical plant

FAQ

Common questions

Is flow interrupted during changeover?

No. The transflow port is profiled so that both chambers are open to the line through the middle of the travel, which carries flow across the transition rather than closing it at mid position. Where a pressure equalising line is fitted, the standby chamber is brought up to line pressure before the transfer, so the changeover produces no pressure surge either.

What is the difference between a duplex strainer and a duplex filter?

A duplex strainer carries twin baskets on coarse and medium retention duty. A duplex filter is configured to accept basket, cartridge or bag elements according to the required cut point, which extends the same changeover arrangement to fine filtration. See our duplex filters where the duty calls for a defined micron rating.

Can the changeover be actuated?

Yes. Lever operation is standard, with gear operation on the larger sizes, and pneumatic or electric actuation where the changeover is to be made remotely. Limit switches are fitted for position indication back to the control room.

How is the cleaning interval determined?

By differential pressure across the chambers. A gauge reading across the duty chamber indicates when the element has accumulated enough solids to warrant changeover, which is the operative signal rather than a fixed schedule.

Enquiry

Request a quotation for Duplex Strainers

Give us the line size, flow rate, fluid and operating conditions and we will engineer directly against them. Most enquiries are answered the same working day.