Custom fabricated duplex strainers are used when cast versions will not suffice. Sometimes special alloys are required or there are other aspects of the application just not suitable for cast duplex strainers, so we custom fabricate a duplex strainer instead.
Fabricated duplex strainers consist of two fabricated basket strainers having their inlet and outlet nozzles located on the same side. The two basket chambers are connected to an inlet and outlet pipe tee with valves. One set of valves are closed, causing the flow to pass through the other chamber. When it is time to clean the strainer basket, flow is diverted to the clean chamber and the dirty basket chamber is isolated so it can be safely accessed. The connections to the pipeline are typically ANSI flanged although can also be butt weld or some other connection as required.
There is a specific order to manipulate the diverting valves to ensure the process flow is not interrupted. First open the clean chamber discharge valve, then open the its inlet valve. Next close the discharge valve for the dirty basket chamber and then close its inlet valve. After venting the basket chamber and draining the fluid, the basket chamber can be safely accessed.
The type of valves used for custom fabricated duplex strainers are usually butterfly valves, although ball valves can be used if required. There are single, double and triple offset butterfly valves as well as 1, 2 and 3 piece ball valves; the valves used will depend upon the specific requirements of your application. It is possible to use a pair of 3 way diverting ball valves that are linked together to accomplish a similar diversion, however it is uncommon. It is also possible to install actuators to automate the sequence and eliminate manual manipulation of the valves.
The baskets for large fabricated duplex strainers might require an overhead winch or lifting mechanism. Optionally we can utilize a multiple basket design, so as an example, instead of using one large (heavy) basket, having four smaller baskets in the chamber - with each basket being easier to manually lift.
If your particle load is continuous and the pipeline 6" or larger, consider an automatic strainer which might cost the same or slightly less and provides the advantage of automatic operation without interruption of process flow.
For some applications we can supply a hinged "quick-opening" basket chamber cover design, which is especially useful for larger size strainers that would otherwise require a cover lifting davit assembly.
You can use our calculator above to approximate the clean differential pressure drop by selecting the strainer connection size, inputting your flow rate (GPM), inputting the specific gravity if other than water (sg of water = 1) and selecting the viscosity range if other than water (SSU of water = 30). Click "Update" to refresh the data and be sure that the clean differential is ≤2 PSI for the intended basket retention.
Sometimes to attain the desired clean differential pressure a larger size strainer body is required, and since these are custom fabricated, attaching smaller connections to match your pipelines is not a problem.
Custom fabricated duplex strainers typically have a engineering and manufacturing lead time ranging from 6-12 weeks depending upon the degree of customization required and current shop load.
The part numbers for the Eaton model 950 duplex strainers are listed below. Link to Eaton model 950 fabricated duplex strainer specificaitons and IOM manual.