FACTORY TRAINED OTJ EXPERIENCE ENGINEERING SUPPORT
How to Compare and Select Cast Simplex Strainers
Avoid the pitfalls related to relying on only size
By: Chris Pasquali; President & CEO of Factory Direct
Pipeline Products, Inc.
Cast vs. Fabricated Simplex Basket Strainers
Cast and molded simplex strainers have a fixed ratio
of cross-sectional inlet opening to basket-surface area whereas custom
fabricated simplex basket strainers can be designed for higher straining
ratios. The open area ratio (OAR) takes into account the open area of
the basket for which the fluid passes through with mesh lined baskets
having less open area than perforated baskets. You can use the OAR to
quickly identify strainer designs which might require less frequent
Cast strainers are mass-produced in foundries located in other countries
where environmental regulations are less stringent and both material and
labor costs are minimal, causing them to be significantly less expensive
than custom fabricated basket strainers. Often cast simplex basket
strainers weigh 80% or less than comparable fabricated simplex basket
strainers because the molds used by foundries enable thinner wall
thicknesses; this characteristic also reduces material cost and is an
advantageous feature when installed on portable equipment.
Foundry tooling for cast strainers is expensive to design, maintain and
modify which is why fabricated strainers are used when custom nozzle
orientations, additional ports/connections, a thicker walled design,
higher straining ratios or other such customizations are required.
Cast Simplex Basket Strainer Designs: Internal Geometry and Ergonomic Features
When a cast strainer is appropriate for an application it is commonplace
to simply search for a strainer size equal to the pipeline it will be
installed, matching the strainer material to that of the pipeline; often
cost and availability become the primary selection criteria. Have you
ever wondered “Why is there such a variation in cast simplex basket
strainer pricing for a given size and material?”
Several Aspects to Compare Before Deciding
The basket design is a process related aspect to consider because it directly
relates to the efficiency of the strainer design.
It is advantageous for some applications to have a strainer basket as
large as possible for a given pipeline size because it maximizes the
surface area available for particle retention, increasing the interval
between basket cleaning. The importance of that aspect varies with each
application; if your application is a batch process then the strainer
basket only needs to be of sufficient size to make it through that batch
at an acceptable differential pressure. If there is potential for an
upset condition and lots of particulate or there is a desire to minimize
plant personnel exposure to the process fluid, a larger strainer basket
Some strainer baskets have a slanted entrance ring
and others are tubular with flow passing over the “top”; whether there
is an advantage to either style is application specific. If your
pipeline velocity and particle load is low or your fluid is shear
sensitive, a slanted basket design might offer better performance.
The design of a cast simplex strainer dictates the design of the strainer
basket. You can compare simplex basket strainer designs without comparing
the surface areas of baskets by referring to the strainers flow coefficient
The Cv is a measurement of the
flow resistance for a particular strainer design. When comparing
simplex basket strainer designs, a higher Cv value indicates it is
capable of handling a given flow rate with less restriction (pressure
drop). The difference in Cv values is a reflection of the internal
finish and geometry of the strainer body which happens to dictate the
size and design of the strainer basket.
Just because “model A” has a Cv value higher than “model B” does not necessarily
mean it will perform better. While a larger strainer basket is associated
with a higher Cv value and can retain more material before requiring cleaning,
much depends upon your flow rate and particle load.
If your flow rate is low for the pipeline size (a fluid velocity ≤ 5 FPS) the
difference in flow resistance will likely be negligible. Likewise, if
strainer baskets are cleaned based upon schedule and not only at high
differential pressures, a design with a lower Cv would be functionally
The following screen capture of our web-based
differential pressure calculator compares (6) 8” 150# flanged cast steel
simplex strainer models based upon user input application information.
Even though 4 of the 6 strainer models have the same Cv, the variation
in pricing is significant and this is a reflection of the difference in
As an example, the 510 has a special low-to-the-floor, multi-basket
design. Its straining ratio is the highest of all the strainers listed
and the multi-basket design eliminates the need for overhead lifting
devices. If you are only shopping for the lowest cost, you might not
even realize that such a design exists!
Strainer chamber covers can be secured to the strainer body with studs/nuts or a
“quick opening” style that does not require tools to open the basket chamber,
such as a yoke style clamp, swing bolts or knobs.
The design pressure for the strainer dictates which closure styles are
applicable. A quick-opening cover design increases the convenience and
reduces the labor time required to clean the strainer basket. However,
this might not be a desirable feature for applications involving very hot or
otherwise hazardous fluids.
Some manufacturers include threaded taps for differential pressure measurement
and a vent valve while others charge an additional cost for these features.
Such aspects are often overlooked but should be considered for a thorough
Venting the strainer basket chamber with a needle
valve enables a slow and controlled release of vessel pressure as well
as drainage of the strainer basket chamber. This is especially
important when the process fluid is hazardous.
A pair of pressure
gauges or an actual differential pressure gauge (available with switches
and transmitters), measures the differential pressure across the
strainer basket as an indication of clogging. If the differential
pressure exceeds 15 to 20 PSIG there is increased likelihood of strainer
basket damage. Ideally you want to clean the basket after the
differential pressure increases by 5 PSIG above the initial “clean”
differential pressure, which would indicate up to a 75-80% clogged
There are many factors that to consider prior to selecting a simplex
basket strainer that are not easily discerned with online searches based
solely on size or price. Our company has nearly 30 years of experience
and training in the application of pipeline strainers enabling us to
provide valuable advice in support of choosing the best strainer design
for your specific application.
Once we have settled on the “best” strainer design for your specific application
we can assist with providing the accessories you might need such as differential
pressure gauges with or without switches and vent/drain/isolation valves that
are compatible with your process.
pioneered interactive sizing tools based upon fluid velocity and
differential pressure to assist with selection of pipeline strainers,
contact us to take advantage of the additional assistance we provide to
you at no cost or obligation. This is our core field of expertise and
we will quickly provide a recommendation, saving you time otherwise
spent researching things yourself online.
Chris Pasquali has been trained by
Hayward Flow Control and Eaton Filtration, having provided sales and
engineering support since 2001.