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How to
Choose a Basket Strainer
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| 1 |
Why
Open Area Ratio is Important |
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| The
open area ratio in basket strainers refers
to the amount of free open of the strainer and basket. It is the ratio
of the open area through the strainer basket to the cross sectional area
of the pipeline. A well designed basket strainer should have an open ratio
of at least 4 to 1. Anything less may cause excessive pressure drop. The
ratio is calculated with a clean basket and as the basket begins to clog
the ratio will drip. Unless there is a wide safety margin the area through
the basket may quickly become smaller than the pipe area. This will reduce
flow through the strainer and necessitate very frequent cleaning. A small
open area ratio also means the holding capacity of the basket is small
- an important consideration if the amount of solid matter to be removed
is large. |
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| 2 |
Access
to the Basket |
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| A second
consideration in strainer selection is ease of basket
removal. Since a basket strainer is used where cleaning may occur often,
it stands to reason that the basket should be able to be removed and replaced
as simply as possible. A yoke type cover will accomplish this. The strainer
cover is held down by a clamping yoke which is sturdy enough to hold full
line pressure and yet, which can be quickly loosened or tightened by hand.
Bolted covers are also furnished with basket strainers and they cost less
than yoke covers. However, every time they are handled their nuts must
be taken off and replaced the same as with a flange. This is time consuming
and, in the long run, expensive. |
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| 3 |
Other
Things to Look For |
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| Another
item to look at in picking a strainer is compactness
of design. Is the strainer unnecessarily bulky or tall? In many industrial
areas space is at a premium and the less room a basket strainer takes the
better. This is especially true on board ships where every square foot
counts.
A wide variety
of basket perforations and mesh sizes should be available. This is necessary
to cope with the great range of particle sizes which the sterner may be
called upon to remove. |
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| 4 |
Materials
of Construction |
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| A
basket
strainer should be available in several materials
of construction, the same as valves. A good manufacturer should offer basket
strainers made of iron, bronze, steel, and stainless steel. Iron, of course
is the least expensive. Bronze and steel cost about twice as much as iron
and stainless steel costs about four times as much. |
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| 5 |
Iron |
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| Since
it costs, the least, iron should be the first choice of a
basket strainer user, and for this reason it is by far the most popular
material. Cast iron has good corrosion resistance in water service. It
is also used with many non-aqueous materials such as paint, fuel oils,
and plastics. Iron strainers are generally supplied with brass or stainless
steel baskets. The disadvantages of iron are its inability to stand thermal
or mechanical shock plus tits susceptibility to corrosion in many applications. |
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| 6 |
Bronze |
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| Bronze
is the preferred material for marine service. Bronze strainers
are widely used for handling sea water and also brackish or saline ground
waters. The best basket material in these areas is Monel. Stainless steel
will not resist sea water as well as Monel. Another use for bronze strainers
is where the product can be contaminated by iron, but the cost of stainless
steel is prohibitive. A good example is handling of liquid sugar. The material
is sensitive to iron pickup. Stainless steel is expensive. Bronze is a
good compromise and is therefore used. Bronze can also be used with mildly
corrosive materials where iron is unsatisfactory and stainless might be
too costly. |
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| 7 |
Carbon
Steel |
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| Carbon
steel strainers are used mainly in the oil and petrochemical industry.
They have excellent resistance to mechanical or thermal shock and these
are important considerations in the event of a fire. Most oil refineries
will not permit iron piping components for this reason. Steel strainers
are also used for higher pressure applications because of their great strength.
Basket material is generally stainless steel. |
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| 8 |
Stainless
Steel |
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| Stainless
steel strainers, of course, are used where high corrosion resistance or
where freedom from contamination are required. They are popular in the
chemical, food, and pharmaceutical industries. Naturally, stainless steel
strainers should have stainless steel baskets. |
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to Hayward Back to PEP
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Copyright
HAYWARD Industrial Products, Inc. 1999
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How
to Choose a Basket Strainer