Q - What are some guidelines on the sizing and installation of fabricated suction
strainer in horizontal p ump?


A - A common practice is to install a conical-shaped strainer with minimum
surface area of 2-1/2 times the pipe flow area. Typical material is No. 12 mesh
steel reinforced on the inside of strainer with No. 2 mesh. Install the strainer with
its tip pointed against the direction of flow so that dirt will accumulate at the outer
edge, not at the center, of strainer. Install pressure gauges immediately before
and after the strainer. Or, use a differential pressure gauge across the strainer.
Clogging of the strainer will be indicated by a drop in the downstream pressure.

A - An European company I have been employed for 10 years has this practice -
the hole diameter in the strainer is kept at a maximum of 2/3 the solid diameter
that can pass through the p ump; the total surface area of the holes is 3 to 5 times
the surface area of the p ump suction; and a shorter strainer with bigger holes is
preferred to a longer strainer with smaller holes for the same surface area.
Suction strainers



Suction strainer is a protective device containing mesh to filter out dirt, debris, and
other solids that can clog an equipment such as p ump, pressure reducing valve
(PRV), check valve (CV), trap, etc. The solids are then cleaned out of the suction
strainer during routine maintenance.

The mesh size is selected based on maximum particle size that needs to be
filtered out. The smaller the particle size, the smaller is the required sieve
opening. Note that the mesh number is the inverse of its sieve size, the higher  the
mesh number, the smaller is its sieve opening. For example, a number 4 mesh
has a 0.185" sieve opening, whereas a number 14 mesh has a 0.046" sieve
opening.

Although it is ideal to filter out most of the unwanted solids in a liquid, it is not
practical to do this because a strainer causes a pressure drop in a system. The
bigger the mesh size (smaller sieve opening), the higher is the pressure drop. In
many applications some amount of solid is allowed to pass provided it is not
detrimental to a process, or damaging to an equipment.
Fabricated suction strainer. This design has no provision
for cleaning the strainer without removing it from the piping.
Examples of Y-strainer (left) and bucket strainer (right)
Q - What are the differences between Y-strainer and bucket strainer? Which is
better for petroleum service?

A - As its name implies, Y-strainer has the shape of letter Y. Its tail end allows
easy access to remove the solids and to clean the strainer. The strainer can be
mounted horizontally, or vertically.

Bucket type strainer has vertical cylinder, or chamber, larger than in Y-strainer.
The straining area is larger allowing for longer time between cleaning. The flow
is less hampered by debris so the pressure drop across it is less than in  
Y-strainer. Bucket strainer is preferred in larger diameter pipes, in services
where longer maintenance interval is desired, or where pressure drop has to
be minimized for NPSH reason. Bucket type strainer, also known as basket
strainer, is mounted horizontally.

Either type of strainer can be used in petroleum, chemical, petrochemical, and
in most industrial service.

Question:
How much pressure drop across a strainer will indicate it is time to clean it?
Related topic:
Suction pipe and suction splitter
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