ASHRAE Journal - July 2022 - 54

COLUMN ENGINEER'S NOTEBOOK
PHOTO 3 Brass threaded and sweat wye strainers.
PHOTO 4 Cast iron wye strainer
38 mm]) blowdown line might overflow
the drain if it was open for very
long. (Remember, the blowdown
is under pressure, so a lot of water
can flow quickly). The installed
orientation of the threaded plug is
also important; it should be rotated
to the lowest possible point during
installation, because that is where
dirt, rust flakes and other gunk will
settle.
Wye vs. Basket Strainers. A wye
strainer is a simple strainer, shaped
like the letter " Y, " that typically
includes a relatively small, low
capacity basket. The strainer body is
usually sized similar to the entering/
leaving piping. A basket strainer,
on the other hand, is physically
much larger (and heavier-important
if you are supporting it in suspended
piping) than the typical wye
strainer; a basket strainer is typically
in a vertical cylinder (think thermos
bottle) configuration.
The typical basket strainer has a
basket that has many times more
surface area than a wye strainer of
the same pipe size, offering lower
initial pressure drop and the ability
to catch a lot more material before
it needs to be cleaned. Because the
common wye strainer holds very little
debris/material, its only real purpose
in a closed loop is to protect at
start-up other components (control
valve, flow balancing/limiting valve,
etc.) from big chunks of stuff that
might have somehow gotten into the
piping during construction.
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A S H R A E J O U R N A L
as h r a e . o r g
In practice, there is seldom a good
reason for a strainer in a closed loop
copper piping system, other than
at the pump itself, since it would
take real effort to have something
lost in the pipe during installation
that is so big it was worth catching
in a strainer. In steel piping, there
might be enough welding slag to
cause an issue (or if threaded pipe
is used, you might find trash from a
threading machine). By and large,
a strainer at the pump inlet (with
a coarse mesh size) is what makes
sense in a closed loop, just to guard
the pump against rags, bolts, energy
drink cans or anything else that may
have been left in the piping during
construction.
Start-Up Strainer. It is common
for pumps to arrive with inlet strainers
(or suction diffusers that also
serve as inlet strainers) with two
strainers installed: the fairly coarse
strainer intended for lifetime use,
and a much, much finer interior
liner that rests inside the coarse
strainer. The intent is for the fine
liner to pick up the bulk of the stuff
that is circulating at initial start-up
and pipe cleaning. Then this liner
is removed as the last step prior to
water balancing.
I've lost track of the number of
times I've run into a start-up liner
J U LY 2 0 2 2
that had not been removed. Not only
does this result in an unnecessary
energy penalty, but it also fouls up
the water balance effort. Remember
that the end plate that holds in the
strainer basket has to be removed to
remove the start-up liner, and that
end plate has a gasket. One thing
that seems to help avoid this failure
to remove the start-up strainer is to
specify that an added set of strainer
gaskets ship with each pump. Field
techs are often reluctant to pull off
an inspection cap for which they
lack a gasket. If it turns out that the
original gasket did not tear and they
don't need the spare, the facilities
folks will be grateful for the extra
gasket-because they will certainly
need it at some point.
While discussing strainer gaskets,
there is another very practical thing
to recognize. For open loop pump
inlet strainers, blowdown will only
go so far to clean the basket, and
eventually it is necessary to remove
the plate that holds the basket to
remove it and clean it. Finding the
right gasket for that plate years after
installation can be maddening-
another reason to specify that extra
set of inlet strainer gaskets. And for
that reason, the gasket wrapping
(with part number) will be saved
and often nailed to the wall above
the pump, for future reference.
Deciding Upon the Right Mesh
What is the logic behind mesh
selection? Rule of thumb is to pick
a mesh sized to permit the biggest
particle to pass that is still somewhat
less than half the diameter
of the smallest orifice passage in
the heat exchanger, valve, etc. This
is so two individual particles that
can get through the mesh will be
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