Chemical Engineering October 2016 - 63

capital expenditures and protect the
operation's bottom line.
With all that being said, bayonetand-plunger
couplers do have several
operational characteristics that
can potentially limit their optimal
application in chemical manufacturing
settings. First, while an extremely
small amount of fluid may
be lost during disconnection, there
are other coupler technologies that
have been proven to lose less fluid.
From an operational standpoint,
the biggest shortfall of bayonetand-plunger
couplers is their internal
design, which puts a number of
parts in direct contact with the fluid
flow. Any type of flowrate restriction
will negatively affect the production
process. For example, if an
engineer specifies a 2-in. line and a
bayonet-and-plunger coupler with a
2-in. I.D. is installed, the flowrate will
actually be less than what is to be
expected from a free-flow 2-in. line
because the liquid will have to work
its way around the coupler parts
that it comes into contact with. This
may also necessitate the installation
of a larger-than-necessary
2.5- or 3-in. coupler, which can be
more expensive.
Additionally, the
bayonet-andplunger
coupler's internal components
(things such as springs,
guides and poppets) can also create
areas where the liquid can collect
and nest, which makes it difficult to
clear the lines and maintain a clean
pumping environment. This is especially
true when handling liquids with
higher viscosities.
Bayonet-and-plunger couplers
can be at a disadvantage when
manufacturers choose to incorporate
a closed-loop fluid-transfer
system. The drawback is that in a
closed-loop system, there may be
numerous valves deployed, meaning
that, at some point, the closing
of two valves will leave product
trapped in the hose between the
closed valves. The pressure that
is created when the downstream
valve is subsequently opened has
the potential to damage the drydisconnect
coupler
downstream
of it, which can lead to leaks and
product spills.
Lastly, bayonet-and-plunger couplers
are harder to repair or maintain
inline because of the number
of parts they contain. In fact, many
bayonet-and-plunger suppliers require
the coupler to be removed
and returned to the manufacturer
for repairs. If the coupler can be
repaired in the field, the number of
steps in the repair process, along
with the number of parts to consider,
can make it difficult or confusing
for the maintenance technician,
which could result in a repair job
that leaves the coupler vulnerable to
less than optimum operation and an
increased risk of leaks or spills.
Circle 37 on p. 78 or go to adlinks.chemengonline.com/61500-37
58
Double ball-valve couplers
In addition to bayonet-and-plunger
dry-disconnect couplers, an emerging
coupler technology is the lowspill
dry-disconnect coupler (Figure
2) that operates via a double
ball-valve design. This technology
features a convex ball that rests
in a concave ball, resulting in the
elimination of any cavity between
the mating halves. This guarantees
that no residual fluid will be trapped
there, lowering the risk of spills and
giving the liquid virtually no place to
collect or hide, which eases cleaning.
The box on page 55 compares
the differing flow mechanisms of
double ball-valve and poppet-style
dry-disconnect couplers.
The double ball-valve design also
incorporates multiple safety interlocks
that allow the valve to open
and close only through a deliberate
action by the user. This prevents
any accidental opening of the valve,
which lowers the risk of unintentional
spills and catastrophic chemical releases.
This is not only critical when
transferring raw materials from large
storage vessels, but also during the
numerous tote-filling operations that
are a staple of chemical manufacture.
This constant on-and-off filling
of smaller-capacity containers can
put undue strain on the couplers,
but the double ball-valve design and
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
OCTOBER 2016
http://adlinks.chemengonline.com/61500-37 http://WWW.CHEMENGONLINE.COM
Chemical Engineering October 2016

Table of Contents for the Digital Edition of Chemical Engineering October 2016
