Chemical Engineering July 2013 - 53

valves that are used to feed solids into
a conveying line are installed such
that the rotary valve and the line injector
below it are perpendicular to
the conveying line (Figure 8). A line
injector is used to connect the rotary
valve to the conveying line. Its design
is important because excessive turbulence
in this region has an adverse effect
on the performance of the conveying
system.
In pressure-type conveying systems,
any intermediate spool pieces between
the rotary valve and the line injector,
or between the line injector and the
conveying line, should not be used because
the resulting air turbulence can
adversely affect the flow of solids into
the conveying line.
The direction of rotation of the rotary
valve should be clockwise when
facing the valve, such that the conveying
air enters the conveying line from
the valve's left side.
Rotary valves in dense-phase pneumatic
conveying. Presently, rotary
valves used in dense-phase pneumatic
conveying are designed to withstand
differential pressures up to 6 bars and
maximum solids feed rates of about
5,000 ft3/h.
High circumferential
clearance leakage that occurs due to
these high pressures is minimized by
increasing the number of rotor blades.
Some good designs have as many as
24 blades.
Rotor-end leakage is prevented by
using a specially designed, gas-tight
seal between the rotor and valve body.
A well-designed venting system to
properly vent out the clearance leakage
air and the rotor carry-over air is
a necessity for these high-pressuredrop
rotary valves.
Rotary valves with special features.
Rotary valves are made with
special design features for applications
such as food grade installations,
those requiring quick and easy access
for cleaning, those handling corrosive,
abrasive or sticky materials, those
handling very high or very low solids
or ambient temperatures, but the basic
design principles described above still
apply to these designs.
n
Edited by Suzanne Shelley
Reference
1. Agarwal, Amrit, " Improving Rotary Valve
Performance, " Chem. Eng., March 2005, pp.
29-33.
Author
Amrit Agarwal is a consulting
engineer with Pneumatic
Conveying Consulting
(7 Carriage Rd., Charleston,
WV 25314; Email: polypcc@
aol.com). He retired from The
Dow Chemical Co. in 2002
where he worked as a resident
pneumatic conveying and solids-handling
specialist. Agarwal
has more than 40 years of
design,
construction, operating
and troubleshooting experience in pneumatic
conveying and bulk-solids-handling processes. He
holds an M.S. in mechanical engineering from the
University of Wisconsin, Madison - Wisconsin,
and an MBA from Marshall University (Huntington,
West Va.). He has written a large number of
articles and given classes on pneumatic conveying
and bulk solids handling.
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