Dynamic Retarded Spout (DRS) is a patent pending grain flow retarder
developed by Trimill Industrial Systems Inc. DRS effectively and gradually slows down the grain flow in gravity spouts and
keeps the flow velocity low throughout the spout. This eliminates the problems
caused by fast flowing grain in the gravity spouts.
Problems caused by fast flowing grain
Spout and elbow wear - some high throughput spout sections
may have to be
replaced in as few as 3 months. Spout maintenance & replacement is expensive because it requires cranes, labor, materials, and
Downstream equipment wear
(breakage) of friable products, such as corn, pulses and pellets
Creation of fines and dust
Gravity spouting in a grain elevator (left) and in a feed mill
(center & right)
Grain velocity in gravity spouts
Grain quickly accelerates down the spout due to gravity.
Table below shows the grain flow velocity in meters per second in a spout without retarders, as a function of spout
inclination angle and spout length (in meters).
The cells in the table above are color coded
Grain flow velocity up to 6 m/s causes little or no
Grain flow velocity between 6 and 9 m/s causes
Grain flow velocity above 9 m/s causes significant
Current solutions for the high grain velocity problems
Spout liners: AR plate, polyurethane, ceramic tiles
Inline flow retarders
Adjustable spout ends and cushion boxes
Inline flow retarder (left) and
adjustable spout end (right)
Issues with current solutions
Lined spout typically cost significantly more than unlined
Spout liners do not reduce grain or pellet breakage
and creation of fines.
Flow retarders, adjustable spout ends and
cost much more than the spouting of equivalent length.
Bulky - in order to maintain
grain flow capacity, flow retarders require a larger cross section than
the spout, typically around 2.5 times that of the spout.
Limited abrasion reduction.
boxes, while good at reducing abrasion wear in the downstream equipment,
have no effect on the wear of the upstream spouting.
Minimal reduction in grain breakage
and fines generation, because they allow high velocity grain-on-grain
Can get clogged when handling dirty grain
containing large pieces of foreign material, causing production
stoppages due to plugged spouts.
Require access platforms for inspection, cleaning and maintenance.
New Solution: Dynamic Retarder Spout (DRS)
DRS is a patent pending type of flow
retarder developed by Trimill.
DRS uses a series of baffle sets placed at
regular intervals along the length of the spout.
DRS has no choke points and doesn’t create
a stationary pile of material.
DRS typically limits the
grain flow velocity to 4 to 6 m/s.
DRS keeps the grain in motion at all
DRS baffles fit within the
existing cross section of the spout without
reducing the grain flow capacity.
DRS baffles are easy to
install in-situ in the existing spouts.
A DRS baffle set consisting of
a leading (bottom) baffle and a trailing (top) baffle
How does a DRS baffle set work?
DRS baffle set usually consists of two
opposing baffles, one at the bottom and one at the top of the spout, in
a staggered close-coupled arrangement.
A baffle set slows down the grain flow
in 4 steps, by changing the flow direction 4 times. This is done without creating
a slow-moving grain pile, and with a minimum grain-on-grain impact.
At each change of flow direction, the grain
flow is slowed down. Typically, a baffle set reduces the grain flow
velocity by 50% to 70% (the outgoing velocity is 0.3 to 0.5 times the
4 stages of grain flow slowdown by a DRS baffle set
How does a DRS spout with multiple
baffle sets work?
Baffle sets described above are placed at regular
intervals along the spout, causing the grain flow to accelerate and
decelerate multiple times.
The spacing of the baffle set is
determined so that the grain flow velocity never accelerates past the design
velocity of 4 to 6 m/s (smaller spouts allow for a lower design
By keeping the grain flow velocity low, the
grain impact on the baffles and
the spout walls in places, as well as grain-on-grain impact, where the flow changes direction happen at a low grain
flow velocity, causing minimal wear and material breakage.
DRS spout showing grain flow pattern and minimum and maximum grain flow
What are the advantages of DRS over the current
Virtually no maintenance is required
Greatly extended service life of spouts
Reduced breakage of friable bulk material
and fines creation
Work for wide range of grain flows, from
trickle flow to maximum flow
Self-cleaning and resistant to plugging with foreign matter
Fit within the existing
spout cross sections without reducing the capacity
Can be retrofitted to the existing
spouts without changing the spout geometry or configuration
Work in both round and rectangular spouts
Work in both inclined and vertical spouts
Have a lower capital cost than current solutions
Have a lower maintenance costs than current solutions.
Engineering the Dynamic Retarder Spout
Trimill has developed proprietary Grain Flow Simulator app to:
Design the optimum DRS baffle arrangement
for any spout geometry
Predict the grain flow velocity distribution
along the spout, with and without the DRS baffles
Estimate the wear distribution along the spout, with and without the DRS baffles
Create CAD installation drawings for the DRS
Example output from the Grain Flow Simulator of a 5 meter long 12” round spout at 45°
inclination, without and with DRS
baffles. The grain flow velocity is color coded.
Bulk material is wheat and the grain flow is 10,000 cfh (218 t/h)