MULTICRETE
TM
II :
MONOLITHIC CONCRETE
FALSE BOTTOM
UNDERDRAIN .
Underdrains are fundamental to any filter plant. They support the filter media and collect
filtered water. They must also uniformly distribute backwash water, and sometimes air is used
to dislodge contaminants and flush them out of the filter cell during backwashing, returning
the media to a “like new” condition.
One widely used underdrain is a concrete false bottom filter design. Earlier designs
employed precast or cast-in-place piers and precast slab which required extensive field
installation time and were often plagued with quality control problems. To curb the quality
control problems and to improve cost effectiveness, the MULTICRETE II underdrain was
introduced in 1985.
KEY FEATURES
• Easy to Install
• Structurally Sound
• Economical
• Corrosion Resistant
• Non-clogging Design
• Minimal Headloss
• Even Distribution
• Open for Inspection
The integral system of piers, pans and
inserts assures the proper location of all
nozzles. PVC pier forms are furnished cut
to length with properly sized and located
notches to interlock the pan forms. The
ABS plastic pan forms have properly
located recesses for accurate placement of
the nozzle inserts.
Special threaded plugs are installed in
the nozzle inserts prior to shipment to
protect the threads and nozzle seating area
until nozzle installation, and to allow the
option of hydrostatic pressure testing of
the underdrain.
The rebar system furnished by the
installer is anchored into the filter floor
and walls providing a structurally sound
false bottom underdrain.
The floor and piers are made in one
monolithic concrete pour eliminating the
need to pour a system of pier supports
in addition to the filter cell floor, thus
reducing installation costs.
MULTICRETE II underdrains use the
sturdy time-proven ABS plastic nozzles
which are available with horizontal slot
openings sized for the required media. The
large open area of the nozzles minimizes
headloss and the inwardly opening V-shaped
slots prevents plugging. These nozzles are
assembled with stainless steel or ABS screws
and can be disassembled for cleaning.
Shipping costs are minimized because
the bulk of the materials, concrete and
rebar, are acquired locally. Risk of damage
during shipment is low because of the
strong plastic components.
Because of the open plenum design,
this underdrain has minimal headloss,
provides even backwash distribution and
allows inspection access to the area below
the underdrain.
INSTALLATION
Nozzle Assembly
Concrete
Reinforcement Bars
Plastic Inserts
Underdrain Pans
The MULTICRETE II underdrain is
designed for placement with a smooth
level base floor and perimeter support.
While it is easy and economical to install,
it does require that the construction be
performed correctly. Detailed drawings
and instructions are included with the
equipment and must be followed closely
to insure satisfactory results.
Reinforcement Bars
Pier Forms
Holes are drilled into the filter floor
and side walls to accept epoxy grouted
rebars. Following installation of the
vertical rebar, it is good practice to
randomly test for adequate pull
strength. Prior to installation of the
pier and pan forms, the filter floor and
adjacent piping are thoroughly vacuum
cleaned.
APPLICATIONS
The nozzle inserts are attached to
the pan forms prior to or after
installation, depending upon the
installing contractor’s preference.
The pier forms are placed over the
vertical rebar, and the pan forms
are interlocked on top and checked
for level. The rebar is placed and
tied according to the installation
instructions. Care is taken to
prevent debris from entering the
plenum area during installation.
MULTICRETE II is field installed
using a concrete form system consisting of
PVC pier forms, two foot square ABS pan
forms and ABS nozzle inserts furnished by
us. The installing contractor furnishes
adhesive for attaching inserts to the pan
forms, rebar and concrete. In many applications, a primary air distribution header
and water flow baffles are installed before
placement of the form system.
Prior to concrete placement, one of our
field service technicians will inspect the
underdrain installation for proper
placement and cleaning. The contractor is instructed on proper placement,
vibration and finishing techniques for
the concrete by our technician prior to
the first cell being poured. Since it is a
monolithic underdrain, concrete for the
entire underdrain (piers and floor) is
all poured at one time.
MULTICRETE II underdrain systems are
used in concrete and steel filters of any
capacity. In addition to new construction,
they have been used to replace a variety of
underdrain designs in numerous existing
filter plants.
For gravel support filter beds, large
opening flow distribution nozzles can be
used for water only backwash. However,
MULTICRETE II is uniquely suited for
use with media retaining nozzles which
After the slab and pier system
has properly cured, it is
possible to hydrostatically
pressure test the underdrain to
demonstrate the proper
strength under actual operating conditions. After testing
(if included) the insert protector plugs are unscrewed and
the underdrain nozzles are
firmly screwed into place. The
filter cell is now ready for
installation of the filter media.
eliminate the need for gravel support layers. The media retaining nozzles provide
for effective distribution of auxiliary air
scour or combined air and water backwash systems when desired.
MULTICRETE II has been used
extensively with the MULTIWASH
Filtration Process which features the stateof-the-art sustained, simultaneous air and
water backwash method which provides
guaranteed filter media cleanliness
without media loss.
O T H E R WA T E R T R E A T M E N T P R O D U C T S
If it’s in the water, our engineered processes and equipment can take it out, economically
and dependably. Our comprehensive line includes solutions to simple and complex water
treatment and conditioning needs, all backed by working installations and years of experience.
Our line includes:
■ Adsorption Clarifiers®
■ Actifloc™ pre-engineered water plant
■ CONTRAFLO® solids contact clarifiers
■ MULTIWASH® Filtration Process
■ SPIRACONE® sludge blanket clarifiers
■ Gravity filtration equipment
■ Sludge Sucker™ sludge removal system
■ MULTICRETE™ II monolithic under-
drain system
■ Sludge thickeners
■ Vertical and horizontal pressure filters
■ Aerators
■ AERALATER® packaged treatment
■ SCUBA™ block underdrain system
■ ESSD™ filter washtroughs and launder
systems
■ Memcor® CMF
■ Microfloc® Trident® packaged water
treatment
To find out more about how to put
USFilter to work for you,
contact us at
Vertical Pressure Filters
Steel Gravity Filter
Memcor, Microfloc, and
General Filter Products
600 Arrasmith Trail
Ames, IA 50010
515.232.4121 phone
515.232.2571 fax
441 Main Street
P.O. Box 36
Sturbridge, MA 01566
508.347.7344 phone
508.347.7049 fax
CenTROL® Filtration System
Microfloc® Trident ® system
USFilter products and processes for water and
wastewater treatment are protected by patents
issued and pending in the United States and other
countries.
1104 Kenilworth Drive
Fifth Floor
Towson, MD 21204
410.307.6540 phone
410.307.6542 fax
For more information,
visit our web site at
www.usfilter.com
© 2000 USFilter
GF-MC-BR-0600