This spec was used recently for a project. It describes a step screen. Speaking of stepping, check out these boots:
MECHANICALLY CLEANED FINE SCREENS
PART 1 GENERAL
1.01 WORK OF THIS SECTION
A. The Work of this Section includes providing all labor, material, equipment, equipment supports,
coordination, documentation, instrumentation and controls, factory and field testing, and training of
Owner personnel for a complete and operational mechanically cleaned fine screen system.
1.02 REFERENCES
A. The following is a list of standards which may be referenced in this Section:
1. American Bearing Manufacturers’ Association (ABMA): 11, Load Ratings and Fatigue Life for Roller
Bearings.
2. American Gear Manufacturers Association (AGMA):
a. 2015-1-A01, Accuracy Classification System – Tangential Measurements for Cylindrical Gears.
b. 6034-B92, Practice for Enclosed Cylindrical Wormgear Speed Reducers and Gearmotors.
c. 9005-E02, Industrial Gear Lubrication.
3. American Welding Society (AWS):
a. D1.1/D1.1M, Structural Welding Code – Steel.
b. QC 1, Standard for AWS Certification of Welding Inspectors.
4. Anti Friction Bearing Manufacturers Association (AFBMA):
a. Standard 9-90, Load Ratings and Fatigue Life for Ball Bearings.
b. Standard 11-90, Load Ratings and Fatigue Life for Roller Bearings.
5. ASTM International (ASTM):
a. A322, Standard Specification for Steel Bars, Alloy, Standard Grades.
b. A380, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts,
Equipment, and Systems.
c. A480/A480M, General Requirements for Flat-Rolled Stainless and Heat-Resisting Steelplate,
Sheet, and Strip.
d. A507-10, Standard Specification for Drawing Alloy Steel, Sheet and Strip, Hot-Rolled and
Cold-Rolled.
e. C582, Standard Specification for Contact-Molded Reinforced Thermosetting Plastic (RTP)
Laminates for Corrosion-Resistant Equipment.
f. D3917, Standard Specification for Dimensional Tolerance of Thermosetting Glass-Reinforced
Plastics Pultruded Shapes.
6. National Electrical Code (NEC).
7. National Electrical Manufacturers’ Association (NEMA): MG 1, Motors and Generators.
8. National Fire Protection Association (NFPA): 820, Standard for Fire Protection in Wastewater
Treatment and Collection Facilities.
9. Underwriters Laboratory (UL): 674, Electric Motors and Generators for Use in Division 1 Hazardous
(Classified) Locations.
1.03 SUBMITTALS
A. Provide action and informational submittals in accordance with Section XXXXX, Submittal
Procedures, and as identified herein.
B. Action Submittals:
1. Shop Drawings:
a. Manufacturer’s catalog information, descriptive literature, specifications, equipment weight, lifting
points, and identification of materials for construction.
b. Detailed structural, mechanical, and electrical drawings showing equipment fabrications and
interface with other items.
c. Dimensions, size, and locations of connections to other work.
d. Details of attachment and support.
e. Gear output torque and rake weight lifting capacity calculations.
f. Complete motor nameplate data, as defined by NEMA, motor manufacturer, and motor
modifications. See Section XXXXX, Low-Voltage AC Induction Motors, for motor submittal
requirements.
g. Control Panel elevation drawings showing construction and placement of operator interface
devices and other elements.
h. Power and control wiring diagrams, including terminals and numbers.
i. See Section 40 99 90, Package Control Systems, for additional submittal requirements.
j. Shop painting systems, including manufacturer’s descriptive technical catalog literature and
specifications.
k. External utility requirements for air, water, power, drain, etc., for each component, including
pressure and flow rate.
l. Drawings of equipment enclosures designed and stamped by professional structural engineer.
m. Anchorage and bracing data sheets and drawings as required by Section XXXXX, Anchorage
and Bracing.
C. Informational Submittals:
1. Statement of Qualification: Professional structural engineer.
2. Manufacturer’s Certificate of Compliance of factory-applied coating system.
3. Manufacturer’s installation instructions.
4. Special shipping, storage and protection, and handling instructions.
5. Written factory test report of inspection.
6. Manufacturer’s Certificate of Proper Installation in accordance with Section XXXX, Manufacturers’
Field Services.
7. Field functional test reports.
8. Manufacturer’s warranty.
9. Operation and Maintenance Data: As specified in Section XXXX, Operation and Maintenance
Data, including routine maintenance requirements prior to plant startup.
10. Welder/welding operator qualifications.
11. Welding inspector credentials.
12. Welding Inspector’s Report.
1.04 QUALIFICATIONS
A. Registered Professional Structural Engineer.
B. Welder/Welding Operator: In accordance with AWS D1.1/D1.1M.
C. Welding Inspector: Certified in accordance with AWS QC 1, and having prior experience with welding
codes specified.
1.05 EXTRA MATERIALS
A. Provide recommended list of spare parts in the Operations and Maintenance Manual, in accordance
with Section XXXXXX, Operation and Maintenance Data.
B. Provide one set of special tools required to maintain or dismantle equipment.
C. Delivery: In accordance with Section XXXXX, Common Product Requirements.
PART 2 PRODUCTS
2.01 GENERAL
A. Each piece of equipment specified shall be designed for continuous operation, 24 hours per day, 7
days per week.
B. Each piece of equipment specified shall be fabricated from Type 316L stainless steel having a bead
blasted finish unless noted otherwise.
C. Painting and coatings shall comply with Section XXXXX, Painting and Coating for Equipment
Prepurchase.
2.02 MANUFACTURERS
A. The design of the process for screening materials from raw sewage is based on the equipment from the
first named manufacturer herein listed and as shown on the Contract Drawings.
B. Materials, equipment, and accessories specified in this Section shall be products of:
1. Huber Technology Inc., Model SSF-HF.
2. Vulcan Industries.
3. Johnson Screens.
2.03 SYSTEM DESCRIPTION
A. This Section specifies mechanically cleaned stair type screens for collection and removal of solids and
fibrous material from municipal wastewater.
B. Manufacturer shall provide screens, motors, gear reducers, solenoid valves to control wash water flow,
level elements and transmitters, controls, control panels, and lifting attachments, as a complete
integrated package to ensure proper coordination, compatibility, and operation of the system.
C. Mechanically Cleaned Screen
1. Each mechanically cleaned screen shall be a stair type screen with two sets of vertical plates, one
movable and one fixed. Each mechanically cleaned screen shall consist of a frame, gear reducer,
motor, mounting legs, fixed pivot point for lifting screens from channel, and all necessary
appurtenances to provide a complete mechanical screening system.
2. The screen shall be cleaned by the rotating motion of a movable set of step-shaped vertical
plates. As the plates rotate, they shall lift trapped waste materials to the next stair of a fixed set of
vertical plates. The moving action shall not result in an appreciable quantity of screened
material falling or rolling off of the screen back into the influent wastewater.
3. At the top stair of each screen, the waste materials shall discharge into a discharge chute without
the use of brushes or spray washers. The discharge chute shall direct the screenings into a sluice
trough (provided by others).
4. The screen assembly shall be designed with a pivot and lifting arrangement that will allow the
screen to be rotated out of the channel for maintenance access. No disassembly or any other
operation shall be required when lifting the screen. All other screens and the sluice trough
(provided by others) must remain operational while an individual screen is completely or partially
pivoted out of its channel.
2.04 OPERATING CRITERIA
A. Equipment furnished under this Section shall be suitable for operation in municipal wastewater. The
wastewater will contain fine and fibrous material including but not limited to hair, plant material, sand,
silt, petroleum products, industrial solvents, animal fats, oils and plastic bags.
B. Equipment will be exposed to variable concentrations of hydrogen sulfide.
C. Each screen shall be designed for continuous operation, and shall be suitable for operation under the
following conditions:
1. Number of Units: Two.
2. Exposure: Indoors.
3. Peak Hourly Flow (per screen): 55.2 mgd.
4. Average Daily Flow (per screen): 24 mgd.
5. Minimum Flow (per screen): 2.9 mgd.
6. Wastewater Temperature Range: 40 to 80 degrees F.
7. Wastewater pH Range: 6.3 to 7.5.
8. Channel Width: 5 or 6 feet.
9. Channel Depth: 9.0 feet.
10. Maximum Upstream Water Depth (feet), 40 Percent Binding/55.2 mgd per Screen: 5.5 feet.
11. Minimum Downstream Water Depth at 2.9 mgd/Screen: 1.0 feet.
12. Channel Invert Elevation (at screen): 4967.00.
13. Channel Invert Elevation (upstream of screen): As recommended by manufacturer.
14. Operating Floor Level: 4976.00.
15. Screen Frame Angle from Horizontal: 45.
16. Open Space Between Screening Blades: 6 mm.
17. Screening Plate Width: 3 mm.
18. Minimum Height of Screenings Discharge from Floor: 3 feet 0 inches.
19. Minimum Slope of Sluice Trough: 2 percent.
20. Maximum Height of Screening Handling Equipment: 14 feet.
2.05 MATERIALS
A. Unless otherwise specified herein the equipment shall be manufactured from AISI Type 316L stainless
steel shapes, pipes, and sheets. All mechanical parts shall be designed to handle the forces that may be
exerted on the unit during fabrication, shipping, erection, and proper operation.
B. The equipment, after its fabrication, shall undergo a passivation (pickling) process to ensure maximum
resistance to corrosion. All stainless steel components and structures shall be submersed in a chemical
bath of nitric acid and hydrofluoric acid to remove any residues that may be present on the material as
a result of forming, manufacture, or handling. After removal from the pickling bath, the equipment must
be washed with a high-pressure wash of cold water to remove any remaining surface debris and
promote the formation of an oxidized passive layer, which is critical to the long life of the stainless steel.
Submergence insures complete coverage. Spray on chemical treatments and glass bead blasting are
specifically not acceptable due to their inability to provide complete and uniform corrosion protection.
2.06 FINE SCREEN EQUIPMENT
A. General:
1. Lubrication points for gears and motors shall be located outside of the enclosure when possible and
shall be accessible from the operating floor level. There shall be no parts requiring lubrication located
under water. Oil lubricated gear reducers shall be provided with sight tubes to indicate oil levels.
2. The screen support shall have a fixed pivot mount allowing it to be lifted out of the wastewater to a
horizontal position where it is easily accessible from the operating level. Pivoting the screen shall not
require disassembling the screen, or disassembling or moving the sluice trough.
3. Each screen is to be a totally enclosed structure. Each screen enclosure shall be provided with a 4-inch
stub flange for connection to the odor control system. The stub flange shall not be located on one of
the removable panels.
B. Welding: All welding shall conform to AWS-D1. Weld splatter shall be prevented by the use of
splatter-prevention paste at welded joints. Weld slag shall be removed.
1. After welding operations, stainless steel components shall be cleaned of organic contamination using a
solvent that is free of chlorides. After organic materials have been removed, embedded iron shall be
removed from the stainless steel by pickling with nitric or hydrofluoric acid.
2. Welded ferrous or steel components shall be provided with continuous weld between full penetration
skip welds or sealed with a paintable silicone caulk.
C. Frame of Screen:
1. Frame shall be fabricated from 0.2-inch (5-mm) thick AISI Type 316L stainless steel. The frame shall
accommodate fixed step blade packages, blade cross pieces, slewing bracket unit, eccentrics, and
drive unit including gear, shaft, and motor.
2. Frame shall be accurately set into position in the channel and shall be capable of supporting the entire
screening assembly when suspended from the pivot shaft attached to the support legs. The screen shall
be installed with an angle of 45 degrees from the horizontal. If the total screen width is less than the
specified channel width, the opening shall be sealed to prevent flow from passing around the screen.
3. Frame sides shall be fully welded to a 0.2-inch (5-mm) thick baseplate, stationary 0.16-inch (4-mm)
thick step blade cross member brackets and a 0.2-inch (5-mm) thick drive console. The drive console
shall be designed to accommodate eight adjusting bolts. Four adjustment bolts shall be parallel to the
screen angle and four shall be perpendicular to the screen angle. The parallel bolts shall adjust the
horizontal position of the moveable step blades. The perpendicular bolts shall adjust the vertical
position of the moveable step blades.
4. The frame sides shall form the supports for cover panels at the sides, the front, and the back of the
screen.
D. Step Screen Blades:
1. Moveable step blades shall be cut from 1/12-inch (2-mm) thick cold- rolled stainless steel sheets. The
front-face of the step blade shall have a curved, hook-like shape thus preventing screenings from
rolling or falling down from the steps. The steps shall have a horizontal length of 2 inch (50 mm) and a
vertical height of 4-1/8 inches (105 mm) from step to step. The rear-face of the moveable step blade
shall have a series of saw-tooth patterns cut into the straight edge of the step blade to slice through any
debris that may accumulate on the cross member supports for the stationary step blades. Each saw-
tooth pattern shall consist of ten angular cuts in succession, resulting in a 7-7/8-inch (200-mm) long
serrated edge along the rear-face of the step blade. Each cut shall consist of a 13/16-inch (20-mm)
straight length angled 14 degrees off the rear step blade straight edge followed by a 1/5-inch (5-mm)
cut perpendicular to the straight edge. The moveable step blades shall be mounted in a series of cross
member brackets anchored to the moveable side plate.
2. Stationary step blades shall be manufactured from 1/12-inch (2-mm) thick cold-rolled stainless steel
sheets. The stationary step blades shall have exactly the same step shape as those of the moveable step
blades. The stationary step blades shall be mounted in a series of cross member brackets anchored to
the step screen frame.
3. The effective screening area of the step screen shall be produced by alternating stationary step blades
with moveable step blades and spacing the step blades 1/4-inch (6-mm) apart. The open space
between the lamina is maintained by 3-inch long HDPE spacer inserts mounted along the length of the
moveable step blades at a distance not less than 2 feet apart. The resulting effective screening area
shall have a minimum of 75 percent free open-area.
4. The movable step blades lift the screenings to the next higher stationary step with each rotation cycle of
the gear motor. The number of rotation cycles performed in each operating cycle is dependent upon
the hydraulic conditions in the channel. After completion of an operating cycle, the step blades shall
come to rest in the home position such that the horizontal surface of the step blades are aligned across
the width of the channel. A proximity sensor shall send a signal to the PLC when the moveable step
blades are in their home position causing the gear motor to stop and hold the step blades in alignment.
5. The screen shall utilize two sets of step blades consisting of upper and lower packages. The upper
blade package shall consist of 2-mm thick moveable stainless steel blades and 6-mm thick fixed
polypropylene blades to prevent debris falling into the channel prior to discharge unless all stainless
steel upper lamina are required. The resulting tolerance between the plastic jacket and the adjacent
stationary step blade shall be 0.04 inch (1 mm).
E. Bottom Flushing Pipe: A 1-1/4-inch diameter stainless steel flushing pipe shall be mounted parallel to
the back of the faceplate along the width of the channel to prevent heavy material from depositing
below the step blades. The flushing pipe shall have 1/2-inch diameter perforations every 8 inches. The
flushing pipe will be fed with nonpotable plant effluent through a stainless steel pipe. The flushing pipe
shall be fitted with a solenoid valve controlling the feedwater to the flushing pipe. Solenoid valve must
meet Class I, Division 2 requirements. Screens with effective screening areas greater than 4 feet 4
inches shall be equipped with dual flushing pipes and dual feedwater connections.
F. Home Position Sensor:
1. Home-position proximity sensor shall send a signal to the plant control system that shall cause the gear
motor to stop the rotation of the moveable step blade package, when it is aligned with the stationary
step blade package. The signal shall be generated when the metal flag attached to the eccentrically
rotated block passes the frame mounted sensor.
2. Mounting mechanism of the sensor shall be adjustable to enable the moveable step screen package to
be stopped in the proper location.
3. The proximity sensor shall be an inductive proximity sensor. The sensing distance of this sensor shall be
5/64 inch (2 mm).
G. Gear Motor Drive Mechanism:
1. The drive unit shall be a gear motor rated for continuous duty and shall be selected to match the
requirements of the particular screen. The drive motor shall be a 5-horsepower unit designed for
application in a Class I, Division 2 area. The motor shall be a constant speed unit rotating at
1,680 rpm, and shall be powered by 230/460V ac, 60-Hz, three-phase power. The motor shall be
compatible with an adjustable drive system to be supplied by others. Provide motors in accordance
with Section XXXX, Low-Voltage AC Induction Motors, and Induction Motor Data Sheet located
in Supplements following End of Section.
2. The drive unit shall be direct coupled to the screen drive shaft through the gear box. The gear box
housing shall be constructed from ASTM A48, Class 30 cast iron. The drive unit shall be sealed from
the screenings transport area with a stainless steelplate, which is welded to the frame and forms the
drive console.
3. The screen shall be equipped with electronic overload protection by one true-power monitors to stop
the screen and initiate an alarm in the event of overload. The true-power monitor shall monitor both the
upstroke and the down-stroke of the screen. Shear pins for overload protection are not acceptable.
H. Covers:
1. The step screen shall include AISI Type 316L stainless steel covers for odor control and general plant
safety. The covers shall extend from the deck level to the top of the screen. The covers on the front of
the screen shall be easily removable. The covers on the sides and the back of the screen shall be
fastened in place by screws.
2. Each screen cover shall be provided with a 4-inch stub flange for connection to the odor control
system. The stub flange shall not be located on one of the removable panels.
2.07 ELECTRICAL
A. General:
1. All electrical components and assemblies shall bear a UL 913 label. All electrical work shall conform
to the requirements of this and other referenced sections of these Specifications.
2. All electrical components at the screen or within the screen housing shall be rated for Class I, Division
2, Group D Hazardous Environment as defined by the NEC.
2.08 ADJUSTABLE FREQUENCY DRIVE
A. Each screen motor shall be compatible for use with a UL certified AFD (Adjustable Frequency Drive).
AFDs shall be provided by others.
B. The AFD shall operate at half speed for normal operation of the screen and full speed during high
screening loading conditions.
2.09 INSTRUMENTATION AND CONTROLS
1. In accordance with general control requirements specified in Section 40 99 90, Package Control
Systems.
2. Each Fine Screen shall be supplied with local control panel, as defined below:
Fine Screen 1 Local Control Panel:
310LCS35001
NEMA 4X
316 Stainless steel
Fine Screen 2 Local Control Panel:
310LCS35002
NEMA 4X
316 Stainless steel
3. Each Local Control Panel shall be provided with the following:
a. Fine Screen LOCAL/REMOTE selector switch
b. Fine Screen EMERGENCY STOP pushbutton
4. Fine Screen System remote control and alarm monitoring provided by plant control system, furnished
by others.
5. UL Listing Mark for Enclosures: Mark station “Listed Enclosed Industrial Control Panel” per UL
508A.
2.10 FINISHES
A. For nonstainless steel and nonaluminum metal surfaces, prepare, and prime, and finish cost in
accordance with Section XXXXXX, Painting and Coating for Equipment Prepurchase.
B. Stainless steel shall be cleaned and passivated following fabrication in accordance with ASTM A380.
2.11 SOURCE QUALITY CONTROL
A. Factory Tests and Adjustments:
1. The screens shall be factory assembled and factory tested at the point of manufacture. Test each screen assembly, in its operating position, to ensure proper operation of plates, controls, protective devices, and override controls.
2. Run equipment and test for minimum 6 hours. Testing shall be done in factory with unit oriented in its installed position.
PART 3 EXECUTION
3.01 PRODUCT DELIVERY, STORAGE, AND HANDLING
A. As specified in Section XXXXX, Common Product Requirements.
3.02 INSTALLATION
A. In accordance with manufacturer’s written instructions.
B. Anchor Bolts: Accurately place using templates provided by manufacturer, and as specified in Section
XXXXX, Metal Fabrications.
3.03 FIELD FINISHING
A. Touchup damaged areas of painted ferrous metal in accordance with and as specified in Section
XXXX, Painting and Coating for Equipment Prepurchase.
3.04 FIELD QUALITY CONTROL
A. Perform in accordance with Section Engineer, Equipment Testing and Facility Startup.
B. Functional Test:
1. Conduct on each unit with potable water (or other suitable water).
2. Test shall include 6 hours of continuous operation of each piece of equipment specified herein.
3. Confirm coordination of operation with sluice trough, diverter gates, and washer/compactors.
4. Head Loss at Operating Condition: The Subcontractor shall demonstrate a head loss less than the
maximum while passing the design flow.
5. Any noticeable damage to the equipment shall be considered a failure.
6. Supply required metering devices and gauges necessary to demonstrate system performance. Supply
and install gauge connections as required.
C. Performance Test:
1. Conduct on each unit.
2. Test system during process commissioning with specified service fluid.
3. Test shall include 6 hours continuous operation of each piece of equipment specified herein.
4. Successful functional tests done with water shall not constitute acceptance of screening system. System
will only be accepted after successful performance tests on specified fluid at stated Operating Criteria.
5. The step screen shall operate automatically based on the water level differential.
6. Proposed test procedures shall be developed by the Manufacturer and submitted to Engineer for
review, comment and approval. Testing shall not begin until the test procedures have been approved
by Engineer.
7. A qualified representative of the manufacturer shall supervise each test, analyze data, and certify the
equipment’s performance during the test.
8. In the event that the equipment does not meet the requirements of the specifications during the
performance test, the representative of the manufacturer shall make such changes in the equipment and
methods of operation as deemed necessary and as approved by Engineer and pay for all reasonable
costs to re-test, including those of Engineer and Owner. The necessary adjustments shall be made as
soon as practical, but within a period not to exceed 30 days. Following the adjustments, make a
second test regime similar to the first testing regime. In the event that the equipment still does not
achieve specified performance during the second test, then the equipment will be subject to rejection.
9. If, after a maximum of two test runs, in the opinion of EngineerL, the equipment meets the performance
requirements specified herein, Engineer will recommend the acceptance of the equipment. If, in the
opinion of Engineer, the performance test results do not meet the requirements specified herein,
Engineer will notify the manufacturer and the Owner of the non acceptable performance Any failure of
the performance requirements shall be deemed defective Work under the Purchase Order executed
between Engineer and Manufacturer.
3.05 MANUFACTURER’S SERVICES
A. Manufacturer’s Representative: Present at Site or classroom designated by Owner, for minimum
person-days listed below, travel time excluded:
1. One trip for 3 person-days for installation assistance and inspection.
2. One trip for 3 person-days for functional testing, completion of Manufacturer’s Certificate of Proper
Installation, and training. Training shall not commence until an accepted detailed lesson plan for each
training activity has been reviewed by Owner and Engineer.
3. One trip for 3 person-days for facility startup.
4. A credit shall be applied to Engineer for any unused manufacturer Field Services.
B. See Section XXXX3, Manufacturers’ Field Services, and Section XXXXX, Equipment Testing and
Facility Startup.
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