General Construction Specifications
PART 1 - GENERAL
01 DESCRIPTION OF WORK
A. The Contractor shall furnish and install screening (bar screens, screenings hopper, grinders, and etc.) as specified herein and shown on the Contract Drawings. The shall be installed in phases as described in the Contract Documents.
B. The Contractor shall furnish and install all required accessories for a complete and operating screening system.
C. The Contractor shall be responsible for coordinating the interfacing of the various items as required for a complete and operating screening system.
02 REFERENCES
A. The screening described in this specification shall be manufactured with new components of the highest quality available. The following codes and standards shall apply wherever applicable.
1. NEMA - National Electrical Manufacturers Association.
2. ASTM - American Society for Testing and Materials.
3. AGMA - American Gear Manufacturers Association.
4. ANSI - American National Standards Institute.
5. ASTM A536-77 - Standard Specifications for Ductile Iron
Castings.
6. 4130 - Heat Treated Alloy Steel.
7. 43-48 - Rockwell C.
1.02 PERFORMANCE
A. The screening shall remove debris from the sewerage flow, elevate and dump the debris into the screenings hopper where the grinder will grind the debris and dump the remains into the sewerage flow.
B. The Contractor shall make certain that the does not exceed the space allocation and provide the manufacturer with Contract Drawings where necessary.
PART 2 - PRODUCTS
03 BAR SCREENS
A. The front-cleaned screen shall be designed of rugged construction to withstand the forces exerted by the liquid and the material to be screened. The framework and functional parts shall be designed to provide maximum efficiency and long life. The shall consist essentially of a front cleaned screen, an automatic rake mechanism, a drive system, frame and dead plate, all construction of 304 SS and shall be factory assembled and tested prior to final delivery. The local controls shall be supplied by the manufacturer of the screen.
B. There shall be furnished and installed by the Contractor (4) four front-cleaned bar screen(s) set at an angle of 80° from the horizontal. In general, the to be supplied must conform to the specifications detailed herein. For all acceptable screens, the maintenance on the drive system shall be performed at a level above that of the operating floor.
C. The units supplied shall be as manufactured by Vulcan Industries, Inc. or an approved equal.
D. Operating Conditions:
1. Maximum Flow: 140 MGD with 3 screens operating
2. Screening Size: 1"
3. Channel Depth: 39'-0" ±
4. Channel Width: 2 at 6'-0 and 2 at 8'-0"
5. Quantity: 4
B. The bar rack shall consist of a sufficient number equally spaced parallel steel bars with 1" clear spacing between each. The removable bar screen shall extend from a bolted bottom plate to a bolted connection angle for easy removal. The bars shall be welded in place to assure complete rigidity. The parallel bars shall be 3/8" wide by 2-1/2" deep by 10'-0" long and shall be constructed of 304 SS.
C. A 304 SS dead plate shall extend from the bar connection angle to a sufficient discharge level. It shall be true and flat so that the rake teeth will ride no closer than 1/16" and no higher than 1/4". It shall be securely fastened to the chassis of the unit. The dead plate shall be 1/4" thick.
D. A spring-loaded traveling rake shall be provided to remove the collected materials on the bar screen. The rake head shall have rake teeth sized to fit between bars of the screen and will be able to travel and the length of the screen without binding or jamming. The rake arms, constructed of 304 SS, shall be manufactured to the following dimensions: 3" square with 7 ga wall by 12'-0" long. The rake head shall be 3/8" thick by 10" deep and shall also be constructed of 304 stainless steel.
E. The rake shall be attached to the two driven roller chains with hardened steel bolts. The rake arm shall ride on a roller in a single guide channel on each side of the chassis.
F. It shall be arranged in such a manner that the rake will be lifted on the down cycle and allowed to clear the bar screen. When the rake reaches the end of its downward travel direction, it will be rotated into the bar screen to remove the collected debris. The springloaded rake shall be designed to pass over lodged or excessively large objects as it enters the bars on its upward travel and return to its original position to continue the raking cycle.
G. The rake arm mechanism shall have a constant up and down traveling speed of 20' per/min.
H. The dual roller chains shall be #120 and shall have correspondingly sized sprockets with grease lubricated bearings. The sprockets shall be of the same material as the chain. Grease lines shall extend from each grease lubricated sprocket to the operating level of the bar screen.
I. The rake shall be designed to reach the discharge elevation set above the floor level and clear past the dead plate as the guide rollers follow the guide channel's change in direction. The rake then engages a pivoting wiper mechanism consisting of a replaceable polyethylene wear plate and 304 SS framework. The wiper follows the rake head surface as the rake head continues its upward travel, pushing the screenings off the entire rake surface and into the screenings hopper.
The rake shall travel around the drive sprockets, pivot on the rake guide rollers to raise the rake head above the dead plate and to begin the downward movement.
J. The debris shall be discharged from the rake onto a 10 ga 304 SS metal sheeting chute mounted at an angle as required to discharge into the screenings hopper.
K. The frame shall be made of 3/8" 304 SS plate. The frame shall be assembled by using plate formed to make a rigid channel framework which when properly anchored in accordance to the manufacturer's instructions, will withstand all the forces encountered by the installation.
L. The drive assembly shall be complete with an adjustable mounting frame, motor, 1 gear reducer and V-belt drive. The motor shall be an explosion proof, 2.0-HP, 1.15 S.F., class F insulation, 230/460 volts, 3 phase, 60 cycle current. The gear reducer shall be of sufficient size to lift twice the weight of the rake and its debris load. The gear shall have a service factor of 1.25. The motor and gear reducer shall be designed for installation outdoors (Class I, Div. I).
M. All shafting shall be made with 304 SS and shall conform to ASTM specification A-276.
N. The gear reducer and motor assembly shall be mounted on an adjustable 304 SS platform in such a manner that when an overtorque condition is transmitted to the gear head a torque limiter, attached to the gear reducer input shaft, shall disengage at a pre-set torque value, disconnecting the drive enertia from the unit. The disengaging torque limiter shall at the same time make contact with a limit switch that will drop out the control system, thus stopping movement of the raking mechanism. The torque device shall reset automatically when the overtorque condition has been eliminated.
O. A safety guard, conforming to OSHA standards, will be provided for the V-belt drive assembly. All guards shall be 304 SS.
P. The control panel shall be supplied by the manufacturer. It shall be totally automatic and provide all protection to prevent damage to the bar screen.
Q. Control:
1. Basic control (locally mounted)
a) A (Class I, Div. I) limit switch to stop the drive in the event of
an overtorque condition.
b) A (Class I, Div. I) limit switch to stop the rake assembly at the end of the cleaning cycle in its upper-most position.
c) A (Class I, Div. I) drum controller/selector switch, 3-position, forward-off-reverse (momentary) to control the basic functions of the bar screen.
2. The control panel shall be totally pre-wired and shop tested before shipment. It shall include all appurtenances necessary for automatic operation of the bar screen and also the protection of the electrical components.
a. The control panel shall include, but not limited to the following components.
1. Enclosure (Class I, Div. I)
2. Circuit Breaker.
3. Reversing Magnetic Starter.
4. Control Transformer.
5. Control Relays.
6. Selector Switch (s) (Hand-Off-Auto, Forward-Off- Reverse).
7. Push Button(s) (Over Load Reset, High Water Reset, Overtorque Reset).
8. Indicating Pilot lights (Power ON, Over-Load, Alarm, Forward, Reverse, High Water, Auto).
9. Terminal Strip.
10. Programmable time clock.
11. Differential Pressure Detection System.
12. Cycle Totalizer.
3. The bar screen shall operate under the following automatic modes:
a) Differential Pressure: When the differential pressure across the bar rack reaches a preset (field adjustable inside control panel) level the bar screen shall cycle.
b) Timed Cycle: When the present (field adjustable inside control panel) timer reaches its set point the bar screen shall cycle.
4. The grinder shall start when the bar screen starts its cycle. It shall continue to run until the bar screen stops and a preset (field adjustable inside control panel) timer times-out.
5. The control panel shall be wired from remote status indication and operation from the main control panel and the telemetry system.
R. Spare Parts
1. The supplied spare parts for each bar screen:
a) One polypropylene wiper blade.
b) One limit switch without arm.
c) Two rake connecting inserts and bolts.
d) Four rake roller bearings.
e) Four idler sprocket bearings.
S. All painting shall be as required in Section 9900. All shall receive a two coat epoxy coating on a primed surface.
2.02 GRINDERS
A. The grinder shall be of the two shaft design. One shaft shall turn at 2/3 the speed of the other shaft. Shafts shall be constructed from 4140 steel hexagon stock. The two shafts shall counter rotate and be equipped with spacers and intermeshing cutters. Cutters and spacers shall be cast from 4130 steel, surface ground for uniformity and thoroughly hardened to 43-48 Rockwell C.
B. Cutters and Spacers: The inside configuration of the cutters and spacers shall be hexagonal so as to fit the shafts with a total clearance not to exceed 0.040 inch across the flats to assure positive drive and increasing the compression strength of the spacers.
C. Cutter Design: The cutter design shall be of the 7-tooth design. To maintain particle size, the height of the tooth shall not exceed 3/4 inch above the root diameter, and shall exert a minimum force of 400 lbs. per HP continuously and 1200 lbs per HP at momentary load peaks at the tooth tip. Cutter root diameter overlap shall not be less than 1/16 inch or greater than 3/8 inch to maintain the best possible cutting efficiency while incurring the least amount of frictional losses.
D. Speed Reducer
1. Planetary type.
2. Grease filled.
3. "Heavy Shock" load classification.
E. Materials:
1. The grinder shall be constructed of corrosion resistant material and must be compatible so as to resist corrosion due to cavitation or galvanic action.
2. End Housing, Transition Flanges, and Covers: Cast of Class 30 grey iron.
3. Side Rails: Cast of ASTM A536-77 ductile iron.
F. The sewerage grinder shall be capable of operating continuously, processing dry debris from bar screens in sewerage.
G. Seals shall be of the mechanical face type and require no external water source.
H. Bearings shall be the sealed oversize conrad type ball bearings.
I. Couplings: The high speed shaft of the grinder and motor shall be directly coupled with each other using two- or three-piece couplings.
J. Motor
1. Explosion proof (Class I, Div. I).
2. 10 HP maximum.
3. 1725 rmp, 60 Hz, 3-phase, 460 volt plus or minus 10%.
4. Efficiency factor not less than 87% at full load.
5. Power factor not less than 82% at full load.
K. Motor Controller: The motor controller shall utilize a solid state logic design. Line transient protection to 1000 volts. A transformer shall supply all low and intermediate control voltage. All transformer legs shall be fuse protected. The controller shall provide thermal motor overload protection and single phase protection.
1. The controller shall provide the following functions:
a) The controller is equipped with a "Local", "Off", "Remote" switch. In the "Off" position, the electrical motor shall not run. In the "Local" position, the panel controls are used. In the "Remote" position, the grinder shall start and run with the bar screens. there shall also be a pump interlock which restricts resetting an overload condition from the remote connection. The unit can only be reset from the local panel controls.
b) Operate in a normal ON/OFF mode.
c) Low voltage, loss of phase, over current protection.
d) Full load protection.
e) Jam or overload protection.
1. Upon the grinder encountering a jam or overload condition, the controller shall stop the grinder and reverse its rotation to clear the obstruction. If the jam is cleared, the controller shall return to normal operation. If the jam condition still exists, the controller shall go through two additional reversing cycles within 30 seconds (3 times total) before signaling a grinder overload condition. Upon a grinder overload condition, the controller shall shut off the grinder and activate an alarm circuit.
f) Motor Controller Hardware
1) U.L. Approved enclosure (Class I, Div. I) explosion proof, 18" x 16" x 8".
2) Indicator lights for Line Active, Overload, and Run conditions.
3) Monetary contact pushbutton switches to perform Start and Stop/Reset operations.
4) Overload terminals shall be provided for remote, overload and/or alarm indication.
L. The grinders shall be furnished with one set of spare cutters each and any special tools required for the maintenance of the grinders.
M. The grinder and other accessories installed with the grinder shall receive a shop coat of rust inhibitive primer and the manufacturer's standard two part epoxy coating on blast cleaned surfaces.
N. The grinder shall be a muffin monster as manufactured by Disposable Waste Systems, Inc., Santa Ana California.
O. Grinder Schedule:
Grinder Location # Required Design Flow Model #
Bar Screening Hopper 4 Dry Debris 40000-0024
04 SCREENINGS HOPPER
A. Each grinder/bar screen shall be supplied with an aluminum screenings hopper as shown on the Contract Drawings.
B. Each screenings hopper shall be sized and designed for removal of the grinder. the grinder shall bolt to the screenings hopper as shown. Screw jacks shall be provided for raising and lowering the grinder.
C. Anchor bolts shall be stainless steel with stainless steel hardware.
D. All parts of the screenings hopper shall be aluminum or stainless steel.
E. All dissimilar metals shall be protected as required.
F. Screenings hopper shall be painted as required under Section 09900 - Painting screening hopper shall receive a two coat epoxy coating on a primed surface.
PART 3 - EXECUTION
05 INSTALLATION
A. Install the as shown on the drawings and in accordance with the manufacturer's recommendations.
B. Obtain the services of the manufacturer's factory service engineer to check the installation of the and make any field adjustments necessary to ensure proper operation. The service engineer shall certify to the Engineer in writing that the has been satisfactorily installed and adjusted for continuous operation.
C. Provide the services of the manufacturer's service engineer for the number of days required in order to instruct plat personnel in the proper operation and maintenance of the system, minimum one (1) day.
END OF SECTION
