The first Filtering screen PEGASUS step screen was installed in Alicante, in October, 1992 in Rodelco, S.A., a private company of the meat sector.
The performance and almost null maintenance results, constituted together with the by- pass channel elimination, a new concept in step screen.
The characteristic that identifies the PEGASUS step screen is the design of the hook and of the transmission-cleaning wheel. This development began in 1989 and during these years it has been improved until it has reached the exact measurements that guarantee the best performance and the maximum life. In the following pages the reasons are explained.
It has a 152.4 mm bar spacing. With this measure we guarantee the best performance.
When this measure is increased, deformations of the hook are produced by incrustations of wood or other objects between them. The charge loss increases if we increase the hook’s thickness in order to increase the rigidity.
When this measure is diminished, the charge loss increases, as well as the cost of the equipment, without any considerable advantage.
The dimension of the hook of 32 mm adapts to the maximum elevation measures of wastes (look at the following pages), since with 60º of inclination we can lift wastes of 125 mm of diameter, and with 75º, the most common, of 85 mm of diameter.
To increase this length implies creating deformation problems because of impact, that deteriorate the hooks and that make the discharge to be problematic, and no advantage is achieved.
The 1.5 mm thickness provides a resistance and perfect dimensional stability. If the thickness is diminished, deformations are produced and even vegetable elements could be cut and incrusted between the hooks.
If the thickness increases, we only increase the loss charge without any advantage.
The step screen movement is produced by the rotation of an axis located in the machine’s bolster, which is powered by a hollow axis driver. We can eliminate the transmission chains with this system, as well as the tightening elements and the maintenance it involves
In machines with 6 mm or more bar spacing, the step screen dragging is performed by means of PVC pieces that produce at the same time, the cleaning.
Being dragged in all the length, the PEGASUS step screen can have a width up to 2000 mm without suffering deformations and without having to place two step screens one beside another to cover the space.
In machines of less than 6 mm of bar spacing, dragging is carried out through the same lateral and central sliding wheels.
In both cases the step screen does not need the installation of lateral or central chains. With this we eliminate maintenance, wearing down and un tightening between the lateral chain of a material and the step screen of the other.
The inferior seal with the channel is carried out by support of the machine in the bottom; the closure with the hooks is made through a jagged nylon brush that does not allow the pass of solids.
In very wide machines a set of two brushes are placed.
The loss in the level of water is the lowest in this kind of step screens, 35 mm for 75 º and 31 mm for 60º.
Each self cleaning step screen is formed by filtrating elements of AISI-304 O 316 stainless steel, built in parallel with the separation indicated in the technical data sheet.
The set is built-in a stainless steel AISI-304 o 316 structure, conformed and welded.
The step screen is supported and guided through the support structure, by means of articulated plastic guides highly resistant to wearing down and to impact, UHMWPS type.
All the pieces in contact with water are of AISI-304 or 316 stainless steel, except the guide articulations and separations that are UHMWPS type.
The step screen movement is carried out through a combination of dragging mechanism that has the double purpose of serving as a toothed wheel for movement and as expeller of wastes that remain trapped between filtrating plates (patented system).
The step screen can be turned very easily because it is supported only by a transversal axis, this characteristic allows a simple and out of the water maintenance.
Under this title are included all materials, equipment, manpower and supervision necessary to supply, install and put to work adequately a continuous self cleaning step screen and accessory elements, , such as specified here and indicated in the drawings.
The equipment that is supplied and installed is a self cleaning filtrating step screen, completely automatic, the equipment is of the most advanced design and is manufactured with materials and methods capable of achieving the functions described ahead. The equipment will be installed in the screening channel as indicated in the drawings.
All equipment that appears in this section will be supplied by or through an only manufacturer who will be responsible for the design, the coordination and correct operation of the whole system. It will be manufactured, built- in and placed in adequate operation conditions agreeable with the drawings, specifications, technical data, instructions and recommendations of the equipment’s manufacturer except for cases determined by the engineer.
The unit will be supplied and installed completely with all the bolsters in stainless steel, all the necessary mechanical equipment for the adequate operation, including the complete powering units, as indicated in the drawings, and all as indicated in the drawings, and all material or additional construction that those specifications need and the manufacturer’s design.
The filtrating high resistance step screen, completely automatic and with mechanic self cleaning, is adequate for its set up and operation in a screening channel, width and deepness according to the attached drawings.
A maximum of m3 of waste water should pass through the step screen at a speed of m/seg, accordingly to the technical description.
The step screen should filter all materials and reduce to a minimum the charge loss that passes through it. The step screen should eliminate all the material with a diameter of more than 80 mm. The step screen displays a clean filtrating surface for the incoming flow.
Besides the wastes of small dimensions, the rest of the material, of size up to 80 mm, is automatically transported by the step screen to be deposited in the waste concentrator (supplied by separately).
The step screen is cleaned automatically by mechanical means. It also has a brush to eliminate the material deposited in a surface, obtaining a correct cleaning of the filtrating elements (B.O.P.I. U9701678 O patented system). Its operation is through a combination of toothed wheel of powering/discharge that powers the whole and eliminates the material, filtering the step screen.
The toothed wheel segments penetrate in the screen openings from the interior and push the wastes outside the elements. A scraping plate set up in the back part of the unit scrapes the particles and other adherent material as they accumulate through the screen openings. The unit uses flows of water to increase the efficacy of the cleaning. The step screen is clog proof and does not have jagged mechanisms.
The step screen does not require fixing elements in the lateral walls or in the bottom part of the channel. It can incline or be extracted from the coronation of the wall for its inspection or maintenance without emptying the water to the channel.
The step screen’s powering unit is performed by means of a hollow axis driver that will form a compact and hermetic unit.
The case is built in grey welding, the gears are manufactured in high resistance casehardened and tempered steel. The clients of the gears are rectified.
The electric engine is according to the standing standards and regulations as DIN-40050-VDE.0171.
The wiring ESTATOR VDM-0530, isolation F class, IP-55 protection and optionally, IP-68 three- phase alternating current 220/380-50 Hz.
Optionally, the equipment can be powered by means of an oleo hydraulic group.
All the damp and movable pieces or all the damp pieces to which movable parts are joint, such as the pivoting axis, step screen elements, rails, guides and structure, are completely corrosion resistant and are manufactured in AISI-304 or 316 stainless steel, except for the indicated ones. There is no filtrating plastic elements.
The lateral joints to the concrete channel are of neoprene with AISI-304 or 316 stainless steel bolsters. The guide rollers and spacing elements are of high impact resistance UHMWPS. Stainless steel or other material spacing rollers are not used, including the driving ones, etc. They are of corrosion resistant materials used by the manufacturer.
The guide UHMWPS rollers are slided over AISI-304 or 316 stainless steel rails. It has a stainless steel curved base in the lower part of the step screen in order to eliminate the need of a sump. No rolling, toothed wheels or submergible chains exist in the step screen.
The step screen is factory built- in and tested during at least 16 hours and is delivered completely built- in. It can be installed in site by the contractor with minimal operations.
The complete powering system formed by the engine, the driver and the rolling axis, are adequate for operating under specified environmental and service conditions.
For the adequate operation of the control and protection elements, a single reinforced polyester control box will be supplied of size enough to contain all the controls of the filtrating equipment.
The commands are a speed electronic changer, M-O-A power switches and luminous start / stop, indicators and terminal board for the step screen’s continuous operation. A luminous indicator should point out the existence of an alarm and immobility status. It should have the necessary relays to indicate the operation status and alarm, all these according to our technical sheet.
All the accomplished work and materials comply with electric and local regulations that apply. The client should care of obtaining the necessary permits, inspections and approvals of the competent authorities in the jurisdiction that corresponds to the working place, and assuming all the expenses.
The electric work is realized in agreement to the construction plan and progress in other fields. The electrical appliances of all the equipment are manipulated, built- in, connected, put to the test and placed for a satisfactory operation to the owner’s and the engineer’s satisfaction and within the scope of work described in this section.
All the pieces of the filtrating step screen that are not of stainless steel or plastic, are commercial pieces cleaned by SA-2 ½ sand flow and bear a coating and a finishing coating of the manufacturer’s standard paint.
Field tests, adjustments and starting up.
Once the installation is accomplished, the equipment must be checked and certified by an ESTRUAGUA representative, according to his recommendations and requisites. After such checking, a complete adjustment must be realized, and diverse components of the equipment will be put into operation under ESTRUAGUA’s supervision. The fulfillment of this services will need one day minimum.
All the equipment must be put into operation according to an appropriate plan, coordinated with the engineer.
It basically consists in a set of stainless steel plates (hooks) that connected between them form a moving step screen that submerged in the channel impedes the passing of the larger particles than the separation between them (see the attached catalog).
The efficacy in the solid separation is determined by:
1.1. The separation between plates, useful passes.
1.2. The step screen’s speed.
1.3. The speed of the water through the step screen.
2.1. The normal separation between purifier urban plates is from 6mm to 3 mm.
2.2. The step screen’s normal speed is of 4m/min. This speed can be fixed or variable.
2.3. The water speed through the filtrating plates is recommended not to exceed 1.5m/seg..
To obtain the maximum performance in the separation of solids, we will try to form in the step screen’s surface a mantle to filter the solids of the useful pass and the very inferior ones that will also be retained.
This function is attained with the collocation in the electric board of a double positioning timer, with which we can prefix both the start and the stop time.
With the step screen stopped, water passes through the plates, withholding solids that form a mantle, once the programmed time has passed, the step screen is powered raising the clogged zone and leaving a clean surface in the water. This process is continuously repeated, obtaining the maximum efficacy level.
A maximum level buoy will power the step screen, supposing that more dirtiness than normal will arrive and the programmed times would not be enough.
The step screen is normally supplied without the electric board, always including the scheme to include it in the general board.
As cleaning after the discharge, the step screen has a central tube system with diffusers that clean the step screen countercurrent.
It also has incorporated one or two revolving brushes, to obtain a correct cleaning between the screening elements, and maintaining that way the chosen bar spacing.
The step screen discharge can be carried out to :
– An endless transporting band or conveyor
– A hydraulic compactor
– A normalized container
– A transporting band
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