By: Kate
Email:kate@aquasust.com
Date: 11th March 2025
The Valve A valve with a bridge setting controls the sequence of the cycle so that each sector is subjected to vacuum, blow and a dead zone. When a sector enters submergence vacuum commences and continues through washing, if required, to a point that it is cut-off and blow takes place to assist in discharging the cake. The valve has on certain filters adjustable blocks and on others a fixed bridge ring. Adjustable bridge blocks enable the optimization of form to dry ratio within the filtration cycle as well as the "effective submergence" of the drum when the slurry level in the tank is at the maximum.
The majority of drum filters have a valve with three bridge blocks and a single row pipe plate as shown below and on the right. 1. Vacuum and blow zones separating bridge. This bridge cuts off the vacuum so it is slightly wider than the internal pipe port. 2. Dead zone bridge. This bridge opens to vacuum once a compartment submerges. 3. Start-up assist bridge. At start-up the upper vacuum zone is open to atmosphere and a cake may be formed only when closing the valve that controls this zone. Once the cake starts to emerge from the tank the valve is gradually opened and fully opened when the entire drum face is wrapped with the cake. Since in continuous operation both lower and upper zones are under vacuum this bridge is slightly narrower than the internal pipe port so that the vacuum is continuous and the cake is held onto the drum.
The filter cloth retains the cake and is fastened to the drum face by inserting special caulking ropes into the grooved division strips. Nowadays, with some exceptions, they are made from synthetic materials such as polypropylene or polyester with monofilament or multifilament yarns and with sophisticated weaves and layers. The image on the right shows the method of joining the cloth ends with clippers and to retain the fines from passing through to the filtrate multifilament strings are threaded across the entire cloth width. Another option quite often used on belt discharge filters is to join the ends with a special sewing machine.
The Agitator An agitator keeps gently the slurry in suspension and reciprocates between the drum face and tank bottom at 16 or so CPM. The Tank The tank that houses the drum and agitator has baffled slurry feed connections, an adjustable overflow box to set a desired drum submergence and a drain connection. The tanks are normally designed for an "apparent submergence" of 33-35% however on certain applications 50% and more is possible. With these special designs the tank ends are higher in order to accommodate stuffing boxes on both the drive shaft and valve end trunnion. The Cake Washing Manifold On applications where cake washing is required, 2 or 3 manifolds with overlapping nozzles are mounted to a pair of splash guards bolted to the tank ends. The position of the manifolds and the quantity of wash liquid are adjustable depending on the wash characteristics of the cake.
Control Instrumentation
Optional controls may be used to automate settings such as drum speed, applied wash liquid and drum submergence for a desired cake thickness or throughput. The monitoring of drum submergence controls the slurry feed valves so an adjustable overflow weir is not necessary except for a fixed connection in case of emergency. To learn more about what this system might look like for your facility, request an Drum Filter quote today. You can also contact a representative who would be happy to answer your questions concerning Drum Filter and other wastewater treatment methods. Aquasust is a company you can trust for the very best in modern wastewater treatment plant equipment.