Which factor influences the selection of the right valve for fully automating an STP/ETP?

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Should we go for a pneumatic/motorized ?

Should we go for ball valve/ butterfly/ solenoid valve ?

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4 Answers

  1. Hi Vishnu,

    Valves types depend on the fluid application and several physical factors (pressure, allowable pressure drop, flow regulation/open-close application, turbulence, throttling, and flowrate). The ball/butterfly/gate valve/solenoid is intended for open-close only application and to cope with high pressure while needle valve is to regulate flow. There are many others types of valves (an example is within this link: https://megadepot.com/resource/a-guide-to-types-of-valves)

    So to answer your question, particular application/physical condition in your STP/ETP need to be considered and which part of STP/ETP process.

    Meanwhile pneumatic control is used for open-closed application  and motorized is used when you need to control the openness of the valve chamber to regulate flow/pressure.

  2. Process is not given. Most of the time flow in conventional STP is by gravity from screen chamber to the treated sewage storage tank.

    Valves are mainly required on following pipe lines

    1. Raw sewage pump delivery line
    2. Sludge handling pipe line for primary clarifier
    3. Re-circulation line for re-circulation of water from Secondary clarifier to aeration tank

    If IL of sewer line is far below the ground level then sewage is pumped from sewage sump to the first unit operation.

    Performance of motorized and pneumatic valve is good. Selection of the valve depends on site condition.

    I personally preferred butterfly valve for sewage & sludge handling.

    Prof. Rajendrakumar V Saraf

  3. Dear Vishnu,

    Regarding the valve drives, I would recommend electropneumatic drives (piston or diaphragm type) with solenoid valves (on air side) for open/close applications and with electropneumatic positioners for modulating applications. These are far more reliable compared to electrical servomotor drives and less expensive inluding air compressors and dryer when you have 3 or more valves.

    Regarding the valves I would recommend full bore ball valves for diameters up to DN50 (2") and butterfly valves for larger diameters in most applications. For thick sludge containing fibers (hairs, ...) the butterfly valves shall best be replaced by knife valves.

    For pressurized clean water or air and small diameters solenoid valves can be used.

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  4. Oddly enough, it may depend more on the air environment near this valve than the water environment through the valve.  Sewage gases corrode wiring so fast, maybe I would consider an air-operated system.  The actual valve type depends on on/off characteristics, if it is needed for regulation of system flow or pressure, etc.

    1 Comment

    1. but if its a sewage treatment plant for a residential area, where i imagine its a practically safe area from corroding gases ( I assumed only the formation of CO2 gases from the plant) because here in India most of the population choose aerobic bio treatment than anaerobic. Lets say for controlling just the flow in a pressurized line . would you suggest a air-operated butterfly valve or a electrically-operated system?