Manual Screen :
Generally consists of flats say 50 x 10 mm or round bars of 10 or 12 mm diameter placed at an angle of 60º to horizontal - most convenient angle for raking.Used in screen channels.
Basket screen :
Closed from all five sides. Used for inlet pipe of raw sewage pumping station. For inlet lift station, the basket screen or the manual screen is placed vertical and is raised and lowered by using a chain pulley block.
Material of construction - MS / SS
Screen chamber upto
- 1 M deep - Rotary / Semirotary / Fine mesh
- 2 M deep - Semirotary
- 6 M deep - Inclined chain
- Beyond 6 M - Vertical grab
Curved rack bars are raked by a raking frame carrying the rake tynes and follows a semirotary motion.
- Less space for operation required due to its “SEMI” rotary movement as compared to rotary movement.
- Stainless steel material ensures very long life.
- Adjustable and spring loaded rake blade ensures minimum load on drive unit and prevents breakage.
- Replaceable rakes, part of rake can be replaced or altered
2. ROTARY SCREEN:
Bars curved, rake scraps the screenings by taking full rotation.
Since full rotation is taken by rake, more length of screen chamber is required. Cannot be used for deeper channels.
3.INCLINED SCREEN CHAIN TYPE :
- Raking, 3 to 5 times in one rotation of chain
- Angle of inclination − 75 − 85º to horizontal
- Easy installation since entire screen is factory assembled
4. FINE MESH SCREEN :
- For clear gaps upto 5 mm
- Versatile – Front screen type with a raised comb and rubber seal matches water ways with varying liquid levels.
- Compact – Screens are compact and lightweight.
- A rake frequently shuttles between both ends of the screen to prevent it from being clogged up.
- Economical and minimum running cost.
- Durable due to use of stainless steel material.
5. VERTICAL GRAB SCREEN :
- Any depth − no limitation.
- Sophisticated equipment
Latest trends :
- Use of inverter for motor facilitates adjustment of speed by adjusting frequency.
- Torque setting can be done using inverter for preventing overload.
- Dedicated electrical panel should be a prerequisite for timer control and operation of screen depending upon the liquid level by using differential level controllers. Operator errors and dependence on manual operating skill reduces.
- MOC − MS or SS 304 / SS 316 preferable, if MS is used then hot dip galvanize 100 µ, itching , primer coating followed by epoxy painting OR sand blast to SA 2.5, zinc spray 100µ, primer coating followed by epoxypainting.
- Shaft mounted gear box eliminates chain.