What is head loss in a filter?
Loss of Head Indicator As filtration proceeds, an increasing amount of pressure, called head loss across the filter, is required to force the water through the filter. Head loss should be continuously measured to help determine when the filter should be backwashed.
What is head loss in a sand filter?
Head Loss: It requires energy for water to pass through the filter. This energy in a rapid sand filter is usually in the form of head pressure—basically the weight of the water on top of the filter bed. This loss of energy during the filtration process is known as head loss.
What is the maximum limit of head loss in sand filter?
2 to 5 m.
Maximum loss of head = 2 to 5 m. Spacing of laterals = 15 to 30 cm c/c.
Why is head loss important?
The head loss also represents the energy used in overcoming friction caused by the walls of the pipe and other technological equipments. The head loss is unavoidable in real moving fluids.
Why does head decrease with flow rate?
Increasing flow rate introduces friction into the system as the liquid travels along the pipes from the suction tank to the pump and from the pump into the discharge pipe. In fact, as the flow increases, friction increases and the total head continues to decrease.
What is head loss?
The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, or fittings. Water flowing in a pipe loses head as a result of friction losses.
How often should a slow sand filter be cleaned?
A rapid sand filter is maintained and cleaned by forcefully injecting water backwards through the entire sand bed every 2 or 3 days. Backwashing a biological sand filter will destroy it and may result in people getting very sick if water from it is being consumed.
How do you calculate major head loss?
Darcy-Weisbach Equation+
- Δh = the head loss due to friction (m)
- fD = the Darcy friction factor (unitless)
- L = the pipe length (m)
- D = the hydraulic diameter of the pipe D (m)
- g = the gravitational constant (m/s2)
- V = the mean flow velocity V (m/s)
What is pump head loss?
Head loss refers to the total pressure losses sustained by the fluid as it flows from the suction point to the discharge point. It is important to be able to work out the head loss that will be incurred within an installation in order to be able to determine the pressure required by the pump to operate efficiently.
What would happen if the backwash rate is too high?
If backwash rates are too high, significantly more media could vanish—compromising filter performance. This occurs when water flows upward at sufficient rate to fluidize the media bed, increasing the space between the media grains and causing the media to ”expand”, or occupy more volume.
What is the permissible negative head loss of a rapid sand filter?
0.8-1.2m.
Explanation: The permissible negative head loss of a rapid sand filter is 0.8-1.2m. When the permissible limits are reached, the filter run is terminated and the filter is back washed.
How does pressure loss in a filter bed work?
Pressure curves in a filter bed Once the filter has been commissioned and using clean, homogenous sand, according to Darcy’s law, the head loss will be proportional to the depth of the sand and to the flow rate, deemed constant for the purpose of this analysis.
What should the head loss of a water filter be?
In order to maintain an acceptable quality of filtered water, the filter must reach is head loss P 2 at time (t 2) before breaking through at time (t 1 ), i.e. t 1 > t 2.
What happens when you use a sand filter?
The fine sand contained in the top layers of the filter bed shrinks and causes the development of shrinkage cracks in the sand bed. With the use of filter, the loss of head and, therefore, pressure on the sand bed goes on increasing, which further goes on widening these cracks.
How is water filtered through a granular bed?
The water to be filtered percolates through a filter bed made up of one or more types of granular materials; the properties of these materials and the bed depth must be adjusted according to the water to be treated and the type of filter selected.
