Water flow resistance of water treatment system equipment

When water flows through necks, valves, tees, elbows and other components, resistance is generated, which is called local resistance. The main purpose of calculating the water flow resistance of the water treatment system equipment is to reasonably select the head of the water pump and determine the elevation of the outlet pipe of the clarifier (including the sedimentation tank) under the condition of gravity, so as to overcome the various resistances of the filter tank at a suitable elevation and ensure the normal operation of the system.

1. System flow resistance

  1. Pipe resistance
  2. Local resistance
    When water flows through necks, valves, tees, elbows and other components, resistance is generated, which is called local resistance.
  3. Head loss in sludge pipeline
    In the turbulent state, when the moisture content of the sludge is greater than 98%, the head loss of the sludge pipeline can be set as 2 to 4 times that of the clean water; when the water content is 90%-92%, the head loss of the sludge pipeline can be set as 6-8 times that of the clean water.
  4. Local resistance coefficient of orifice plate

2. Equipment resistance loss

In addition to the system pipeline resistance loss, the equipment resistance loss includes the resistance of flow meters, filters, ion exchangers, and membrane treatment system equipment.

1. Flow meter

There are many types of flowmeters, among which differential pressure orifice flowmeters are commonly used for water treatment. The resistance loss at the normal design flow value of each pressure orifice flowmeter is about 5mH2O. (50kPa), pay attention to leave a certain margin. You can also refer to the local resistance coefficient of the orifice plate in Table 8-12, and calculate the local resistance hj of the orifice flowmeter at the maximum operating flow rate. When installing the differential pressure orifice flowmeter, a straight pipe distance of 10 times the pipe diameter upstream of the orifice plate and 6 times the pipe diameter downstream should be maintained.

2. Filter layer resistance loss

The filtration process of a filter bed composed of granular materials is extremely complex, and its head loss cannot be accurately calculated. Especially for the filter, during the operation process, from the clean filter layer to the filter tank after the dirt is intercepted, the porosity of the filter layer decreases due to the interception of suspended solids, and the resistance loss gradually increases. The head loss of a clogged filter layer is a function of the filtration time t. That is to say, the head loss of the blocked filter layer is equal to the head loss of the clean filter layer multiplied by the coefficient of the increase of the head loss caused by the blockage of the filter layer by suspended impurities. Mainly limit the filter layer resistance for the filter, such as the head loss before flushing of the valveless filter, generally adopt I. 5m (15kPa). The pressure filter generally limits the inlet and outlet pressure difference at 3^-5m (30-50kPa) to shut down and flush.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading

Commercial Water Treatment System

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