Matching water flow and pressure with pipe size

Flow in pipes is defined as functions of dimension of pipes and velocity of flow. While determining dimension of pipe in irrigation system investment costs can be minimized through choosing the possible smallest dimension of pipe. However keep in mind that reducing dimension of pipe shall increase the velocity as seen in following formula. Increase of velocity means increase of loss of frictions occurring in pipes.

Q=A*V (19)

Where.

Q:system flow (m3/h)

A: line cross-section area: m2 V: velocity of flow. m/s

Possible minimum dimension of head should be chosen according to limitations of friction loss which are allowed. While choosing dimension of main pipe it is required not to exceed 15% of pressure of pumper. Pressure difference between starting and ending point in lateral shouldn’t be over 20%. Also total head losses in system shouldn’t exceed half of orifice pressure.

5.4 Total dynamic head of the system and power requirement

Pressure which is necessary for irrigation system is generally carried out through a pump installed at the beginning of system excluding the situations in which adequate elevation is not available between resource and irrigation area. Pump should be chosen at power which provides optimum pressure in the last head in the line which is called as critical line and has head losses at excessive rate in this system. Total dynamic height of pump in a system is calculated by means of following formula;

Ht=hs+hh+he+hsuc (20)

Where.

Ht: total dynamic head of pump, m hs: sprinkler operation pressure, m. hh: total head losses, m.

he: elevation difference between highest point in irrigated area and pump, m

hsuc: suction line height if there is elevation difference between pump and water supply

suction line height should be considered.

Also engine power of pump is required to be determined. Pumping Energy which is appropriate for system is determined by means of following formula.

Np=Ht*Q/75* p1p2 (21)

Where.

Np:Pump power, HP Ht: Total head loss, m.

Q:system capacity, l/s pi: pump efficieny, % p2: driver efficieny, %

Pumps which provide necessary pumping power are included in system by help of catalogues of relevant firms.

6. Conclusion

Irrigation is one of the main factors on plant growth and quality. Irrigation is applied in areas where evapotranspiration is not met by rain especially in semi-arid or arid climate. Pressurized irrigation methods are used generally in landscape irrigation.

The most common method between pressured irrigation methods is sprinkler irrigation method. Sprinkler irrigation method is preferred by reasons such as providing high corresponding water distribution, its use easily in any kind of soil and area where plants are grown, its low labor costs and fertilization proceeding’s being easily applied. Determining system units completely according to requirements in project step provides system performance being in high level. Drip and micro sprinkler irrigation methods should be considered as an alternative method in where sprinkler irrigation system is inadequate or ineffective.

Updated: October 17, 2015 — 11:34 am