Water and fertilizer synchronization irrigation is a significant characteristic of drip
irrigation; fertilization device is one of main devices in the drip irrigation system. Venturi
injector is suitable for small drip irrigation system because of its simple structure, small
volume, low cost, simple operation, uniform fertilization. Based on the hydraulics principle,
the hydraulic performance was tested on Venturi injector of different structures. The
experiment was conducted to study on the energy conversion relation for different feature
sections, the influences of inlet and outlet pressure, flow velocity, and the coefficient of local
head loss on the negative pressure in the throat, the influences of the negative pressure in the
throat, inlet and outlet pressure, and inlet flow rate. And the major conclusion was obtained:
（1）At present, the throat structure of Venturi injector is central symmetric, the
coefficient of local head loss is great. Now, the structure of Venturi injector was improved.
Leave the throat diameter as is but change the structure that central symmetric to upward
eccentric, and the angle of shrink and magnification shall be reduced by half. In order to do
this, the coefficient of local head loss was decreased.
（2）The throat negative pressure was no longer influenced by the inlet pressure head
and the head loss increased sharply when the throat negative pressure reached the minimum
value. The differences between the actual and the theoretical flow rate reflected the throat
vacuum space size, the actual flow rate increased significantly and the kinetic energy in the
throat also increased being similar to a parabolic shape when the throat negative pressure
reached the minimum value. The head loss (energy loss) increased sharply as the flow rate
increased when the water flowed through the Venturi injector. The more the inlet pressure
increased, the greater the energy loss. The starting pressure of the throat generating the
negative pressure increased and the flow rate was relatively large under non-free-outflow
conditions. The inlet pressure and the flow rate under non-free-outflow conditions were
significantly higher than that of free-outflow conditions based on the same negative pressure.
（3）The generation of the negative pressure in the throat was related to inlet and outlet
pressure, with the increment of outlet pressure, higher inlet pressure was required to generate
negative pressure and reached the minimum. The negative pressure in the throat had a
significant linear negative correlation with inlet pressure. When the negative pressure reached the minimum value, the value of negative pressure was stable as the inlet pressure increases.
Flow velocity had similar effects with pressure on the generation and dynamics of negative
pressure. When the coefficient of local head loss was the same, at the same inlet pressure, the
same flow velocity had the same negative pressure, the greater the throat diameter, the greater
the flow rate of the needed throat negative pressure to achieve the target; For the different
coefficient of local head loss, the higher the value, the decrease speed was slower of negative
pressure in the throat as the inlet pressure increased, the greater of the needed throat negative
pressure to achieve the target.
（4）The injection rate of Venturi injector increased with the increasing of the inlet
pressure and the inlet flow rate at the initial stage. When the injection rate reaches the
maximum value, the injection rate was stable as the inlet pressure and inlet flow rate
increased; the injection concentration increased first, then decreased with the increasing of the
inlet pressure and the inlet flow rate. The injection concentration reached the maximum value
that was about 12%~13% when the negative pressure reached the minimum value.
（5）Pipeline design of Venturi injector in the drip irrigation system was improved. The
minimum inlet pressure needed and the formula of the critical velocity of the throat to achieve
absorbing fertilizer under different outlet pressures were put forward. On this basis, the paper
had come up with a method of reasonable selection of Venturi injector in the drip irrigation
system, In order to ensure uniform of velocity, the paper present a new method about the
pipeline design of Venturi injector in the drip irrigation system.
Keywords: Drip irrigation system; Venturi injector; Energy conversion relation; Negative
pressure; Injection performance