Agriculture Reference
In-Depth Information
to reduce the suction head. The number of cylinders can be increased according to
power sources.
12.6.4 Displacement Pump
Displacement pumps force the water to move by displacement. This means pumps
such as piston pumps, diaphragm pumps, roller-tubes, and rotary pumps. These
pumps are used for moving very thick liquids, or creating very high pressures. They
are used in fertilizer injectors, spray pumps, air compressors, and hydraulic systems
for machinery. With the exception of fertilizer injectors (used for mixing fertilizer
into irrigation water), it is not typically used for irrigation systems.
12.6.5 Hydraulic Ram Pump
A hydraulic ram pump is a motor-less low flow rate pump. It uses the energy of
flowing water to operate. It is suitable for use where a large flow rate is not required.
The flow rate of typical commercially available units is limited to approximately 14
gal/min or 20,000 gal/day. The head produced by the pump depends on the quan-
tity and velocity of water flow at the pumping source. Water can be lifted up to
400 ft depending upon the quantity and velocity of water flow in the delivery pipe.
Hydraulic ram pumps can be used for domestic water supply or livestock watering.
Usually, their flow rates are too small to consider them for other applications, such
as irrigation.
12.6.6 Booster Pump
Booster pumps are used to increase the water pressure. Therefore the required
booster pump pressure is simply the desired pressure minus the existing pressure.
For most pump brands the pressure must be expressed in feet of head, not PSI.
PSI
×
2.31
=
feet head, Feet head
×
0.433
=
PSI
12.6.7 Variable Speed Pump
Many pumping systems require a variation of flow or pressure. Either the system
curve or the pump curve must be changed to get a different operating point. Where
a single pump has been installed for a range of duties, it will have been sized to
meet the greatest output demand. It will therefore usually be oversized, and will
be operating inefficiently for other duties. Consequently, there is an opportunity to
achieve an energy cost savings by using control methods, such as variable speed,
which reduce the power to drive the pump during the periods of reduced demand.
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