Source: Ing. Werner Meixner
To stir the manure Pumps and agitators in a wide variety of designs. It is important for farmers to know the technical limitations and advantages of these systems.
Manure should always be stirred before spreading. If the settling and alluvial layers are not removed, the usable volume of the manure tank will gradually decrease. Furthermore, the individual layers of non-homogenized manure differ in their nutrient composition, making targeted, even fertilization difficult.
However, not all manure is the same. Pig and cattle slurry differ significantly in their physical properties. Due to the high proportion of specifically light organic components, cattle slurry primarily forms floating layers, while pig slurry, with its heavier particles, forms sediment layers. However, these sediment layers are difficult to mix into the liquid slurry, requiring correspondingly high levels of effort.
According to various practical tests, it is sufficient to maintain a minimum flow velocity of 0.2 m/sec when mixing the cattle manure.
For pig slurry with its existing settling layers, the required velocity is at least 0.5 m/sec. Pig slurry has another disadvantage: the solid organic components settle quickly. Sediment forms again within an hour of stirring.
With cattle manure, however, it takes days for a new floating layer to form.
Stirring by pumping
Settling layers can only be partially broken up by pumping. The upper limit of the slurry tank at which sufficient flow velocities can still be achieved is 400 m³ for pig slurry. For cattle slurry, the storage tank can be larger.
The advantage of mixing slurry with pump systems is that they are relatively inexpensive, as many farms already have suitable pumps. They can also be used to empty slurry tanks. Both mobile and stationary operation of the pump is possible. These are primarily used Rod, progressing cavity or rotary lobe pumps.
In submersible pumps located in the slurry, an electric motor is flanged directly to the pump. The absence of friction losses in the pipes creates a stronger agitation jet and thus better mixing of the slurry.
Stirring by agitators
Agitators operate with slow-speed blades, reels, or paddles and high-speed propellers. The latter have become the standard for manure handling and are also suitable for manure tanks larger than 400m³. These can be powered either electrically or via the tractor's PTO. In electrically powered agitators, the motor is usually located directly next to the propeller, meaning that the propeller submerges into the manure along with the agitator.
A disadvantage is the comparatively high electrical connection load and the somewhat higher purchase price. Furthermore, these agitators are usually less powerful than PTO-driven agitators, as they have smaller diameters or operate at a lower speed. However, these agitators do not block a tractor, are very compact, and can be operated without supervision.
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