Direct coupling to fixed speed motors is common with non-slurry type centrifugal pumps. Duty variations are usually accommodated through changes in impeller diameter.
For slurry pumps, impellers are manufactured in hard metal white irons or metal reinforced elastomers. It is usually not economical or practical to reduce the diameter of standard impellers to meet specific duty requirements. Standard diameter slurry pump impellers are recommended for most abrasive applications.
The optimum pump speed, or speed range, can be achieved by suitable means, (for example, v-belt drive or variable speed drives), to meet the duty requirements. The lowest speed results in the lowest power consumption and the lowest wear rate for any given Muyuan slurry pump applied to a given duty.
Progressive speed changes are beneficial by providing the lowest practical pump speed to handle the required duty at any given time. On some duties, the required pump speed may have to be varied progressively, possibly over a relatively wide range,
★due to wear
★in order to maintain the intake static head at a constant value, or
★due to variations in required flow rate, static head, pipeline length exit pressure head or solids concentration,
Typical examples are:
★mill classifier(cyclone) feed in closed-circuit grinding operation, and
★some variable suction dredging duties.
For duties up to approximately 400hp, v-belt from a fixed-speed motor are commonly employed. The pump speed may be changed as required by occasional changes in sheave ratios (for example, a larger diameter motor pulley may be fitted). Where frequent variations are required, this solution is unattractive because the pump must be stopped to change speed and the speed change are stepped.
The most effective means of satisfying these progressively varying requirements is to provide for a efficient variable speed drive for either a mechanical or electronic design.
Where a motor size exceeds the practical limitations for v-belt applications, a direct coupled motor in conjunction with a speed reducing gear box may provide the most practical solutions.
Throttle valves are not recommended for use in slurry systems to control flow rate (by head loss), due to the resultant higher values of head, speed and wear on pumps and valves and due to the increased power required. An additional consideration is the increased risk of pipeline blockages.