Variable speed drives are used to provide a variable output speed from
a constant speed power source or to provide torque increase for a
variable speed power source. Variable speed drives that are designed for
dairy milking is as reliable as vacuum drives. They do not increase
milking time, nor they have any adverse impacts on cow health.
The benefits of using a variable speed drive includes:
- Lower cost - operating at less than capacity lowers
your energy draw. They have higher suction pressure, which is
more energy efficient.
- Reduced wear and tear - soft start increases the
lifespan of the equipment. Variable frequency drives turns the
compressor down rather than shutting it off resulting in less
wear and tear.
- Stable temperatures - they stabilize refrigerator's
temperatures.
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Advantages
- Often an inefficient bypass line can be eliminated.
- Throttling a pump discharge produces unwanted heat in a pump
that can be eliminated by changing the pump speed instead.
- The need for a throttling valve can be eliminated. Valves can
leak and require maintenance.
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Disadvantages
The pumps with variable speed drive shave several potential problems:
- The fluid viscosity can change with speed.
- The shaft can hit a critical speed on its way to the ideal
operating speed.
- Variable speed demands may affect the electrical power
distribution system.
- The mechanical seal has to be designed.
- The pump must be able to operate at reduced speed. A liquid
ring pump has can have trouble at lower speed.
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