These electric powered pump systems control the speed of the motor/pump to provide the pressure and flow required. Prior to the existence of variable speed drives you either had to use expensive single stage pumps, or a pressure reducing valve, such as a Clayton valve. Whichever of these two systems were adopted, they still ran the motor/pump at full speed – regardless of what pressure and flow was required. With the Unico variable speed drive, the motor is turned at the speed that is needed and no more – rather like an engine driven pump.
When a standard motor is started, it can draw between 21/2 and 4 times its running current to start. A Unico variable speed drive slowly accelerates the motor and doesn’t draw any more current to start, than to run.
The energy savings created by the two factors above can be quite substantial. The larger the motor, the greater the saving. Also, when designing an all new pump house, as we don’t draw as much current from the electricity supply as a standard controlled motor, we can often use a smaller electricity transformer. For this reason and because the cables feeding the pump house can be smaller (as we don’t draw that massive starting current) there can be thousands of pounds saved.
Extra to the energy savings, the pipeline system benefits from the extra control gained by the variable speed drive. For example, as the motors are accelerated slowly, this gives the system time to build up pressure slowly as opposed to standard motor/pump systems where the motor/pump is running flat out at 2,950 RPM, forcing water into a pipeline at a great rate.
This causes two problems: A) During this pipe filling period, as the flow rate through the pump can be much higher than when the system is up to pressure, the pump can often be cavitating. This shortens the life of the pump. I am sure you will have heard a pump cavitating when it’s filling an open depressurised line. It sounds like gravel running through the pump. During these times, the pump should be throttled back either in speed or by a partially closed valve on the outlet of the pump, until the ‘gravel’ noise stops. B) Any trapped air on the system can be compressed to pressure much higher than the running pressure which can often result in a burst.
Unico manufactured variable speed drives have other advantages over their competitors. The panel and all its ‘components are manufactured or assembled by Unico UK. One company- whereas many of the competitors panels have parts assembled from several different suppliers.
This stops the ‘Peter blaming Paul’ problems. The Unico panel has a keypad on the front of the panel which allows the operator to make any adjustment to the program required. Most competitors use a programming person and a laptop computer to adjust program parameters. These control panels can also be retrofitted to existing electric pump house units.