Tasked with devising a control system that would maintain this constant delivery pressure despite variations in pressure in the water supply, which is derived from a storage tank fed with spring water, ST Controls opted for a pumped water delivery system, with the pump controlled by a VACON variable speed drive with a 31A continuous current rating. 

The drive is used in conjunction with a custom control panel designed and constructed by ST Controls. This incorporates a touch-screen panel giving users access to operational features such as the time for which the washdown system operates.

When washdown is needed, the VACON drive provides a controlled ramp up of the pump speed and, when the required delivery pressure is reached, the control panel operates a solenoid valve that allows water into the manifolds that feed the 64 washdown nozzles. 

Throughout the washdown period, which is typically set to last around 10 seconds, the water delivery pressure is monitored by a transducer and, using the internal PID controller of the drive, the pump speed is modulated to ensure that the pressure is accurately maintained at the 6 bar level needed for optimum sanitising. At the end of the washdown, the pump speed is ramped down to zero, and the water delivery solenoid closed.

Two further VACON drives, rated at 9 and 31A, are used in the milking parlour installation. The first powers a secondary washwater pump that supplies a PID controlled pressure of 8 bar to manual washdown hoses that are available for ad-hoc cleaning throughout the milking parlour, while the second 31A drive powers the hydraulic pump that operates the gates used to retain the animals safely and comfortably in their stalls while they are being milked.

Like the main drive, these ancillary drives are configured to provide ramped starting, stopping and automatic speed control of the pumps. This not only has the benefit of reducing stress on the pumps, pipework and other systems, it also reduces the current surge when the pump motors start, which is an important requirement as the electricity supply to the farm, as is typical in rural locations, has only limited capacity.

“Also, by using the IP54 versions we were able to mount them on the wall next to our control panel rather than inside the panel. This made the panel smaller and lower in cost, as well as meaning that we didn’t have to make provision for getting the heat from the drives out of the panel. Finally, of course, VACON is a great company to work with – we rarely need support but, when we do, it’s always readily available and spot on target.”

The drives proved easy to install, set up and commission and the system worked exactly as planned from the outset. It has now been in use for several months, and has been entirely problem free in operation.