Tuesday, February 22, 2011

Special VFC’s for Constant Pressure Systems

For sometime now, we have been involved with one of our suppliers selling a Variable Frequency Controller with several special features for running a "Stand-Alone" system to ran a pump for constant pressure.
This VFC has built-in PID for pressure regulation and also has a built-in “Sleep Mode”.  What Sleep Mode does is when the system requirements are met and there is no need to pump water, the VFC simply shuts down and waits for the system to call for pressure again.  The drive then wakes up and starts delivering water into the system again.  This is not necessarily unique.  A few other drive manufacturers offer this as well, but they do not have the flexibility that we have for setting on and off pressures and an unsurpassed PID function.  We also have special ramp capabilities that we can program in for special pump considerations.

Another thing we do is that we can drive the control signal with the built-in 24 VDC power supply on board the drive.  This makes it so you only need to add a 2-wire pressure transducer to the drive and you have all you need to make the system work.

We have done this for many customers.  Farmers particularly like this system, as no matter how many sections of either hand-line or wheel-line they connect up to the water source, the drive will maintain constant pressure through the system for even water distribution up to the systems maximum rating.  And do to the sleep mode function, there is no need to run to the well and shut it off.  The VFC is always ready in sleep mode waiting for a call for water.  Just open a valve located on the main system line and the VFC comes to life and produces water from the source.

We have a well at our house, which is our only source of water.  We have been running a drive on it for the past 8 years and it is wonderful.  We used to set out a sprinkler to water the lawn and it would go up and down with the pressure, as the pump would turn on and off to meet the demand.  Now, it is just like being hooked up to the city water only better because I’m in control.

In our area, to develop property for almost any use you need to secure the water rights that come along with the property for secondary irrigation.  We have installed many units just for this need with great success.  Many a subdivision, apartment complex and townhouse village is being irrigated by one or more of our drives.

The single phase input units are used quite extensively in these applications, as most areas do not have three-phase power available.  Most of these units we build-up in a NEMA 3R Enclosure with a fused disconnect, input line reactor and a DV/DT filter so as not to disturb the lines in the area do to harmonic issues caused by the drive.  This is especially needed in a residential application and works very well.

Some of our customers that have used this are mostly pump installers such as Widdison Turbine Service, Zimmerman Well Service, Nickerson Pump Company and many others.  If you have a need for something like this or know someone who may benefit from this type of system, give us a call.

Scott Gordon

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