Specifying the motor and controller are both required when a specifying an automatic metering pump. We have prepared the following list to help you make the motor and controller choice that will satisfy the needs of your application.
In our previous blog articles on specifying a metering pump we stressed the importance of matching the liquid to be pumped with wetted end materials of construction that can safely and economically handle the liquid. We also discussed the electrical drive motor options for a metering pump. In order for the pump to do its work automatically Madden pumps use a variable speed motor and a controller.
Here are some thoughts to take into consideration as you are specifying a motor and controller for an automatic metering pump:
- Madden diaphragm metering pumps come equipped with a manual output adjustment knob located on the top of the pump for easy access. The Madden pumps can be adjusted over a 10:1 turndown range by using the adjustment knob. So for a 60 gallon per hour pump, for example, the manual output range would be from 6 to 60 gallons per hour. To prevent damage to the stroke adjustment mechanism, the adjustment knob should only be turned when the motor and pump are operating.
- But what about controlling the pump output automatically? Madden pump output changes very linearly with the change in the drive motor rpm. If a 60 gallon per hour pump motor is running at 1,725 rpm, by reducing the motor speed to 862 rpm the pump output will drop to 30 gallons per hour.
- There are two basic variable speed drive systems: AC and DC. The AC system requires an inverter duty variable speed motor, and an AC variable frequency drive (VFD). The VFD can change the normal 60 Hz current frequency down to 6 Hz, and by changing the voltage with the frequency being supplied to the motor the motor speed is changed. VFD’s are available in 1/60/115-230 and 3/60/230-460 factory power supply. They can also be used with 50 Hz power. The KB Electronics VFDs Madden uses come with a NEMA 4X water tight enclosure and an installed 4-20 mA signal follower. An option for the controller is a remote/local selector switch.
- The DC system requires a 90v DC variable speed motor, and a DC variable speed drive (VSD). The VSD can change the DC voltage from 90 volts down to 9 volts, and by changing the voltage being supplied to the motor the motor speed is changed and with the change in motor speed the output of the pump changes. VSDs are available for 1/50-60/115 and 1/50-60/230 AC electrical factory power supply. The KB Electronics VSDs come with a NEMA 4X water tight enclosure and an installed 4-20 mA signal follower. An option for the controller is a remote/local selector switch.
- Automatic pump output control comes from a 4-20 mA signal that tells the VFD or VSD to change its output and the corresponding motor speed and pump output. An instrument or a computer can be used to generate the 4-20 mA control signal by tracking a value of plant system operation. As the instrument measures a higher or lower system value the instrument sends a 4-20 mA signal to the VFD or VSD.
- Whether AC or DC variable speed, it should be noted that Madden pumps operate best with stroking speeds from 15-230 strokes per minute. Speeding up a pump or slowing it down outside that range can impact the pump performance.
- Variable speed motors are available as the standard totally enclosed motor, or optional washdown duty and explosion proof motor enclosures are also available to meet any special requirements for the environment where the installed pump will be.
These are just some of the factors to consider when specifying a motor and controller for an automatic metering pump. For more information on the KB Electronics VFDs click on this link. For additional help in specifying a metering pump for your application, consult the Madden Pump Selection Guide on our website, call us, or send us an email inquiry. We are always quick to respond.