In addition to specifying the required flow rate and pressure to be pumped, the drive motor needs to be considered when a specifying a metering pump. We have prepared the following list to help you make the motor 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 liquid flow requirements. In order for the pump to do its work it needs a source of power.
Here are some thoughts to take into consideration as you are specifying a motor for a metering pump:
- Electrical power available in the US: we need to match the motor with the plant electrical power. In the US the common electrical power is either single phase 1/60/115-230 or three phase 3/60/230-460. Three phase 208, 480 and 600 volt power is not uncommon. Most often the 1/3 HP motors used on many of the Madden pumps will be single phase. When ½ HP and larger motors are required for a specific pump model previously selected to handle the required flow rate and pressure the preferred motor is often 3 phase. The important factor is what electrical power is available at the installation site where the pump is going to be installed? You might be surprised, but it is not uncommon for a customer to receive a pump and have to call us to exchange a motor because the wrong power had been specified when the pump was ordered.
- Electrical power available in other countries: while many countries have 60 Hz electrical power like the US, many other countries have 50 Hz power available. Single phase 1/50/110-220 and three phase 3/50/380 are common power specifications. It is essential to specify the correct electrical power for the pump motor. When 50 Hz power is used the motor rpm for a single speed motor is 1,425 rpm, significantly lower than the 1,725 rpm that a 60 Hz motor produces. This motor 50 Hz motor speed discrepancy reduces the output capacity of a pump resulting in 83% of the capacity of a pump operating with a 60 Hz motor.
- Motor enclosure: the standard motor enclosure that Madden uses is TEFC (totally enclosed fan cooled). For pumps that operate in difficult environments other enclosures may be specified: explosion proof, wash down duty, or mill and chemical plant duty. Specifying the correct enclosure is important for safety as well as motor service life considerations.
- Alternative motors: occasionally we get requests for direct current DC motors operating at 12 and 24 volts for use on mobile equipment, as well as 90 volts for use with variable speed drives. Air motors are also requested, particularly for use in explosion proof applications.
- Variable speed motors: these are often used to provide automatic pump output control. Madden diaphragm metering pumps come equipped with a manual output adjustment knob. For automatic pump flow control we use a variable speed variable frequency AC motor powered by a variable frequency drive. The variable frequency drive is equipped with a remote signal follower that will change the motor rpm and the corresponding pump output in response to a change in a 4-20 mA signal or other process signal sent to it from an instrument or computer. Variable speed DC motors and controllers are also available to accomplish the same automatic pump output control. 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.
These are just some of the factors to consider when specifying a motor for a metering pump. We will discuss additional elements in future blog articles. For additional help in specifying a metering pump for your application, consult the Madden Pump Selection Guide on our website or click here to send us an email inquiry. We are always quick to respond.