How do we specify the requirements of a metering pump if we don’t know much about metering pump construction? We have prepared the following list to help you understand the elements of a metering pump to help the pump specifier to document 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 and accessory options for a metering pump. Here are some thoughts to help you understand the four major components of construction of a metering pump:
- Wetted end: this is the section of the pump that comes in contact with the liquid that will be pumped. For the Madden diaphragm type metering pumps this consists of the solution head, the diaphragm, the inlet and outlet check valves and the piping connectors. All of these components need to be compatible with the liquid that will be pumped. Madden and other metering pump manufacturers like LMI, Milton-Roy and Pulsafeeder offer a wide range of materials for the wetted end construction to allow the pump specifier to select the right materials for each pumping application. For a more compete discussion of the wetted end see our blog Specifying Metering Pumps. Piston or plunger type metering pumps do not use a diaphragm to separate the liquid in the wetted end from the drive mechanism. Those pumps use a packing gland for the purpose of containing the liquid.
- Drive system: this section takes the rotary power of an electric motor and converts it into a piston stroking action. Madden and many other metering pump manufacturers use a right angle worm gear reducer to convert the 1725 rpm electric motor speed to a stroking speed ranging from 15 to 230 strokes per minute in different pump models. The gear ratio used in the worm gear reducer will determine the stroke speed; i.e. a 10:1 gear ratio will reduce the 1725 rpm motor speed to 172 strokes per minute drive shaft speed. The connecting rod and piston are driven by the drive shaft. As the drive shaft rotates the connecting rod, and the attached piston, will make a stroke in and out, driving the diaphragm in the wetted end which moves the liquid being pumped. Madden uses heavy duty industrial grade worm gear reducers to insure many years of trouble free pumping service. The Madden pumps are mechanically actuated diaphragm type, so the piston is directly connected to the diaphragm in the wetted end. Other manufactures use a hydraulic system to push and pull the diaphragm. Some manufactures of smaller metering pumps do away with a gear reducer altogether and use an electric solenoid stroking mechanism to activate the metering pump piston.
- Electric motor: most Madden diaphragm metering pumps use an electric motor for the power to operate the pump. Stock motors for Madden are from 1/3 HP to 1-1/2 HP, 56 frame, totally enclosed, with both 1/60/115-230 and 3/60/230-460 voltages available. Special motors are available for a wide range of applications from 50 Hz power to explosion proof and high altitude installations. For a complete discussion of motors see our blog on Drive Motor Requirements and Drive Motor Specifying Automatic Metering Pump.
- Output adjustment: the Madden diaphragm metering pumps are manually adjustable using a conveniently placed adjustment knob located on top of the pump. The adjustment goes from 100% down to 0%, but for the most accurate volume control 10% is the minimum recommended adjustment setting. The Madden adjustment is a lost motion type, which means that for any adjustment setting below 100 the diaphragm is not powered by the piston over a portion of the rotation of the drive shaft. Some manufactures use a hydraulic drive and reduce the stroke volume in the hydraulic section with a lost motion action. There are pumps on the market that offer an adjustable eccentric for controlling the output, and some of these require the use of tools to change the eccentric setting when the pump is stopped. Electronic solenoid type metering pumps can manually reduce the stroke rate with an adjustment knob, or they can actuate the solenoid with a remote pulse signal. For information on Madden metering pumps using an automatic output control see the blog Drive Motor Specifying Automatic Metering Pump. The important thing to know is that the pump you specify will have the capacity in the range of adjustment to accurately pump the required liquid volume, and that the adjustment of volume is easy to accomplish.
Those are the major component elements to consider when specifying a metering pump. 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.