Madden Manufacturing • June 17, 2014
A number of factors need to be considered when specifying a metering pump, so we have prepared a list to help satisfy the needs of your application.
At Madden, the first thing we want to know when we’re talking to a customer about specifying a metering pump is what chemical or liquid is going to be pumped. The nature of the liquid will help us determine what materials of construction are appropriate for pumping as we want the pump materials to resist the attack of dangerous or corrosive liquids. As you can imagine chemical leaks and spills can be a mess to clean up, and they can cause serious health and environmental problems, so having the right materials for the wetted end of the pump is vital. In the Madden diaphragm type metering pump the wetted end consists of the following items:
- Solution head: this element can be either metal or plastic. The solution head provides a chamber for the diaphragm to fill and empty out the liquid being pumped.
- Diaphragm: a variety of fabric reinforced rubber diaphragms are available to resist the chemical action of the liquid. The diaphragm is the element of the pump that pulls and pushes on the liquid, and the diaphragm keeps the liquid out of the mechanical section of the pump.
- Valve check balls: a diaphragm type metering pump has ball type check valves on the suction and discharge side of the solution head. The suction side valve permits liquid to enter the solution head on the suction stroke, and seals the suction end on the discharge stroke. The discharge side valve does just the opposite, closing on the suction stroke and opening on the discharge stroke. Check balls are available in ceramic, Teflon, 316 stainless steel and Hastelloy C, as well as other less common materials.
- Valve body, seat and gaskets: the body of the valve is generally the same material as the solution head. Valve seats can be Teflon, or a rubber material matching the diaphragm material. Some liquids, such as diatomaceous earth suspensions, are abrasive, requiring stainless steel or ceramic valve seats to resist the wear.
- Backup diaphragm: pumping dangerous liquids requires extra security against leaks. We recommend the double diaphragm construction for the wetted end in these situations. The backup diaphragm will generally be the same material as the primary diaphragm that contacts the liquid being pumped.
So how do we know what material to specify for these elements of the metering pump wetted end? We suggest consulting a chemical resistance guide. Madden has prepared a guide of the most commonly pumped liquids . You can also go on line and find guides, for example: http://www.coleparmer.com/Chemical-Resistance
. Finding appropriate materials for the liquid is a start and the pump manufacturer can help refine the selection based on cost and durability. For additional help in specifying your metering pump consult the Madden Pump Selection Guide
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