Diaphragm Type Metering Pumps

Overview of how it works

The term positive displacement is used to describe an action that causes a fixed amount of something to be moved, displaced. The key word in the previous sentence is fixed. When dosing chemicals into your application, accuracy and repeatability in output are the most important factors. So having a pump that can produce a fixed output is crucial.

Positive displacement pumps utilize a cavity of some sort, and some kind of driving force to move the liquid. This is what allows it to produce the same amount of liquid over and over with each action.

With a diaphragm chemical metering pump, this action is the rearward and forward motion of a diaphragm which draws liquid in, and then pushes it back out of the cavity. In conjunction with a check ball valve at the inlet and outlet connections of the pump, this is how positive displacement diaphragm metering pumps produce an accurate and repeatable amount of liquid with each stroke.

(Check out this video we made for a previous article of a cut away chemical metering pump in action)

Why positive displacement is important

Accuracy and repeatability in chemical dosing are important for 3 main reasons.

  1. Cost savings
  2. Producing the right product
  3. Safety

Cost Savings

Chemicals can be very expensive and often times they are needed to be injected into a process 24/7/365. This can cost millions of dollars each year depending on your application. So procuring an accurate pump is crucial. Positive displacement type pumps, and specifically diaphragm chemical metering pumps, are the best for chemical dosing applications.

These pumps can be designed to hold up to the corrosive action of nearly any chemical, and remain very accurate for the entire course of their service live. Once the exact amount of liquid is known, or once the chemical dosing system is set up to read and respond to the exact amount of chemical needed, you can be confident your Madden chemical dosing pump will produce that amount of chemical with a +/- 1% accuracy.

Never wasting chemical, and thereby never wasting money.

Producing the right product

When your application needs a liquid injected into another process to produce a new substance, often times there is virtually no tolerance allowed. Meaning adding too much or too little of the chemical or liquid isn’t acceptable because it won’t result in the desired material/liquid the application is designed to produce. It may be “watered down” or the wrong new substance entirely when correct dosing proportions aren’t met.

Some examples of what you may want to result from adding a liquid/chemical into a process could be: acidic or basic water resulting in neutral water, like in wastewater treatment plants; it could be an entirely new chemical is needed to be produced, like in chemical producing facilities; or an entirely new product needs to be formed like all of the liquids that go into making glue or paint for example.

Point being, positive displacement type diaphragm metering pumps like Madden’s will ensure proper production


Don’t over think this point. Often times when dealing with chemical dosing applications, the application calls for the metering of dangerous and/or corrosive chemicals. These harsh chemicals can be very harmful when coming in contact with humans, as well as other machinery in the chemical dosing environment.

Positive displacement metering pumps offer safety via an enclosed, accurate pumping system. Get away from manually mixing chemicals in tanks and drums, and allow chemical metering pumps to inject the chemicals directly from the storage tank to the process’ injection point.

Keep employees and valuable equipment safe.

So that’s how positive displacement type diaphragm metering pumps work, as well as a bit of what benefits they offer.

Curious to see how they’re built?

Check out our sped up video of the entire building process, start to finish, of a Madden Pump MH series diaphragm chemical injection pump.



If you have an application needing an accurate, repeatable amount of liquid to be added to a process, please reach out to a Madden sales rep to inquire about our rugged, positive displacement type diaphragm metering pump.

With positive displacement pumps, accuracy is a given, that is why the design exists. With Madden positive displacement pumps, we add robust durability to our design; providing you an accurate chemical metering pump for years and years of service life.