The closeness of two or more measurements to each other. Precision is how often you can repeat the same measurement, regardless of a targeted value.
The closeness of a measured value to a standard or targeted value. Accuracy is the ability to closely hit a targeted value.
High quality metering pumps are precise when they arrive from the factory. Pressures, temperatures, viscosities, and other factors will not affect the ability of a quality metering pump to be precise. In other words, these factors will not affect the pump’s ability to produce the same output repeatedly for a long time. A quality metering pump’s output should not fluctuate while in operation.
However, those same factors do affect a metering pump’s resulting flow rate, or, a metering pump’s accuracy. For example, at an operating pressure of 50 psi let’s say a metering pump is metering 5 gallons of a chemical in an hour. If this same application had to operate at a pressure of 150 psi, the flow rate will drop slightly to something like 4.5 gallons of chemical in an hour. A small amount, but with applications that call for extreme accuracy, not knowing you lost 0.5 gallons in an hour can make all the difference in the world.
This article is focused on helping the pump operator to reach their exact
desired output. Once achieved, a quality metering pump, like Madden’s diaphragm metering pump line, will repeat that targeted output, with an accuracy of +/- 1% for years of dependable service life.
So why the need for such precision and accuracy? Many other pumps have controllable outputs.
There are several reasons why one would need a liquid/chemical pumped with precision and accuracy of +/- 1% via a metering pump, rather than settling for a centrifugal pump with controls for the output (as an alternative example).
- Errors in production: You will want repeatable +/- 1% accuracy when the application calls for the dosing of a liquid/chemical to produce a different liquid or chemical. If a pump outputs too much or too little, the resulting solution will not serve its purpose.
- Wasting money via your product: In this scenario adding too much of a liquid or chemical to a process may not harm the resulting solution, but it is a waste of the liquid/chemical nonetheless. And if your pump is running 24/7/365, pumping too much of a liquid/chemical will hurt your bottom line. Wasting chemicals is expensive, and can be harmful to the environment.
- Wasting money via your time: trying to design a centrifugal pump to act as a dosing pump will take a lot of time from an engineer to come up with the right instrumentation to do the job. You will either need to spend thousands of dollars to automate the system, or an operator will need to constantly monitor and adjust the pump. With a metering pump, once you have it running at the flow rate you need, you can walk away and be confident it will dose the specific amount needed.
Understanding Madden metering pumps, and how to ensure +/- 1% accuracy
Madden has 3 different series of diaphragm metering pumps, the JN series, MF series, and MH series. Among our 3 series of pumps are many different models with different minimum and maximum output capacities. Let’s walk through an example of how and why you need to calibrate a Madden metering pump to achieve and exact output with +/- 1% accuracy.
For this example, let’s use a Madden MF160C which has a flow rate range of 6-60 GPH and is rated for up to 160 psi operations. Let’s understand what all can cause the actual rate for this Madden MF160C to vary by a max of a few gallons per hour. These factors include:
- The system’s back pressure being well above or below 100 psi (every Madden pump is tested at 100 psi before they leave the shop to ensure it reaches the model’s rated output and has no leaks or other defects)
- The pump is or is not set up with a flooded suction. And vice versa, any suction lift the pump must overcome will affect total output.
- The systems’ total feet of piping to the point of metering is extensive
- There are many turns in the piping, causing more drag/friction
- Pipe size is significantly bigger or smaller than the pump’s inlet and outlet sizes
So as you can see, there are many factors that play a part in the actual output of a metering pump, but remember all of these factors are only going to affect the pump’s output by a few gallons per hour at the most.
The importance of all of this information is to help you, the end user, understand the need to calibrate your metering pump to know exactly
what you’re getting in output. Sticking with our MF160C example, let’s say you wanted to pump at 30 GPH. It isn’t as simple as turning down the manual adjustment knob to 50%. Turning the manual adjustment knob down to 50% on a MF160C may get you 29.1 GPH or 29.5 GPH, it is dependent on pumping conditions. If you need 30.0 GPH exactly, then it’s time to calibrate.
So how do you ensure your Madden pump is pumping exactly what you need it to pump?
The two easiest and best ways to ensure your Madden pump is giving you an accurate and precise output is to calibrate it using either calibration columns or a flow meter with a rate and totalizer.
And Madden has you covered on both.
Madden’s standard line of Griffco PVC calibration columns can handle any flow rate of a Madden metering pump. The units are listed below
To use a Griffco calibration column is fairly easy and extremely accurate. You will need to purchase two isolating valves to be used at the top and bottom ends of the calibration column. The top of the cylinder should be vented back to the storage tank or to drain. To begin, fill the cylinder to the top mark then close the valve from the chemical tank. Switch on your Madden metering pump and draw down the chemical in the cylinder for 60 seconds. Switch the pump off. Use the number of mL or CC’s that has been pumped out of the cylinder to find your Madden pump’s current flow rate by dividing by 3,785 and then multiplying that number by 60. Here’s a couple of examples on the uses of a calibration column (continuing with an MF160C):
Example 1, fine tuning for exact output:
Here we have filled a Griffco calibration column to the top and our Madden MF160C’s manual stroke adjustment knob turned to 100% which is “100” on the dial scale. We then turn on and pump for 1 minute after which we note that 3,887 mL have emptied from the calibration column. If we divide 3,887 by 3,785 we get 1.027, and this multiplied by 60 brings us to 61.62 gallons per hour. So in this example our Madden MF160C is pumping 1.62 gallons more than its rated max capacity (likely due to low operating pressures).
The next step would be to back off the manual stroke length adjustment knob slightly and repeat the processes until you are at exactly 60 GPH, if this is the output you desire.
Example 2, performing multiple runs to develop your pump’s curve:
in this scenario we start the same way as we did in example 1. After we have recorded our rate when the manual stroke length adjustment knob of our pump was at 100%, which again, is “100” on the dial scale, we should run the test at least 3 more times. Madden manufacturing suggests using “75” on the dial scale, “50” on the dial scale, and then “25” on the dial scale for the next 3 runs.
Using these 4 recorded outputs will allow you to draw an output curve for your pump in its current application. This will allow you to know how much your Madden metering pump will pump at nearly any number on the manual stroke length adjustment knob dial without having to use the calibration column every time you make an adjustment.
Madden also offers Seametrics flow meters for end users. There are a wide variety of flow meters to meet nearly any flow rate and chemical resistance need. Contact the factory for options and pricing.
If you don’t see something you like here, contact us to find out what more we can offer. If you have an inquiry for any products that compliment a Madden Diaphragm metering pump, we will look into procuring that for you.
If you have an application that needs precise and accurate metering, consider a Madden Diaphragm Metering pump. Consistency and durability are the focus of our chemical metering pumps and we have the instruments to make your pumping capacities exactly what you need them to be.
Call (574) 295-4292 or email: email@example.com to place an inquiry. We’d love to help you find the right solution for your application!