Flow Metering and Flow Control with Multi-channel Peristaltic Pumps

Flow Metering and Flow Control with Multi-channel Peristaltic Pumps
Accustaltic Metering Pumps combine both flow control and flow metering into one device. Create accurate, metered, parallel flows with difficult or multiphase fluids. Ideal for all fluids, and especially suited for slurries, thick and chunky materiasl and rugged environment applications. The accustaltic pump is highly accurate and repeatable. There are no delicate parts, fins, or bearings to be fouled by the metered fluid. Many types of pump tubing are available provide the perfect combination of performance and chemical resistance.
Using the pump as a flowmeter: The accustaltic pump is positive-displacement pump, meaning that each turn pumps the same amount of liquid. this means that by simply counting the number of turns, you can know exactly how much fluid you are pumping. This can be by a hall-effect or reed switch on the shaft, or by a rotary encoder. You can see both at right and below the simple shaft sensor that tells the rate controller or PLC exactly how fast the pump is turning. Brackets and mounts are available for many common speed sensors.
	Great for: Continuous flow industrial processes metered dosing Viscous, abrasive, corrosive, caustic and shear sensitive materials Dividing one flow into multiple metered flows Lubricant pumping Glue pumping Very large flows (to 40 GPM), where the pulse of a hose pump is undesirable. Pressures to 60 psi and higher(4 bar)	Use Accu-Staltic™ metering pumps anywhere you use: liquid flow meters, especially parallel flows flow measurement positive displacement flow meters multiphase flowmeters flow rate meters fluid flow meters multichannel fluid flowmeters ball flow monitors
Tubing displacement and flow curve linearity: The tubing displacement is how much fluid is pumped with one full revolution of the pump. For the pump to have a linear flow rate, this displacement must remain constant over the speed range of the pump. In an Accu-Staltic pump, displacement changes very little with speed or time when properly installed. Below is an actual evaluation using Norprene 3/8" ID tubing. Curves will vary slightly with the type and size of the tubing you choose.
			Positive Displacement means uniform flow The flatness of the curves at left shows the uniformity of the pump as a flowmeter over the various speeds. Note that under higher inlet manifold pressures (blue line at left), the soft Norprene has an increase in displacement, as the tube stretches. Stiffer tubes such as Suprene, Prothane, and Santoprene will be less affected by this phenomena.
			In Chart 2, we see the flow rate of tubing after a significant period of run time- 100 hours. It has lost about 4% of its original displacement as it has worn-in, but the curves are still basically flat. If better accuracy is required, a minor calibration adjustment to reflect the current displacement would restore very high accuracy of the pump as a flowmeter.
Linear Flow Rate: A good metering pump has a linear flow rate: ie: when the speed of the pump doubles, the flow doubles. You can see in the graphs below, how the flow rate of a typical configuration remains linear. The more linear the flow rate, the more accurate your application.
			In the chart at left, you see that doubling speed doubles flow, with only minor variations due to vacuum or pressure on the inlet.
			In the table at left, you can see that even after 100 hours of pumping, the flow rate per second is nearly unchanged. It is interesting to note the slight loss of linearity when the pump is required to lift (pull vacuum) as shown in the green line. The effect really only becomes significant at very high pump RPMs. This is due to wearing and loss of elasticity in the rubber compounds over time and is normal. Flooding the pump inlet, and keeping to lower pump speeds can pretty much keep this phenomena under control. In cases where the inlet must lift, or higher accuracy and wide speed ranges are required, choosing other, more elastic hose polymers such as Prothane II, will maximize the pump's linearity.
Accuracy limits: A peristaltic pump is only as good as its tubing. The manufacturing tolerance of most Commercially available tubing will give a plus or minus 2-3 % variation in internal diameter between tubes. Some tubing is manufactured to tighter tolerances, and this can help when accuracy is particularly critical. The tubing will also vary some with ambient temperature and with wear as it gets older. Generally, you should be able to maintain flow rates of plus or minus 5% of the average of all the tubes. If you are using the pump over a narrow speed range, you will see much better accuracy than this. The Chart below at right shows typical variation in flow between pumping channels. If your application requires tighter accuracy than plus or minus 5% overall, that can usually be achieved. Please call to discuss your application and we can discuss this further.
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