| A Masterflex pump produces a pulsating flow because of its pumping action. As fluid enters the pump head, it is trapped between two rollers in a ‘pillow’. This pillow of fluid is dispensed at the outlet, and there is a brief pause in flow until the next pillow of fluid is pushed through the pump head to the outlet. Since there are three rollers in the Masterflex design, there are three pulses of fluid dispensed with each revolution of the motor. In some applications, it is desirable to reduce the pulsation of the flow as much as possible. In such cases, follow these guides: 1. Use a pulse dampener A pulse dampener is simply a retaining vessel. It works because air is much more compressible than fluid. Pulsating flow enters the vessel, an air pocket trapped above the liquid absorbs the pulses and a smooth flow exits the pulse dampener. Cole-Parmer® offers an inexpensive pulse dampener (HV-07596-20) for L/S size tubing; or you can easily make your own pulse dampener for larger sizes of tubing using a retaining vessel and appropriately sized fittings. The outlet should be located even with or lower than the inlet and both should be located near the bottom of the container to reduce the dead volume of the system. The disadvantages of using a pulse dampener are increased dead volume and the flow does not stop immediately when the pump is turned off. A pulse dampener can suppress as much as 90% of the existing pulsation. 2. Use an adjustable occlusion pump. Reducing the occlusion (the amount the tubing is being squeezed) decreases the degree of pulsation. This is because there is less of a distinction between pillows of fluid. The diagram below (Figure A) illustrates this point. Adding back pressure will further decrease pulsation, however adding back pressure will decrease accuracy and flow rate since the fluid will slip backwards through the pump head. Minimum occlusion will reduce pulsation to approximately 75%. 3. Use dual heads with offset rollers. In this case, two pump heads with rotors offset 30° are coupled together, the inlet tubing is split into 2 channels using a y-connector and then the 2 channels are rejoined at the outlet. The geometry of the rollers results in the pillow from one channel overlapping with the pause in flow of the second channel. The overlapping of the waves results in a flow with about 95% less pulsation. See Figure B. 4. Add discharge tubing. The tubing will absorb the pulsation, especially softer tubing such as silicone or C-FLEX®. Longer discharge tubing will also increase the back pressure due to frictional forces. This tends to compress the pulsations together. This will decrease pulsation up to 60%. |