To see the basic principle of a tubing pump in action, lay a soft rubber or plastic tube across a hard, flat surface. (See Diagram Below) With a rolling pin, pinch the tube closed at the line A-A, then roll the rolling pin toward the line B-B. As the rolling pin is pushed forward, any fluid (liquid or gas) is pushed along in front of it. Behind the rolling pin, the tube springs back into its original shape, which creates a vacuum; atmospheric pressure pushes the fluid in to fill the vacuum. As the rolling pin approaches line B-B, start a second rolling pin at A-A. This will allow the pump to stay in operation when the first rolling pin is removed.
By placing the tubing in a "U" shape slightly larger than 180°, you can use two rollers to seal the tube against a rigid, concentric housing of slightly more than 180°. As the first roller goes around, the fluid in front of it gets pushed out. As the tube springs back, atmospheric pressure pushes more fluid into the tube. Before the first roller leaves the sealed condition, the second roller starts to squeeze the tubing tight. Now you have a rotary pump.
Since the pump is a rolling valve that is always closed, what occurs on the suction side of the pump has no influence on what occurs on the discharge side of the pump, and vice versa. Clearly, a tubing pump cannot be any better than the tubing it employs. If the tubing has a maximum pressure limitation of of 40 psi, that is the pressure limit for the pump in which it is used. The ability of the tube to rebound under various conditions will determine its suction lift. If, for example, the tubing comes back to shape to draw a near-perfect vacuum, the pump will be self-priming to 33 feet at sea-level. Conversely, if the tubing cannot come back to shape at a suction lift of 15 feet with water, that is the pump's limit.
Abrading of the tubing is not crucial, particularly if the tubing is lubricated with silicone grease or some other lubricant. Tubing life depends upon how well the compound withstands repeated flexing. Since the number of rollers in a pump determines the number of flexes per revolution, it is best to keep the number of rollers at a minimum. One roller would be ideal, except that the mechanical configuration makes it expensive to build and cumbersome to change the tubing, so two rollers becomes the optimum for long life. More than two rollers simply means that you flex the tubing more per revolution. The only advantage of the multi-roller pump is the ability to use less precision in the manufacture because you have more than one roller squeezing the tube all the time.
The constant kneading of the rollers against the tubing causes the tubing to heat up. Generally, if pump speeds exceed 200 rpm, the tubing becomes heated to a point at which it tends to fail rapidly. TAT supplies its own speed-reducing gear train as part of nearly every pump it sells -- and delivers greatly increased tubing life.
So, call us toll free at 1-800-243-2526
Take advantage of our over 25 years of experience designing, building and applying tubing pumps. We will be happy to help you choose the best one for your application. We will also tell you what else you should look at if yours happens to be an application for which a tubing pump is not the best solution.
Remember, a tubing pump is self-priming, pumps abrasives, runs dry without harm, handles viscous material, pumps without shear and pumps sterile solutions. It can operate with a blocked suction, but cannot operate against a blocked discharge.