Hy~Line and Ultima Lobe Pumps - Jabsco - #3

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Jabsco Hy~Line and Ultima positive displacement rotary Lobe Pumps are designed to pump delicate, viscous and particle-laden fluids as well as thin liquids which require an all stainless steel pump. The design of Jabsco Lobe Pumps is influenced by some fundamental engineering principles and it is useful to understand these first to ensure their most effective selection and operation. All Hy~Line and Ultima Lobe Pumps use the same principle of operation. Two rotors turn in opposite directions; fluid enters the pump from the inlet port and fills the space between the rotors. This fluid is carried around the outside of the rotors and is forced out of the discharge port as the rotor lobes mesh together - see Fig 1. The displaced flow rate of the pump is therefore directly proportional to the diameter of the rotors and the speed at which the pump rotates. In Jabsco Lobe Pumps, each rotor is supported on its own shaft and there are no bearings inside the pump chamber, so all forces from the fluid pressure are transmitted through the shafts to external bearings. The rotors are therefore overhung, as the shafts are cantilevered (see Fig 2) and are designed to resist the fluid pressure without excessive bending. The bearings are permanently lubricated and are sealed from the pump head ensuring that: . No lubricant contaminates the pumped fluid . No bearing material is worn away . No pumped fluid (which may be corrosive or abrasive) can enter the bearings . No pumped fluid is trapped behind bearings from where it cannot be cleaned out Being a positive displacement pump, flow is related not only to the rotor diameter but also the rotor length. A rotor length increased by 50% will displace 50% more flow. The longer rotor also has a larger surface area on which the fluid pressure acts trying to force the rotor to one side (see Fig 3). Therefore longer rotors put more load on the pump shafts and bearings at any particular pressure, so the maximum working pressure of a pump using a long rotor is lower than that of a short rotor, limited by the clearances provided and Ultimately by the shaft strength. When the pump is running within its operating limits, the rotors never touch each other and never touch the case in which they rotate. Fig 4 overleaf, shows the areas where small clearances are provided: between the two rotors (a), at the tips of the rotors (b) and on the front and rear faces (c). These clearances are typically only 0.05 to 0.25mm (0.002 to 0.010 inches). This absence of contact ensures that no material contaminates the pumped fluid and also makes Jabsco lobe pumps ideal for abrasive fluids. Hy~Line and Ultima Lobe Pumps Overhung Rotors Basic Principles of Design and Operation Fig 1 2/00 5.19 Rotor Lengths Rotor Clearances Fig 2 Fig 3