Hy~Line and Ultima Lobe Pumps - Jabsco - #4

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Separate .timing. gears exactly synchronise the rotation of the two shafts to ensure that the pump head components do not touch, unlike for example gear pumps where one gear drives the other and can wear, resulting in a loss of efficiency. The clearances within the pump head must be large enough to allow for shaft deflection under pressure and for thermal expansion without rotor contact but must also be kept as small as possible to maintain pump efficiency. Volumetric efficiency is lost when liquid .slips. from the discharge side back to the inlet side through the rotor clearances. The amount of slip is affected by the size of the clearances, the differential pressure generated by the pump and the fluid viscosity: Larger clearances result in higher slip; the fluid can more easily leak back through the larger area (Fig 5). Higher pressure results in higher slip; the pressure forces more liquid back through the clearances (Fig 6). Higher fluid viscosity results in lower slip; high-viscosity liquids flow less easily through the pump head clearances than thin liquids (Fig 7). Therefore, especially when pumping thinner liquids, rotor clearances are kept as small as possible to maintain efficiency. However, higher pressures force the rotors sideways within the rotor case, towards the inlet port, also slightly tilting the rotors. Therefore for higher pressures, more clearance is necessary to prevent rotor to rotor case contact, up to a maximum allowable for a particular shaft and rotor configuration. Lastly, high operating temperatures and, especially, sudden changes in temperature e.g. during CIP result in different rates of expansion of the pump head components. Therefore sufficient clearance must be provided to allow for this. From the above, it can clearly be seen that the output flow rate from a Lobe Pump is a function of: . Rotor diameter . Rotor length . Speed of rotation . Lost flow due to slip back through internal clearances The speed at which the pump runs is calculated to displace the required flow, plus extra displacement to compensate for any slip. 2/00 5.20 Hy~Line and Ultima Lobe Pumps USA UK GERMANY Jabsco Jabsco Jabsco GmbH 1485 Dale Way Bingley Road Oststrasse 28 Costa Mesa Hoddesdon 22844 Norderstedt CA 92628-2158 Hertfordshire, EN11 0BU Tel : +1 714 545 8251 Tel : +44 (0) 1992 450 145 Tel : +49 (0) 40 53 53 73 0 Fax : +1 714 957 0609 Fax : +44 (0) 1992 467 132 Fax : +49 (0) 40 53 53 73 11 Warranty: All products of the company are sold and all services of the company are offered subject to the company.s warranty and terms and conditions of sale, copies of which will be furnished upon request. The information provided herein is for guidance only, it does not constitute a guarantee of the performance or specification of any individual product or component. ©Copyright 2000 ITT Industries - Jabsco 43010-0172 Volumetric Efficiency Pump Output Fig 4 Fig 5 Fig 6 Fig 7