11 Determine critical fan speed, NM at a specified engine speed, NE (RPM). 2. Determine fan power, HP, or torque, TM required at the critical speed. (HP or ft-lbs) Convert power to torque, if necessary. M M N lbs HP T ft 5252 ) ( Determine fan system operating pressure, P at the critical speed. (PSI) This pressure is up to the designer’s discretion and depends on several factors including pressure ratings for system components, component sizes and system life requirements. Pump and motor sizes will be smaller with higher pressures but system life reduces as pressure increases. Also, any “under hood” regulations should be considered. Calculate motor displacement. P D c TM M 1374 ( ) Calculate flow required, QM for the motor at critical speed. 3485 ) ( M M M Q GPM D N If a clipping relief valve is not being used in the motor, required pump flow, QP = QM - Skip to step 8. Determine additional flow, QA, to allow over the relief valve to compensate for temperature variations and component wear for maintaining a consistent fan speed (at critical fan speed NM). Add this to the required motor flow, QM to get the flow required from the pump. QP A M P Q GPM Q Q ) ( This flow is up to the designer’s discretion. It is safe to assume a 10% reduction in system volumetric efficiency over its life. Also, it is safe to assume a 5-10% reduction in volumetric efficiency at oil temperatures exceeding 180°F. In order to compensate for these factors, the pump can be sized for additional flow. Note: This additional flow will be discharged over the relief valve at system pressure. This should be calculated into the total heat load requirements of the system. Determine pump speed, NP at the specified engine speed, NE (RPM). This is determined from the engine to pump speed ratio. Example: If the ratio of engine speed to pump speed is 1:1.2, 1.2 E P N N Calculate pump displacement. P P P N D c Q 4030 ( ) Calculate required maximum input torque, TP for the pump. 68 ) ( P P lbs P D T ft This is required for selecting the type of shaft end (i.e. 9 tooth vs. 11 tooth spline, etc.) and provides for engine HP loss to drive fan at maximum condition. 11. Select the proper pump and motor series based on displacements, pressure, shaft loading, mounting requirements, etc. from the Concentric pump and fluid motor families. See catalog page 14 to begin family selection. Note: The pump and motor efficiencies assumed in the equations above are conservative to insure that the system is not under cooled. Variables: NM Motor Speed (RPM) QM Motor Input Flow (GPM) DP Pump Displacement (cc) NP Pump Speed (RPM) QP Pump Output Flow (GPM) DM Motor Displacement (cc) NE Engine Speed (RPM) TM Motor Output Torque (ft-lbs) P Fan System Pressure (PSI) HP Fan Power (HP) TP Pump Input Torque (ft-lbs) QA Additional Flow over RV (GPM) See Application Data Sheets on pages 12 & 13. Step by Step instructions on how to apply a Fan Drive System. The balance of the fan drive information is to be filled in on the Fan Drive Application Data sheets (see pages 12 and 13). NOTE: Formula numbers in bold and circled correspond to numbers in bold and circled in Application Data Sheets on pages 12 and 13. HowTo Apply A Fan Drive System 1 10 9 8 7 6 5 4 3 1115 quality products for mechanical & fluid power jbj Techniques Limited, www.jbj.co.uk quality products for mechanical & fluid power ~ jbj Techniques Limited, www.jbj.co.uk UK distributor for Concentric Hydraulics
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