2013-08 / 04 Catalogue LM1 - 008 UK Page 5 Edition Example of the calculation of a comressed- air reservoir volume for the emergency drive In our exemplary calculation, a DMO 15/15 is used wich according to operators information needs approx. 5 to 8 minutes to move for example a lance out of the melting furnace. For this period of time, a sufficiently large compressed- air reservoir is to be provided which would drive the air motor in case of main drive failure. The motor runs at a speed of n = 1500 min-1 and is to be operated at 6 bar. The max. storage pressure was specified to be pmax = 10 bar. The calculation of the requiered storage volume must always be based on the absolute air consumption. Technical data: motor : DMO15/15 nominal speed : n = 1500 min-1 idle speed : n = 1680 min-1 (speed used as calculation basic) air consumption (catalogue p.11) : Q ~ 20,5Nm3 / min operating pressure : pcont. = 6 bar duration of the travelling path : t = 5 bis 8 minutes max. storage pressure : pmax = 10 bar applicable pressure difference : pexis. = 4 bar (pmax - pcont.) The required compressed- air storage volume is calculated exclusively on the foundation of the applicable pressure difference. Calculation: 20,5 Nm3 / min . 8 min = 164 Nm3 164 Nm3 / 4 bar = 41 m3 storage volume The storage volume must be o less than 41 m3 to ensure that it will still have a pressure of 6 bar after withdrawal of 164 Nm3 by way of reduction to 6 bar via pressure- reduction valve. Furthermore, take into consideration that the pressure- reduction valve may allow passage of a slightly higher pressure so that the 164 Nm3 are withdrawn faster than calculated. Accordingly, it is necessary to provide a sufficiently large reserve volume. V = Q . t _____ pexis.
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