Even if pipes are connected to the pump suction and discharge nozzles without transmitting any stresses or strains, there are still forces and moments in the piping, known as pump nozzle loads, which have to be taken into account depending on the prevailing operating conditions (pressure, temperature). These can lead to stresses and deformation of the pump casing and to coupling misalignment (see Coupling alignment) which affect the smooth running of the centrifugal pump and compromise the service life of the flexible elements in the shaft couplings. The permissible pump nozzle loads are therefore limited.
As the load profile for each pump nozzle is composed of three force and moment components each, it is impossible to specify all conceivable combinations for the theoretical limits of pump nozzle loads. Two options are therefore available: performing calculations to verify whether the specified system-side nozzle loads are permissible, or applying greatly reduced limits suitable for any application. These limits are stipulated in various technical codes, e. g. in the EUROPUMP guidelines on Permissible Forces and Moments on Centrifugal Pump Flanges (1986) which apply to several pump types, or in the API STD 610 and ISO 5199 standards for single-stage chemical and refinery pumps). See Fig. 1 Pump nozzle load
The example of a single-stage volute casing pump described in the EUROPUMP guidelines demonstrates the difference between installation of the pump on a baseplate grouted with a grouting compound or concrete (solid lines) and installation of the pump on a baseplate which is not grouted (dashed lines). The permissible moments (Tmax = orange lines) in the flange plane and the permissible forces (FH, max in x, z plane and FV, max in y direction) to ISO 5199 apply to single-stage volute casing pumps made of ferritic steel or nodular cast iron to DIN 24256/ ISO 2858 at room temperature.
Lower values apply to austenitic cast steel or lamellar graphite cast iron, or for higher temperatures.