scope:

This document covers rotodynamic pumps, as referenced in the Hydraulic Institute Standards.

(Note: Figures 9.6.8.1.2a, 9.6.8.1.2b, and 9.6.8.1.2c are provided to facilitate the use of this document. For more information on pump types, refer to ANSI/HI 14.1-14.2 Rotodynamic Pumps for Nomenclature and Definitions.

Evaluation scenarios include the following:

• New equipment design and manufacture prior to field installation

• Existing equipment condition assessment in the field

• Existing equipment undergoing field modification

• Existing equipment undergoing field rerate

• Dynamic problem field troubleshooting

Evaluations may include drive systems, ancillary equipment, and the effects of local foundation and piping systems, as appropriate.

Rotodynamic pump dynamic response is the result of excitation forces sourced in the pump or its system, amplified or attenuated by natural frequency resonances (poles) or antiresonances (zeros), as well as by how well the pump is supported by its foundation. The influence and control of the excitation forces, natural frequencies, and foundation support will all be considered in this guideline.

Determination of pumping equipment natural frequencies is important because if a natural frequency is numerically close to an operating speed or other excitation frequency, a state of resonance could exist wherein a response to an excitation force can be greatly amplified, with the resulting stresses and deflections possibly causing premature equipment failure.

Typical excitation forces can be described in terms of the resulting amplitude at a given discrete frequency (e.g., vane passing frequency) or a frequency span, and can be associated with either mechanical or hydraulic causes. Both mechanical and hydraulic excitations are within the scope of this standard, in terms of prediction as well as effects, with certain limitations (discussed later in this section).

This document provides guidelines related to the topic of dynamics of pumping machinery.

To provide practical guidance useful across a broad range of types, sizes, and applications of pumping machinery, three levels of analysis, categorized by methodology, are discussed:

1) Simple calculations that may be performed using a hand calculator using first-order equations.

2) Methods employing basic mass elastic modeling using commercially available software tools, such as finite element analysis (FEA) programs.

3) Computational methods involving multiple specialty programs and complex methodologies.

For each level:

• Terms are defined

• Guidelines are provided concerning when a certain analysis level should be applied

• Guidelines are provided concerning when a certain analysis level should not be applied or trusted

• Limitations are presented concerning the various analysis methodologies

• Recommendations are made about what should be done (although not necessarily all the details regarding how to do it) and what each analysis comprises

• Suggestions are provided concerning what equipment or components should be analyzed

• Lists are provided of typical design and technical information needed to perform the analysis

• An appendix is provided with a sample specification

• A checklist of information is suggested for inclusion in the analysis for reviewing purposes

• Recommendations are made for verification methods that may be utilized, where applicable

• Recommendations are made for minimum standards to be applied concerning numerical analysis, such as FEA, as a function of analysis level

• Suggestions are made concerning how the analysis would fit into the timetable of a project and how it would interface with the other tasks to be performed within the entire scope of the work to be accomplished

The following analyses are beyond the scope of this document:

• Analyses involving complex time-dependent excitation due to fluid phenomenon or external sources of vibration.

• Seismic analysis considerations involving the motion of the mounting base of a structure, e.g., as in an earthquake.

• Analyses involving certain considerations of hydraulic excitations, such as:

- Acoustic/pressure pulsation analysis (e.g., acoustic resonance of the piping system or network)

- Analyses involving computational fluid dynamics (CFD) methods, such as

ο Conducting rotor or structure fluid interaction calculations as a function of flow

ο Quantifying the effect of vortex shedding on a vertical pump casing

• Determining the effect on rotor excitation of pressure pulsations generated by an impeller vane passing a volute tongue.

• Rotor stability analysis is outside the scope of the analyses conducted as standard procedure as presented in this document due to the limited exposure of most pumps to rotor-stability-related issues. With respect to this document, a rotor stability analysis may be considered as an optional analysis. A rotor-stability analysis may be advisable in applications involving boiler feed pumps, charge pumps, high-energy density pumps, and very high-speed pumps. For information regarding stability analysis, refer to American Petroleum Institute (API) RP684.

Vibration level shop and field acceptance criteria based on test results are excluded from this guideline. Refer to ANSI/HI 9.6.4 Rotodynamic Pumps for Vibration Measurements and Allowable Values.