What is the PFA Module?

(PFA Module Only) Steady state pressure and flow dynamics, henceforth referred to simply as “pulsation”, is a common problem in PD pump systems, which can cause high vibration, fatigue failures, frequent maintenance outages, and flow uniformity or product quality problems.

The PFA module helps engineers identify and avoid resonant frequencies in systems, especially in those caused by positive displacement pumps. Problems can arise when the frequencies that are excited by pulsation are at or near the acoustic resonant frequencies of a fluid system. The module is used to calculate the acoustic resonance frequencies that could damage system equipment.

How Does the PFA Module Work?

The Pulsation Frequency Analysis (PFA) module is used to determine resonant frequencies that could damage system equipment by calculating the acoustic resonance.

The general steps of pulsation analysis involve the following:

1. The piping and process equipment system is first modeled.

2. A pulse is generated to determine excitation frequencies, then a Low Pass Filter is applied to the pulse in order to determine the forcing function. This forcing function is then placed in the transient data of the junction at which the pulse is applied.

3. The model is run with the forcing function to generate the Excitation Frequency Analysis graph, and the user selects frequencies for analysis from the graph. If the pulsation source is specified to be a PD pump, the PFA module calculates the PD pump speeds (RPM) that will excite the chosen frequencies, and a table of PD pump speeds that abide by the specifications in the Pulsation Setup group in Analysis Setup will be populated.

4. The pump speeds of interest to be analyzed are selected by the user, and the PFA module automatically generates read-only child scenarios that model the pump operating at the selected speeds.

5. The system can be modified accordingly and reanalyzed if desired.

The PFA module will also provide a warning in the Output if the maximum peak-to-peak pressure limit has been exceeded at any location in the system, according to the API 674 standardAmerican Petroleum Institute. 2010. API Standard 674 with Errata (May 2014) 3rd Edition. Positive Displacement Pumps-Reciprocating. Annex C, sections A.1 and A.2, pages 67-68 .

Using the PFA Module

The user has the option of activating or not activating the PFA module when AFT Impulse first loads. After AFT Impulse is loaded, the PFA module can be activated or deactivated for use from the Modules panel in the Analysis Setup window or the Tools menu. Whether or not PFA is activated impacts the Analysis Setup window, Analysis menu, Output window, and Graph Results window as discussed in the Modules panel topic.

If the PFA module is active, the user can still run models without pulsation. This is selected under Pulsation Frequency Analysis on the Analysis menu. Hence there are three possibilities for the PFA module.

• PFA is not active

• PFA is active and pulsation is disabled

• PFA is active and pulsation frequency analysis is performed