Summary
- What is a pulsation dampener used for?
- Why a Bigger Dampener Is Not a Better Dampener
- The Role of the Pulsation Dampener in API 618
- Our Method: Sizing, Simulating, Verifying
What is a pulsation dampener used for?
The pulsation dampener attenuates pressure pulsations generated by the compressor before they reach the piping lines. Due to its position, it constitutes the first level of damping in the network.
A reciprocating compressor intermittently draws in and discharges gas. This chopped flow creates pulsations: periodic pressure fluctuations at the machine’s rotational frequency and its harmonics. Transmitted to the piping, they become dynamic forces, then vibrations, with a risk of fatigue on nozzles, flanges, and supports.
Mounted as close as possible to the cylinder flanges, the dampener (also referred to as a pulsation bottle) attenuates these fluctuations thanks to its volume. Equipped with internals (baffles, choke tube), it behaves like a low-pass acoustic filter: it allows the average flow to pass and attenuates pulsatile components beyond its cutoff frequency.
Why a Bigger Dampener Is Not a Better Dampener
A larger volume does not automatically improve attenuation. Beyond specific requirements, it adds acoustic, mechanical, and financial risks.
Poorly placed acoustic resonances. The dampener has its own resonance frequencies, linked to its dimensions and the speed of sound in the gas. If these coincide with the compressor’s harmonics, they amplify pulsations or transfer them to the network, where they become difficult to control.
Degraded mechanical behavior. The dampener is supported by the cylinder. A heavier dampener lowers the natural frequencies of the cylinder-dampener assembly and brings them closer to the machine’s excitation frequencies.
Bulk, overweight, additional cost. A larger pressure vessel weighs more, takes up more space on the skid, and costs more, without demonstrated gain in pulsation control.
The objective is therefore not the largest volume, but the volume adapted to the frequencies involved and the downstream network.
The Role of the Pulsation Dampener in API 618
The sizing of dampeners is the first step in the pulsation study described by API 618. It is then verified with the piping network, according to the chosen study level.
The API 618 is the American Petroleum Institute standard for reciprocating compressors in the petroleum, chemical, and gas industries. It defines three design approaches, or Design Approaches:
- DA1: The pulsation dampener is designed using an analytical method to meet in-line pulsation levels and allowable pressure drops;
- DA2: Acoustic simulation of the compressor, dampeners, and piping lines, supplemented by a support review based on an analytical method and experience;
- DA3: The same acoustic simulation as in DA2, supplemented by a mechanical response study using modal analysis.
A planning constraint weighs on the process: dampeners are pressure vessels with long lead times. Their sizing is therefore often finalized upstream, before the piping layout is determined. Hence the importance of subsequently verifying their behavior with the actual network: it is at this stage that a resonance is corrected on paper, not on site.
Our Method: Sizing, Simulating, Verifying
At SIM Engineering, we size the dampener and then verify its behavior within the complete system, up to commissioning if necessary.
- Input data: compressor characteristics and service conditions, gas properties, isometrics, and support.
- Sizing of the dampener and its internals by acoustic simulation, even when DA1 level only requires an analytical method, taking into account your space and lead time constraints.
- Acoustic simulation of the complete system (compressor, dampeners, and piping) over the operating range, to locate the actual network resonances.
- Mechanical verification: support review, flexibility study, and, in DA3, mechanical response by modal analysis.
- Prioritized recommendations: adjustment of volume or internals, orifice plates, modification of support.
- On-site measurements of pulsations and piping vibrations during commissioning, to validate the actual behavior of the installation.
As an independent engineering firm, we have no equipment to sell: each recommendation aims for sizing to specific requirements. For details of our services, consult our page API 618 study of reciprocating compressors. On the choice of validation measurements, also read acoustic and vibratory measurements: what are the differences.
Pulsation Dampener: Key Takeaways
The pulsation dampener is not just a buffer volume: it is the first filter in the network, and its sizing determines the rest of the pulsation study. The right dampener is one that complies with API 618 with the correct volume, mass, and cost. Do you have a dampener to size or verify? Discuss with a SIM Engineering engineer from the design stage: it is at this stage that each adjustment costs the least. Contact Us