Pulsation suppression vessels — commonly called bottles — are the primary tool for controlling pulsation in reciprocating compressor systems. Understanding how they work, and more importantly how they can fail to work, is essential for anyone specifying or reviewing a compressor package.
The Basic Principle
A pulsation bottle is essentially an acoustic filter. Its large volume relative to the connecting pipe creates a volume-choke-volume acoustic filter that attenuates pulsation energy at specific frequencies. The larger the bottle volume relative to the cylinder displacement, the greater the attenuation.
The key sizing parameter is the acoustic filter cutoff frequency. The bottle is designed so that its cutoff frequency falls below the fundamental excitation frequency of the compressor — typically the running speed in Hz multiplied by the number of cylinders. Pulsations above the cutoff frequency are attenuated; pulsations below it pass through.
How Bottles Fail
There are three primary failure modes for pulsation bottles. First, undersizing: if the bottle volume is insufficient, the cutoff frequency rises above the fundamental compressor excitation frequency and the bottle provides little useful attenuation. This is the most common sizing error and is entirely preventable with proper acoustic simulation.
Second, acoustic resonance within the bottle itself: bottles are not perfectly behaved acoustic filters. They have internal resonance modes of their own, and if these modes align with compressor excitation frequencies, the bottle can actually amplify pulsations at those frequencies rather than attenuate them.
Third, internal baffles that are incorrectly sized or positioned. Internal baffles control the acoustic path length within the bottle and directly affect the resonance modes. A bottle with poorly designed baffles may pass a volume check but fail to perform as intended.
API 618 Verification
API 618 DA2 and DA3 analyses both verify bottle performance by simulating the full acoustic system and comparing pulsation levels at critical locations to the API 618 pressure drop allowable. This is the correct way to verify bottle sizing — not by rule-of-thumb volume calculations alone.
