Most pulsation dampeners are selected by volume — the engineer picks a 1-litre or 2-litre unit based on pump flow rate and calls it done. The dampener is installed, the system runs, and the pulsation problem is either solved or it isn’t. When it isn’t, the usual response is to upsize the dampener volume. This misses the point entirely. Dampener volume is only one variable in the calculation, and it is not the one that has the most influence on performance. The pre-charge pressure is — and it is almost always wrong at commissioning.
How a Gas-Charged Dampener Works
A pulsation dampener is a closed vessel divided into two chambers by a flexible diaphragm or bladder. One chamber connects to the process piping; the other contains nitrogen gas at a set pre-charge pressure. When a pump discharge stroke sends a pressure pulse into the piping, the process-side chamber pressure rises above the gas pre-charge. The diaphragm flexes, compressing the nitrogen and absorbing the pulse energy. During the stroke pause, when line pressure drops below the gas pre-charge, the compressed nitrogen expands, pushing fluid back into the line and maintaining continuous flow.
The usable volume of the dampener — the volume of fluid the gas side can accept and return — is not the total internal volume. It is the volume swept by the diaphragm between the minimum and maximum operating pressures. At minimum operating pressure, the diaphragm is pushed hard against the process side by the pre-charged gas. At maximum operating pressure (the pulse peak), the diaphragm is displaced toward the gas side. The difference in fluid volume between these two diaphragm positions is the effective working volume.
Why Pre-Charge Pressure Determines Working Volume
If the pre-charge pressure is set too low — say, at atmospheric pressure — the diaphragm sits hard against the gas-side wall at all operating pressures. The dampener contains no usable gas volume because the gas has already expanded to fill the entire gas chamber. A pressure pulse entering the process side cannot compress the gas further because there is nothing to compress. The dampener is effectively inert — a dead-end volume with no pulse attenuation function. This is the most common commissioning error: a dampener installed correctly but never pre-charged to operating conditions.
If the pre-charge is set too high — above the average operating pressure — the diaphragm sits hard against the process side at average operating conditions. The gas is attempting to push fluid out of the dampener continuously. The dampener may cause the system to run above average pressure, and during stroke pauses, the gas dumps fluid back into the line aggressively rather than smoothly. This can cause flow spikes rather than flow smoothing.
The correct pre-charge is 60% of average operating pressure. At this setting, the diaphragm sits in the middle of its travel range at average line conditions, with equal working volume available in both directions. A pump operating at 4 bar average discharge pressure requires a dampener pre-charged to 2.4 bar. This sounds straightforward, but in practice: operating pressure changes seasonally or with process conditions, nitrogen slowly permeates through elastomeric diaphragms over time, and nobody checks the pre-charge at annual service.
Sizing for the Fluimac Damper Range
The Fluimac Damper is available in sizes D20, D25, D32, D40, and D50 — the designation corresponding to the connection port size in millimetres. Size selection follows three parameters: the pump’s stroke volume per cycle, the operating pressure, and the acceptable residual pulsation amplitude after dampening.
A practical starting rule for AODD pump applications: the dampener working volume should be at least 50% of the pump’s stroke volume per cycle. For a 1-inch AODD pump with a stroke volume of approximately 150 ml, the dampener working volume target is 75 ml minimum. This is the effective working volume at correct pre-charge — not the total internal volume. A D25 unit with 0.5 litre total internal volume pre-charged at 60% operating pressure will have a working volume well in excess of this target across typical operating pressures of 2–6 bar, making it appropriate for 1-inch class AODD pumps in most chemical dosing applications.
For 2-inch AODD pumps with stroke volumes of 700–900 ml per cycle, a D40 or D50 unit is appropriate. The larger port size also reduces the pressure drop penalty of routing pump discharge through the dampener, which becomes significant at higher flow rates.
The Effect of Operating Pressure on Sizing
A dampener that is correctly sized and pre-charged at 3 bar operating pressure will underperform if the operating pressure increases to 6 bar without adjustment. At the higher pressure, the diaphragm is being driven further toward the gas side at peak, and the pre-charge (still at 1.8 bar for 3 bar design) is now only 30% of operating pressure — too low. The working volume is skewed, the pre-charge is insufficient to push fluid back during stroke pauses, and pulsation attenuation degrades.
This is why systems with variable back-pressure — long discharge lines, modulating control valves, filters that increase pressure drop as they foul — require periodic pre-charge verification rather than a one-time set-and-forget approach.
Dampener Placement
A pulsation dampener must be installed close to the pump discharge to be effective. Installed 3–4 metres downstream, it attenuates pulsation in the piping between itself and the pump, but the piping between the pump and the dampener experiences the full undamped pulse. If instruments, joints, or check valves are in this upstream section, they remain exposed.
The dampener connection should be a direct tee off the main discharge header, not a long branch line. A long branch line adds its own resonance characteristics and reduces the effective coupling between the dampener and the pump pulse. For AODD pumps, the optimal placement is within 300–500 mm of the pump discharge port, upstream of the first fitting or check valve.
A correctly specified Fluimac Damper — right size, correct pre-charge, well-placed — will reduce pulsation amplitude from the 30–80% typical of undamped AODD discharge to below 10% of average operating pressure. The instruments last longer, the joints hold, and the dosing control loop sees a steady signal rather than a series of peaks.
For help selecting and sizing the right Fluimac Damper for your installation, contact Autoflo at info@autoflotechnology.com.