Pulsation and Field Balancing in Vibration Analysis Indonesia Practice
Direct answer (AEO): Pulsation analysis addresses vibration caused by pressure fluctuations in piping and machinery — the repeated gas or liquid pulses from reciprocating compressors, pumps, and engines that excite connected pipework and structures. Field balancing corrects unbalance in a rotor while it remains installed, using vibration phase and amplitude measurements to determine the correction mass and its angular position. Together they represent the two corrective techniques most often required after a vibration analysis Indonesia investigation has identified either a flow-driven excitation or a mass distribution problem, and both are performed in situ, without removing the machine from service.
Need pulsation or field balancing support in Indonesia? Contact Tiaravib — email info@tiaravib.com or WhatsApp +62 821-1378-3727.
At a Glance
- Pulsation analysis: measurement and modelling of pressure fluctuations in piping and machinery, and of the vibration they excite in connected pipework and structures.
- Field balancing: correction of rotor unbalance in place, using measured vibration amplitude and phase to calculate the required correction mass and position.
- Why both matter: these are the two corrective outcomes most frequently required after vibration analysis — one removes the excitation, the other removes the response.
- Both are in-situ techniques: they avoid rotor removal and, in many cases, avoid a shutdown entirely.
- Prerequisite for both: a correct diagnosis. Balancing a machine that has a resonance problem, or adding dampers to piping excited by a pulsation source, treats the symptom rather than the cause.
Pulsation: Understanding the Excitation Before Measuring the Response
Reciprocating machinery is fundamentally different from rotating machinery. A centrifugal compressor moves gas continuously, so the excitation it produces is smooth and predictable. A reciprocating compressor or pump moves fluid in discrete volumes, and the resulting flow is inherently discontinuous. Each cylinder discharge produces a pressure pulse, and those pulses travel through the piping as acoustic waves, reflect at changes in geometry, and can resonate with the acoustic natural frequencies of the piping system itself.
When a pulsation frequency coincides with an acoustic natural frequency of the connected piping, the pressure fluctuation amplitude can be amplified many times over. That amplified pressure fluctuation exerts a cyclic force on every bend, reducer, tee, and support in the system, and the pipe responds with vibration. If the excitation frequency also happens to coincide with a mechanical natural frequency of the pipe span or its support structure, the response is amplified again. The result is the familiar situation in which the compressor itself is running smoothly while the discharge piping shakes visibly and eventually cracks.
This is why pulsation problems cannot be diagnosed from machine vibration measurement alone. The compressor body may show acceptable vibration while the piping twenty metres downstream is approaching a fatigue limit. Field measurement must cover the piping system and its supports, and the analysis must connect the observed vibration to the pressure fluctuation that drives it.
Sources of pulsation
Several distinct mechanisms produce pulsation, and identifying which is present determines the corrective approach.
Compressor and pump displacement pulsation. The primary excitation, at multiples of running speed determined by cylinder count, configuration, and whether the machine is single or double acting. Its frequency content is a harmonic series, and the dominant orders depend on the machine’s geometry.
Acoustic resonance of the piping system. Not a source but an amplifier. The piping geometry — lengths, volumes, branch connections, and restrictions — determines the acoustic natural frequencies, and pulsation frequencies landing on those are amplified. This is why changing pipe routing can transform a benign system into a vibrating one.
Pulsation from flow control and valve behaviour. Control valves operating at low openings, check valves in unstable conditions, and cavitation all generate pressure fluctuation content that can excite the same connected systems.
Compressor surge and rotating stall. Distinct from normal pulsation and far more destructive, these produce large low-frequency pressure oscillations. Surge must be identified as such and addressed through the control and anti-surge system rather than through piping modification.
Investigating Pulsation: Measurement and Modelling
Pulsation work combines dynamic pressure measurement and dynamic stress or vibration measurement, and in the more serious cases, an acoustic model of the piping system.
Dynamic pressure transducers installed at key points along the system record the fluctuation amplitude and frequency content. Simultaneously, vibration measurement on the pipe wall at the locations of concern records the resulting structural response, and strain gauge measurement at critical locations can quantify the dynamic stress directly — which matters because the failure mechanism at issue is high-cycle fatigue, and fatigue life depends on stress amplitude rather than on displacement alone.
The analysis then establishes which pulsation frequencies are present, what their amplitudes are, which of them coincide with acoustic natural frequencies of the connected system, and which mechanical natural frequencies of pipes and supports lie near the excitation frequencies. The deliverable is a clear picture of the excitation-response chain, because the corrective measures available act at different points along it and have very different costs.
Corrective measures, from cheapest to most disruptive
| Measure | How it works | When it is appropriate | Limitation |
|---|---|---|---|
| Support and restraint modification | Changes the mechanical natural frequencies of the pipe span and increases stiffness, reducing the response to a given force | When the mechanical response, not the pressure amplitude, is the dominant problem | Does nothing to reduce the underlying pressure fluctuation; fatigue can move to another location |
| Pulsation damper or bottle sizing | Adds volume and geometry tuned to attenuate specific pulsation orders | When a small number of dominant orders can be targeted | Requires accurate acoustic modelling; incorrect sizing can amplify rather than attenuate |
| Orifice plate or restriction | Introduces acoustic resistance that damps pulsation propagation | As a targeted supplement where a specific path must be attenuated | Introduces permanent pressure drop and energy cost |
| Piping re-route or length change | Moves acoustic natural frequencies away from the excitation frequencies | When the geometry itself is resonant and the layout permits change | High cost and typically requires an outage; sometimes not feasible |
| Small-bore connection review and repair | Removes or reinforces the branch connections most vulnerable to fatigue failure under pulsation | Always, whenever pulsation-induced vibration is confirmed | Mitigates the failure consequence rather than the excitation |
The sequencing principle is that excitation reduction is preferred over response reduction, because reducing the response of one span simply relocates the stress. Where the excitation cannot be economically reduced, the response must be managed across the whole system rather than at the visible hot spot — which is why a systematic review of all small-bore connections and supports is nearly always part of a pulsation project.
Field Balancing: Correcting Unbalance in Place
Unbalance is the most common single cause of elevated synchronous vibration, and field balancing is the technique that removes it without dismantling the machine. Where shop balancing requires removing the rotor, transporting it to a balancing machine, and rebuilding the train — with all the alignment, clearance, and schedule consequences that implies — field balancing measures the machine as installed, running at operating speed, with all real-world influences present.
The principle is straightforward. Unbalance produces a rotating force whose magnitude is proportional to the unbalance mass times its distance from the axis, and whose direction is fixed relative to the rotor. That force produces a vibration response at running speed with a characteristic amplitude and phase angle. By measuring amplitude and phase, then adding a known trial mass at a known position and measuring how the response changes, the machine’s response characteristics can be determined. From that, the correction mass and its angular location can be calculated to bring the vibration to an acceptable level.
What makes field balancing valuable is that it corrects the machine in the condition in which it actually operates, including the effects of its own thermal distortion, its operating deflection under load, and the dynamics of the complete assembled train. These effects are precisely what a shop balance cannot reproduce, and they are a common reason a machine that balanced perfectly on the balancing machine vibrates when reinstalled.
When field balancing is the right answer
Field balancing is indicated when the diagnosis confirms unbalance as the dominant mechanism: vibration dominated by the running-speed component, a phase angle that is stable and repeatable across measurements, and an amplitude that responds predictably to speed changes through the critical region but remains consistent at steady state. It is further indicated when the machine cannot be removed without disproportionate cost or outage, or when the machine is large enough that removal is impractical.
It is not indicated when the vibration at running speed is caused by a resonance or a critical speed rather than by unbalance. In that case, balancing will reduce the amplitude because it reduces the excitation, but the machine returns to the original condition as unbalance naturally re-accumulates — often within weeks. The correct approach in that situation is rotordynamic investigation of the resonance condition, as covered in rotordynamic analysis.
The field balancing procedure
A disciplined field balance follows a fixed sequence, and skipping the early steps is what produces poor results.
1. Verify the diagnosis and the measurement. Confirm that single-plane or two-plane balancing is appropriate, that the vibration is genuinely synchronous and stable, and that the measurement points are suitable. Verify tachometer pickup consistency, because the entire calculation depends on a reliable phase reference.
2. Establish a baseline. Record vibration amplitude and phase at running speed at each measurement plane before any change is made. Repeat it to confirm that the reading is stable enough to work with.
3. Run a trial mass and measure the response. Add a known mass at a known angle, run the machine to the same condition, and measure the new amplitude and phase. This single trial run establishes the influence coefficients that describe how a mass at a given position affects the vibration at each measurement point.
4. Calculate the correction. From the baseline and trial-run data, solve for the mass and angle that minimise the remaining running-speed vibration. For a two-plane balance, both planes must be solved simultaneously because a mass in one plane affects the response in the other.
5. Install the correction and verify. Fit the computed correction, run to the same stable condition, and measure. If residual vibration remains above target, repeat with the updated influence data rather than starting over — each iteration improves the model of the machine’s response.
6. Document the result and the final state. Record the correction mass and angle installed, the residual vibration level, and the running condition. That record becomes the baseline for all future monitoring, and it is what allows a later vibration increase to be judged against a known residual rather than an unknown one.
Why Both Techniques Belong in a Vibration Analysis Programme
Pulsation work and field balancing are usually presented as separate specialisms, and technically they are. But from an operating plant’s perspective they occupy the same position: each is a corrective action that a vibration analysis programme recommends once a diagnosis has been completed, and each is performed with the machine essentially in service.
That shared position matters for how a programme is organised. A monitoring service that can diagnose a problem but cannot correct it leaves the plant with a finding and a search for a contractor. A programme that covers measurement, diagnosis, and correction end to end compresses the interval between detection and resolution, and that interval is where most of the consequential damage in a developing failure occurs. It is also where the credibility of the programme as a whole is decided: findings that result in visible, measured improvement build support for condition monitoring far more effectively than any number of reports.
How Tiaravib Delivers Pulsation and Field Balancing
Tiaravib has provided vibration engineering and reliability services to Indonesian process, power, and manufacturing operators since 1995, and both pulsation analysis and field balancing are delivered as part of the reliability services range rather than as isolated field jobs.
For pulsation, the work begins with the measurement campaign: dynamic pressure transducers at selected locations, vibration measurement across the piping system and its supports, and where the risk warrants it, dynamic strain measurement at the connections most vulnerable to fatigue. The analysis connects the measured pressure fluctuation content to the observed structural response and identifies both the acoustic and mechanical natural frequencies involved. The recommendations then follow the preference order of excitation reduction first — damper sizing, orifice placement, or geometry change where feasible — with support and restraint modification and a systematic small bore pipe connection assessment as the response-side measures that protect the system while the primary fix is implemented.
For field balancing, we balance in single and two-plane configurations on fans, pumps, motors, turbines, and large compressor trains. Before any balancing work begins, we confirm that unbalance is genuinely the dominant mechanism rather than a resonance or a critical speed problem, because performing a balance on a resonant machine produces temporary improvement and a repeat visit. Where the diagnosis points elsewhere, the job becomes an investigation rather than a balance, which is the more useful outcome for the client even though it is not the job that was originally requested.
Both techniques feed back into ongoing monitoring. The residual vibration level and correction data from a balance become the reference for future trend assessment, and the pulsation findings shape the vibration alarm strategy on the affected system. Since pulsation problems frequently originate in reciprocating machinery, the work links directly to reciprocating engine and compressor analysis, and where flow-driven excitation involves rotating equipment, to flow induced vibration analysis and piping vibration assessment.
The American Society of Mechanical Engineers maintains the balancing standards that define the acceptance grades applied to rigid and flexible rotor balancing work.
Key Takeaways
- Pulsation is an excitation problem. Reciprocating displacement creates pressure pulses that pipe acoustics amplify, and the compressor body may show nothing while the piping fails.
- Fatigue is a stress mechanism. Pulsation-induced failure depends on dynamic stress amplitude, so dynamic pressure, vibration, and strain measurement are all required.
- Reduce excitation before response. Adding supports reduces the response at one span and can relocate the stress; attenuating the pulsation addresses the cause.
- Field balancing works on the installed machine. It captures thermal and assembly effects that a shop balance cannot, which is why the results often differ.
- Never balance a resonance. If the running-speed vibration comes from a critical speed, balancing gives temporary relief and the problem returns as unbalance re-accumulates.
- Document the residual. A recorded post-balance vibration level becomes the reference that makes every future reading interpretable.
Frequently Asked Questions
How do we know whether a piping vibration problem is pulsation or mechanical?
Measure both the pressure fluctuation and the pipe vibration at the same time. If the pressure fluctuation amplitude is low while the pipe response is high, the problem lies in the mechanical response, typically a support or span natural frequency, and support modification is the likely solution. If the pressure fluctuation is substantial and its dominant frequencies match the pipe vibration content, pulsation is the driver and must be addressed at the source or through acoustic attenuation. If both are moderate but the frequencies coincide with a mechanical natural frequency, the system is being amplified by resonance and the fix is to separate the frequencies. Measurement of both quantities simultaneously is what makes the distinction possible.
Can field balancing be done without taking the machine out of service?
In most cases yes, and that is its principal advantage. The machine is run at operating condition for the baseline and trial runs, which requires it to be available for those periods but not removed or stripped. Where the machine can be run through a normal operating cycle, balancing is usually completed within a single shift or two, depending on the number of planes and the stability of the readings. The exception is where the machine cannot be run at a stable condition — for example, where process demand changes continuously — in which case the repeatability required for reliable influence coefficients is difficult to achieve and the balancing window must be planned around a period of stable operation.
How many balancing runs are normally required?
A single-plane balance typically needs the baseline run, one trial mass run, and one verification run after installing the calculated correction, with further iterations only if residual vibration remains above target. Two-plane balancing follows the same pattern but the trial and correction runs must be handled simultaneously, and a second trial run is sometimes useful to improve the confidence in the influence coefficients. In practice, three to five runs completes most jobs. The determining factor is measurement repeatability: if phase and amplitude readings are stable, the calculation converges quickly, and if they drift, no amount of additional runs will produce a reliable result until the source of the instability is found.
What is the difference between single-plane and two-plane balancing?
Single-plane balancing is appropriate when the rotor is relatively short in relation to its diameter, when it operates below its first critical speed, and when the unbalance can reasonably be treated as acting in one plane. Two-plane, or dynamic, balancing is required when the rotor is long relative to its diameter, when it operates near or above the first critical speed, or when vibration measured at the two bearings shows significantly different phase behaviour that indicates the unbalance is distributed or includes a couple component. Choosing single-plane for a rotor that requires two-plane correction produces a result that improves one bearing while worsening the other.
How much can field balancing actually reduce vibration?
Where unbalance is genuinely the dominant mechanism and the measurement is reliable, field balancing can typically reduce running-speed vibration to a small fraction of its original level, often approaching the machine’s residual dynamic response. The limiting factors are not the technique but the surrounding conditions: if the machine has a significant resonance, or if the remaining vibration contains substantial content from misalignment, looseness, or structural response, then the running-speed component can be brought down while overall vibration remains elevated. This is why the diagnosis must precede the balance — the measurable improvement realistic to expect is set by how much of the vibration is actually caused by unbalance.
How often should a machine be re-balanced?
Balancing corrects the unbalance present at the time it is performed; it does not prevent unbalance from developing again. Re-balancing becomes necessary when condition monitoring shows the running-speed vibration component trending upward, which typically indicates deposit build-up on fans and impellers, erosion, component shift, or material loss. The interval is therefore determined by the machine’s service rather than by a schedule: a fan in a dirty gas stream may need attention far more often than a clean-service pump. This is one of the clearest illustrations of why continuous monitoring and corrective work belong in the same programme — the monitoring identifies when the balance has drifted, and the balancing restores it before the vibration reaches a damaging level.
External references: ISO 20816 mechanical vibration measurement and evaluation, American Petroleum Institute standards for reciprocating machinery, and the U.S. Department of Energy.
For a site assessment or pilot proposal, contact Tiaravib via WhatsApp +62 821-1378-3727 or info@tiaravib.com.
