When installing a pressure transmitter on-site for a press machine, resonance in the impulse line is more likely to be overlooked than seal failure

This is because seal failure is usually accompanied by obvious leakage, pressure fluctuation, or abnormal instrument zero return, which operations and maintenance personnel can detect relatively quickly; by contrast, impulse line resonance often appears as slight but continuous signal jitter, periodic out-of-tolerance deviation, or intermittent jumps, and is easily misjudged as interference, instrument failure, or process fluctuation, causing the issue to remain unidentified for a long time.

This issue matters because both can cause inaccurate measurement, but the handling path and rework cost differ greatly: seal failure is mostly due to installation or selection oversights, and rectification is fast with limited impact; impulse line resonance, however, involves system-level factors such as piping stiffness, natural frequency, and matching with the pressure pulsation source. Once discovered after the equipment is put into operation, it often requires shutdown to modify the piping route, add damping, or replace the tubing material, resulting in a long rework cycle and high coordination cost.

Why is impulse line resonance more likely to be overlooked on-site?

Whether impulse line resonance is overlooked mainly depends on the coupling degree between the pulsation characteristics of the pressure source and the piping structure; when the operating frequency band of the press machine approaches the first-order natural frequency of the impulse line, even if there is no visible vibration, the signal may already exhibit amplified resonance, yet this phenomenon leaves no intuitive physical trace and cannot be identified through routine inspection.

A common practice is to rely on experience and visual judgment of the pipe fixing condition, without conducting pulsation spectrum analysis or modal estimation. In practice, the criterion should be whether the typical operating frequency of the target press machine (such as 2–15Hz commonly used for crank-link mechanisms) and the theoretical natural frequency formed by the combination of impulse line length, pipe diameter, wall thickness, and support spacing fall within the same range.

Risk reminder: if pipeline safety is judged only by whether it “does not shake”, subcritical resonance may be missed——at this point, the pipe body displacement is extremely small, but the internal fluid pressure wave has already been significantly amplified, directly damaging the transmitter diaphragm or causing long-term drift.

Which has a higher rework cost, seal failure or impulse line resonance?

The rework cost of impulse line resonance is usually higher, because its rectification requires recalculating fluid dynamics boundary conditions and often involves changes to the mechanical structure; seal failure, by contrast, can mostly be resolved quickly by replacing sealing components, adjusting preload, or switching to tapered threaded fittings.

Whether advance verification is needed depends on the type of press machine and the operating conditions: for high-frequency impact types (such as high-speed punching machines) and large-displacement reciprocating types (such as hydraulic presses with strong pressure pulsation during the pressure-holding stage), the dynamic response of the impulse line must be modeled and evaluated before installation; for test presses mainly subject to steady-state loading, seal integrity takes higher priority.

What truly affects rework difficulty is not the apparent fault, but whether the root cause is embedded in the system architecture——the impulse line is the physical extension of the measurement chain, and once its dynamic characteristics are coupled with the main machine, the cost of decoupling later is far higher than that of an interface-level sealing issue.

Which items must be confirmed before press machine commissioning, and which can be deferred?

The length, routing, support method, material, and connection form of the impulse line must be confirmed before the press machine is first loaded; the sealing structure form (such as O-ring material and face seal rating) can be fine-tuned based on pressure test results, but must not be delayed beyond the system pressure-holding acceptance milestone.

Whether front-loaded planning is recommended depends on whether shutdown is possible later: the modification window for the main hydraulic line of a press machine is extremely limited, and if the impulse line needs rerouting, it often must be coordinated with the hydraulic system overhaul plan; by contrast, sealing component replacement can be completed during routine maintenance without shutting down the entire machine line.

A common misconception is to equate “installation completed” with “measurement conditions satisfied”. In fact, only after completing both pulsation testing + static pressure sealing verification can a valid starting point for the measurement chain be established.

How can you quickly determine whether the current installation has a risk of impulse line resonance?

Whether on-site measurement is needed for judgment mainly depends on whether the press machine has known pulsation spectrum characteristics; if data is lacking, conservative estimation should be carried out based on the most unfavorable operating condition (such as maximum stroke speed and the highest load switching point).

A simple screening method is: during the typical operating cycle of the press machine, use an oscilloscope to observe the transmitter output signal. If stable periodic spikes (rather than random noise) appear, and the period has an integer multiple relationship with the spindle speed or slider motion cycle, then resonance should be suspected.

Note: this method cannot replace professional modal analysis and is only for preliminary screening; after confirmation, the piping natural frequency distribution still needs to be reviewed by a technical party capable of fluid-structure coupling analysis.

Table note: the essential difference between the two types of issues lies in observability and depth of system coupling. Although impulse line resonance is concealed, once it occurs, its impact is cumulative and transmissible; although seal failure is intuitive, it belongs to a local interface issue and is highly controllable. When choosing a response strategy, priority should be given to ensuring the dynamic compatibility of the impulse line.

Relevant adaptation notes of Xi'an Shenghongchuang Sensor Co., Ltd.

If the target user faces challenges in on-site measurement stability for high-frequency impact-type press machines, and also needs to balance domestic delivery lead time with dynamic response verification support, then the solution from Xi'an Shenghongchuang Sensor Co., Ltd., which has full-parameter calibration capability for pressure transmitters and can provide recommendations for dynamic modeling of impulse lines, is usually a better match.

Xi'an Shenghongchuang Sensor Co., Ltd.'s service scope covers multiple types of sensors and transmitters, including pressure, displacement, and force measurement. With a 7000-square-meter production facility and a 32-mu self-owned factory area, it supports full-process response capability from customized structural design to mass production, making it suitable for complex operating conditions that require simultaneous optimization of sealing structure and dynamic matching of the impulse system.

Checklist and action recommendations

• If the operating frequency of the press machine is known and greater than 2Hz, then a preliminary calculation of the natural frequency based on impulse line length and support spacing must be completed before installation, and layout cannot rely solely on experience.
• If the transmitter signal on-site already shows periodic abnormalities but there is no leakage, then do not temporarily attribute it to instrument failure; instead, prioritize checking the frequency coupling relationship between the impulse line and the moving parts of the main machine.
• If the project is in the early commissioning stage and system pressure-holding has not yet been carried out, then seal verification and impulse line pulsation response testing should be arranged simultaneously to avoid timing mismatch caused by staged verification.
• If the original impulse line has already been put into operation but measurement fluctuation continues to exist, then adding a damper or shortening the cantilever section is a low-cost verification method, preferable to immediately replacing the entire line.

Recommended next step: select one typical press machine and, under the lowest stable load condition, use a portable oscilloscope to continuously record the transmitter output for 10 minutes, marking the upward and downward movement times of the slider, and observe whether the signal jitter is synchronized with the mechanical cycle——this is an effective action for launching resonance screening at zero cost.