Proof Pressure vs. Burst Pressure in Heavy-Duty Pressure Gauges
Key Takeaways
- Proof pressure is the highest pressure a gauge can experience without drifting out of calibration.
- Burst (rupture) pressure is the catastrophic limit at which the bourdon tube will leak or fail.
- Reotemp heavy-duty gauges are proof-tested to 130 % of range (110 % above 5 000 PSI) and burst-tested to 1.5 to 10 × the rated range, depending on scale.
- ASME B40.100 recommends steady operation between 40 to 65 % of span and never above 75 %.
- Diaphragm seals introduce a second rating: Maximum Process Containment Pressure, which protects the plant from leaks.
Why Engineers Ask About “Proof Pressure”
Every instrumentation engineer has opened a spec sheet and wondered, “Will this gauge survive the start-up surge?”
Process upsets, compressor kicks, and valve slams can momentarily spike line pressure well above the normal set-point. If the spike exceeds the gauge’s proof pressure, the bourdon tube yields and the pointer never returns to zero, throwing off every subsequent reading. Surpassing burst pressure can rupture the tube, releasing process fluid and endangering personnel.
Understanding these two limits, and how they appear in standards such as ASME B40.100, lets you size gauges confidently and avoid unplanned downtime.
What Do the Terms Mean?
Proof Pressure (Over-Pressure)
ASME B40.100 definition: the maximum pressure a bourdon tube can endure without changing the accuracy of the gauge. Think of proof pressure as the elastic limit of the tube; short excursions up to this level may occur, but the gauge will spring back to its original calibration band.
Burst (Rupture) Pressure
This is the maximum pressure the bourdon tube can hold before developing a leak. Burst pressure includes a built-in safety factor, well above proof pressure, to guard against catastrophic failure. It is not a rating for routine operation.
How Reotemp Rates Its Heavy-Duty Gauges
| Gauge Range | Reotemp Proof Pressure | Reotemp Burst Pressure* | Safety Factor vs. Proof |
|---|---|---|---|
| 15 to 200 PSI | 130 % of span | 10 × span | 7.7 × |
| 300 to 1,000 PSI | 130 % of span | 5 × span | 3.8 × |
| 1,500 to 4,000 PSI | 130 % of span | 2.5 × span | 1.9 × |
| ≥ 5,000 PSI | 110 % of span | 1.5 × span | 1.36 × |
| 10 to 300 inWC (Model PC) | 130 % of span | 75 PSI (fixed) | — |
*Derived from sample burst tests on completed bourdon-tube/socket assemblies.
Tip: For pulsating services, consider a gauge one size higher than normal so that steady-state readings fall within the 40 to 65 % sweet spot recommended by ASME B40.100.
Operating Guidelines for Long Gauge Life
1. Size the Range for Normal Running, Not the Spike
- Keep continuous operating pressure between 40 to 65 % of full scale.
- Ensure that intermittent peaks never exceed the proof-pressure rating.
2. Dampen Pulsation
Sudden pressure oscillations hammer the bourdon tube. Install pressure snubbers or over-pressure protectors (limiting valves) upstream of the instrument.
3. Verify the Transient
Where possible, log the pressure profile during start-up to quantify spike amplitude and duration. A logger reveals whether you need a higher proof-pressure class, or even an electronic transmitter, instead of a mechanical gauge.
Proof Pressure Inside Diaphragm Seal Assemblies
When a diaphragm seal is welded to a gauge, you must look at two limits:
- Proof Pressure (assembly): the highest pressure the filled system—including gauge, capillary, and seal—can withstand without calibration shift.
- Maximum Process Containment Pressure: the highest pressure the seal element itself can endure without leaking process fluid.
Design Note: Because diaphragm seals add volume and flexibility, their proof pressure is often lower than the bare gauge’s. Always check the combined rating in the datasheet.
Frequently Asked Questions
Why is proof pressure expressed as a percentage while burst is a multiple?
Proof pressure relates to the elastic limit of the bourdon tube, which is proportional to material yield strength—hence a percentage of span. Burst pressure reflects ultimate tensile failure, so a multiplier better conveys the safety margin.
Can I continuously operate at 90 % of scale if the spikes stay below proof pressure?
No. ASME B40.100 limits continuous loading to ≤ 75 % of full scale to prevent fatigue and mid-scale pointer error, even if spikes are proof-safe.
What happens if I exceed proof pressure once?
The gauge may appear fine, but hidden plastic deformation can offset calibration. Always compare the reading to a reference after a suspected over-pressure event.
How do snubbers work?
They integrate a porous orifice that slows pressure rise time, converting a sharp spike into a manageable ramp below proof pressure.
Does ambient temperature affect proof pressure?
Yes. Elevated temperatures reduce material yield strength, so apply derating factors or choose a gauge certified for high-temperature service.
Conclusion
Proof pressure keeps your readings trustworthy, while burst pressure keeps your people safe. By derating to 40 to 65 % of scale, installing surge damping, and checking diaphragm seal containment limits, you can ensure that a simple mechanical gauge remains the most reliable, lowest-cost sensor in your plant.
Need a rugged gauge fast? Check out Reotemp Heavy-Duty Pressure Gauges and Reotemp Diaphragm Seal Assemblies, or contact our applications team for help specifying the right proof-pressure class.
