What is operating pressure?
It is the pressure at which the manometer will operate under normal conditions; This is defined by the user according to the process they are going to carry out. As a selection criterion, it is recommended that the selected manometer have a full scale pressure such that the operating pressure occurs in the middle (25% to 75%) of the scale.
Maximum operating pressure (MOP):
It is the maximum pressure at which the operation of the instrument can be allowed for its correct functioning without suffering any damage, which is defined by the manufacturer.
It is the reference value related to the pressure resistance of the instrument components; It refers to the design pressure given to the mechanical resistance of the internal components of the pressure gauge. The nominal pressure is usually expressed as PN.
Burst pressure:
Burst pressure is sometimes defined as the point at which something, such as a valve, hose, or pressure measuring instrument, will fail as a result of the pressure and can also be defined as the point just before failure occurs. In any case, this pressure could be considered an expression of the maximum pressure that the instrument can withstand before breaking.
It is important to consider burst pressure when designing any type of system that is used with pressurized materials such as water, gas, and various fluids. Regarding analog pressure gauges, the burst pressure is the point at which the bourdon tube stops maintaining pressure and begins to deform and split.
This represents a serious problem, since the breakage of the burdon tube not only allows the process medium to escape, but could also break the sight glass and expel metal pieces from inside the pressure gauge. If the medium is caustic, a rupture poses a danger to the environment and health. In healthcare applications, such as food/beverage and pharmaceutical/biotech, a tube rupture results in contamination, costly downtime, and the need to re-sterilize the contaminated process.
Coefficient or breaking factor:
All materials are capable, to a greater or lesser degree, of generating internal forces that oppose external forces; The unit value of resistance
that they can achieve is called “coefficient of resistance”. This coefficient can be: rupture, limit or work. The rupture coefficient marks the unit stress at which the piece breaks.
Why is the burst factor important when choosing a pressure gauge?
It lies in choosing a pressure gauge with a scale range high enough to accommodate pressure fluctuations and occasional overpressure situations.
How is the burst pressure of manometers defined?
This value It will depend on the resistance of the mechanical properties of the materials of the internal mechanism and dimensions of the instruments. However, there is no standard test in the industry that determines this factor or rupture pressure since different laboratory conditions, methods and criteria influence the process.
In effect, manufacturers do not publish burst values since this does not imply a synonym for the quality of the pressure gauge, the quality is not determined by the burst pressure.
The burst pressure values published by some manufacturers come from their own laboratory settings and criteria. Different test conditions and different methods can produce different results, making comparison of burst pressures difficult.
Another critical aspect is that real use conditions cannot be compared with laboratory conditions. When a pressure gauge is put into service, it is obvious that its use will not correspond to typical laboratory testing conditions.
The pressure that a bourdon tube can withstand depends on other variables, including:
- Mechanical vibrations
- Pulsation
- Extreme temperature
- Pressure spikes, overpressure
- Corrosion
- Shutter
- Inappropriate/excessive use
Therefore, it is important to add protective devices such as diaphragm seals, overpressure protectors, a restrictor, a shock absorber, or a relief or needle valve. A good industrial practice consists of using instruments that withstand a pressure greater than that required in the process and thus avoid damage due to pressure spikes (when the pressure increases suddenly and then drops suddenly) and thus achieve maximum work efficiency and reliability of the instrument.
In conclusion, production system design and safety requirements should not be based on gauge burst pressures. Whenever pressure may exceed the rated capacity of the measuring instrument, the system must be designed to eliminate such an event (see ASME B40.100 – 2022).