Pressure Gauge
We have already explained about definition of Pressure and units of Pressure etc. We have also explained about Bourdon Sensing Pressure Gauge, which is used for pressure 1 Kg/Cm2 and above. We will be explaining about pressure gauges for low pressure applications in this section.
Type of Pressure Gauge
Bourdon Tube Pressure Gauge
Diaphragm Pressure Gauge
Capsule Pressure Gauge
Bellow Pressure Gauge
Pressure Gauges for Low Pressure Applications
Bourdon sensing pressure gauges are recommended for pressure 1 Bar and above. Some manufacturers provide the same for 0.6 Bar and above. For low pressure applications, following instruments are used:
Diaphragm Pressure Gauge
Capsule Pressure Gauge
Manometer Pressure Gauge
Piezometer Pressure Gauge
Mainly Diaphragm Pressure Gauges and Capsule Pressure Gauges are used in industry for low pressure applications.
Manometer and piezometer Pressure Gauges are not much used now a days.
We have already explained about Diaphragm Pressure gauge in earlier section and, in this section, we will be explaining about Capsule Pressure Gauge.
What is Capsule Pressure Gauge
Capsule pressure gauges have Sensing element is Capsule, hence, called Capsule Pressure Gauge. The capsule element comprises two diaphragms sealed tight around their circumference. Look wise it is similar to normal Bourdon Pressure Gauges, however, in Capsule Pressure Gauges, capsule is connected to special type of movements, which are placed just above the capsule. Capsule Pressure Gauges are used for maximum pressure of 6000mm WC and minimum pressure of 60mm WC.
Construction & Working of Capsule Pressure Gauge
The pressure acts on one side of this capsule and is passed through other side, which is connected to the movement. Deflection due to pressure is shown by a pointer as measurement of pressure.
When Pressure applied to the Pressure Gauge, it pushes the capsule upwards and since, other end of Capsule is connected directly to the movement pressure is Passed on to movement depending upon the pressure applied.
Advantages of Capsule Pressure Gauge
These gauges are used for very low-pressure applications as low as 60mm WC.
Capsule Pressure gauges have compact design with better accuracy.
Capsule gauges can be supplied with back entry.
These gauges can be supplied with surface or Panel Mounting arrangements.
Capsule gauges are good option for replacing space consuming manometers.
Capsule Gauges are useful in very small vacuum measurements.
Capsule Gauges can be used as replacement to Rectangular Draft Gauges and using Capsule Gauges, we can save the space for mounting and at the same time can have more accurate readings.
It is easy to Install Accessories with Capsule Pressure Gauges
Limitations of Diaphragm Pressure Gauge
Size of capsule increases for lower pressure, hence, for very low pressure it is not possible to accommodate the capsule inside 100mm dial size, hence, one has to select 150mm dial size only.
Maximum Span of 6000mm WC is available. Though for ranges above 6000mm WC, we can select the Bourdon sensing Pressure Gauges.
Capsule Gauges are used for Air / Gas applications only.
Since, range is low, chemical Seal / Diaphragm seal is not possible for the Capsule Pressure Gauges.
Capsule Pressure gauges are costlier than diaphragm sensing pressure gauges, however, accuracy of Capsule Gauge is better than diaphragm Pressure Gauge.
Specifications Selection for Capsule pressure Gauge
Specifications are selected base on the availability, your requirement and other parameters.
Case Material (Normally SS304 or SS316)
Entry of Gauge (Bottom or Back)
Mounting (Direct / Local or Surface / Surface of Panel or Panel / Flush Panel or Bracket mounting or 2” Pipe mounting)
Dial will be with white background with black markings.
Dial sizes are normally 4” (100mm) & 6” (150mm).
Capsule & Socket is available in SS316 / SS316L.
Connection can be selected as per requirement.
Things to be taken care about the specifications Quality:
Compliance to latest EN-837 standard
Range: As per EN-837 Standard
Glass should be shatterproof safety glass and proper certificate should be asked from manufacturer.
Accuracy to be checked.
Accuracy possible is ±1% FSD.
Micrometer pointer is not possible as micrometer pointer is heavy for low ranges to deflect the pointer. Screw on dial is provided for zero adjustment.
Weatherproof certificate should be asked (latest protection certification is IP68.
Mechanical & Chemical composition certificates from NABL Accredited lab
Conclusion
Capsule Pressure Gauges have taken over the market of Manometer and Rectangular Type Draft Pressure Gauges due to its compact design, Robust Construction, choice of entry and mounting arrangements, less occupying space, better accuracy in reading. These gauges also have better enclosure protections.