Schaffer Diaphragm Pressure Gauges
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. Schaffer Diaphragm Pressure Gauges are used for pressure less than 1 Kg/Cm2 (i.e., where we are not able to use Bourdon Sensing Pressure Gauges) but it is necessary to measure the pressure span of less than 1 Kg/Cm2.
Type of Pressure Gauge
We divide pressure gauges in 4 parts:
Bourdon Type Pressure Gauge or Bourdon Pressure Gauge
Diaphragm Type Pressure Gauge or Diaphragm Pressure Gauge
Capsule Type Pressure Gauge or Capsule Pressure Gauge
Bellow Type Pressure Gauge or Bellow Pressure Gauge
We have already Explained Bourdon Type Pressure Gauges in our earlier blogs which is recommended for pressure 1 Kg/Cm2 and above only. We are well aware that temperature below 1 Kg/Cm2 is also equally important, hence, need to be measured.
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 Schaffer 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.
Most commonly used instrument is Diaphragm Pressure gauge and, in this Blog, we will be explaining about Schaffer Diaphragm Pressure Gauges.
What is Diaphragm Pressure Gauge
It is the device used to measure the pressure of fluid in a system. It is designed to measure low pressure intensities in the process. Schaffer Diaphragm Pressure Gauges are recommended for pressure range span of minimum 250mm WC to a maximum of 6000mm WC. Though Maximum range span can be even more but recommendation is up to 6000mm WC due to accuracy constraint. However, in compound range span, they are even recommended for higher ranges also.
In lower range span also, a few manufacturers are providing range span of 160mm WC, however, there are possibilities of reduced span of scale for such range.
A Diaphragm pressure gauge is a type of pressure measuring Instrument that utilizes a flexible diaphragm or membrane to sense changes in pressure. When subjected to varying pressure levels, the diaphragm deforms, and this deformation is converted into a measurable output, typically displayed on a dial.
These gauges are commonly used in various industries to accurately measure and monitor fluid or gas pressures, providing crucial information for process control and safety applications.
Schaffer Diaphragm Pressure Gauges are also known as Schaffer Pressure Gauges or Membrane Pressure Gauge.
Difference between Diaphragm Pressure Gauges and Diaphragm Seal Pressure Gauges
We have to understand that Schaffer Diaphragm Pressure Gauges are different from Diaphragm Seal Pressure Gauges. In Diaphragm Seal Pressure Gauges primary sensing element will be Bourdon and protection of diaphragm is provided, however, in Schaffer Diaphragm Pressure Guges, primary Sensing Element is Diaphragm only.
Construction & Working of Diaphragm Pressure Gauge
In Schaffer Diaphragm Pressure Gauges, Sensing element is Diaphragm as Sensor. Diaphragm element is flexible thin circular-shaped convoluted membranes.
Diaphragm is either sandwiched between two flanges or welded and is subject to the pressure of the media acting on one side.
Diaphragm’s other end is connected to the movement with the help of mechanical linkages and the deflection is used for measurement for the pressure and is indicated by a pointer.
When Pressure applied to the Pressure Gauge, it pushes the diaphragm upwards and since, diaphragm’s other end is connected to the movement with the help of mechanical linkages, pressure is converted to circular movement depending upon the pressure applied.
Advantages of Diaphragm Pressure Gauge
Wide Range Span
Diaphragm Pressure Gauges can measure a wide range of pressures, from very low to very high, depending on the specific type of diaphragm used. This versatility makes them adaptable to various industrial processes.
Compatible with all Applications
Diaphragm Pressure Gauges can be selected for almost all low-pressure Applications Starting from span of 0 to 250mm WC by selecting suitable wetted parts. Whether it is for air, water, oil, corrosive, acid applications.
Resistance to overpressure
Because of their flexible diaphragm design, Diaphragm pressure gauges can withstand temporary overpressure conditions without damage to their internal moving parts. This helps protect the gauge from damage in case of pressure spikes.
Resistance to Pulsation
Diaphragm pressure gauges can withstand pulsation as diaphragm itself acts as a pulsation dampener, which makes them more suitable for applications in industrial environments where there are pulsations.
Reliability
Diaphragm pressure gauges have simple and robust construction, which make them more reliable in the process industry over extended periods. They require minimal maintenance and have a long service life.
Local Reading
Diaphragm Pressure Gauges provide a local visual readout of pressure, which is useful for operators to monitor and control processes in real-time without relying on electronic displays.
No externa Power required
Diaphragm Pressure Gauges are completely mechanical instruments; hence, no external power is required to operate the same.
As there is no electrical component in Diaphragm Pressure Gauges, we can install them in hazardous environment.
Cost Effective
Because of their simple construction, Diaphragm pressure gauges are generally more cost-effective than some electronic pressure sensors. They offer a high level of accuracy at a lower price point, making them a budget-friendly choice for many applications.
Easy Installation
They are relatively easy to install and integrate into existing systems, making them accessible for a wide range of users and applications.
Versatility
Diaphragm pressure gauges are suitable for a wide range of applications, including HVAC systems, chemical processing, pharmaceutical manufacturing, oil and gas, and much more.
Limitations of Diaphragm Pressure Gauge
Accuracy
Accuracy of Schaffer Diaphragm Pressure Gauges are +/-2% FSD in general and as a special case, it can be provided as +/-1.6% FSD. Better accuracy is not possible in Schaffer Diaphragm Pressure Gauges because of linkages provided to join the Diaphragm with the movement. We all know that more the mechanical linkages, poorer is the accuracy. Hence, it is not possible to provide accuracy of ±1% FSD in these gauges.
Case / dial Size
It is difficult and time consuming to adjust the linkages in smaller size gauges, hence, normally Schaffer Diaphragm Pressure Gauges are manufactured for 4” and 6” dial size pressure gauges.
Only for this reason, 6” (150mm) dial size Schaffer Diaphragm Pressure Gauges are cheaper than 4” (100mm) dial size Schaffer Diaphragm Pressure Gauges.
Span
Minimum range / Span of 250mm WC is available
Maximum range / Span of 6000mm WC is recommended
Space Requirement
Size of the diaphragm is dependent on the range of the instrument. Greater the range, small will be diaphragm and for smaller ranges, diaphragm size will be bigger.
For Lower ranges, more space is required between two gauges and sometimes the space will be constraint for mounting of these gauges.
Remote Capillary type
It is not possible to provide capillary for Schaffer Diaphragm Pressure Gauges because in Schaffer Diaphragm Pressure Gauges, diaphragm is connected to the movement directly with the help of mechanical linkages.
If we have to mount these gauges remotely, we can use impulse tubing only, however, if Process fluid contains solid particles or have tendency to precipitate, it will be difficult to provide the impulse tubing because there are chances of clocking of impulse tube.
Mounting
Schaffer Diaphragm Pressure Gauges are available with bottom entry only. These are not available with back entry.
Specifications Selection for pressure Gauge
Specifications are selected base on the availability, your requirement and other parameters
Case Material (Normally SS304 or SS316)
Entry of Gauge (Bottom)
Mounting (Direct / Local or 2” Pipe mounting)
Dial will be with white background with black markings.
Dial sizes are normally 4” (100mm), 6” (150mm). Some manufacturers also provide other dial sizes also.
Diaphragm and other wetted parts are available in SS316 / SS316L as a standard. Other MOC like PTFE, Titanium, Tantalum etc., are also available depending upon the application.
Movements are available in SS304 / SS316 / Brass.
Connection can be Threaded or flanged as per user’s 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 are ±2% FSD (Normal), ± 1.6% FSD (Special)
Micrometer pointer is must. Normally manufacturers are providing normal pointer only.
Weatherproof certificate should be asked (latest protection certification is IP68.
Mechanical & Chemical composition certificates from NABL Accredited lab
Applications where Schaffer Diaphragm Pressure Gauges can be used
Can be used for Low pressure measurements
Can be used for All applications by selecting the required MOC.
Conclusion
Schaffer Diaphragm pressure gauges are valued for their accuracy, durability, and versatility, making them an essential tool in many industries where low-pressure measurement is critical for safety, quality control, and process efficiency.
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