For specific needs not covered by conventional equipment, we design custom diaphragm seal sensors to withstand extreme conditions in sectors such as chemicals, oil & gas, paper and food & beverage.
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High-tech industries such as chemicals, oil & gas, paper mills and food & beverage put their measuring equipment to the test.
Manufacturing processes require pressure transmitters with high accuracy and reliability.
Reducing manufacturing costs means avoiding rejects and production stoppages.
The obsolescence of certain measuring devices means that replacement instruments must be found that can fit in place.
When your needs are specific, and no conventional equipment fits the particularities of your installation, we build a custom diaphragm seal sensor.
diaphragm seals are used with differential, relative or absolute pressure transmitters.
They can be mounted rigidly, directly on the sensor, or with a capillary that connects the diaphragm seal to the transmitter.
The diaphragm seal and sensor are seamlessly welded together, then filled with an oil suitable for the application.
In certain chemical or hygienic applications, it is necessary to isolate the measuring instrument from the pressure of the process fluid.
The diaphragm seal acts as a protective interface between the measuring cell and the process medium.
The diaphragm and contact parts are made of a material resistant to the process fluid, welded to the base of the measuring cell.
A capillary tube or connecting sleeve provides the junction between the diaphragm seal and the sensor's measuring cell.
This gap must be degassed under vacuum, then filled with a suitable oil and sealed.
The measured pressure exerts a force on the outer surface of the diaphragm.
As the diaphragm flexes inwards, it attempts to compress the filling fluid inside the instrument.
This filling fluid is designed to resist compression, so the force is channeled directly to the measuring cell.
The entire operation of the diaphragm seal pressure transmitter is based on Pascal's principle.
This states that a pressure exerted on a fluid is transmitted without loss through the fluid and in all directions.
For this process to work, the force required to move the membrane must be greater than the force required to move the sensitive element in the measuring cell.
In practice, this means that the lower the force required to move the measuring element, the easier it is to build an accurate sealing system.
To ensure the integrity of the manufacturing process, you need to know when to install a pressure transmitter with diaphragm seals.
pressure transmitters with diaphragm seals enable measurement of fluids at high temperatures.
diaphragm seals can be used to measure liquid flow, gas flow, steam flow, fluid level in a tank, fluid density or pressure.
For food, hygiene and pharmaceutical applications, diaphragm seals are available with hygienic fittings and flush diaphragms to meet sanitary regulations and requirements.
Several types of diaphragm seals are available, depending on mounting and application requirements:
Adapter mounting enables the diaphragm seal to be adapted to special connections, and above all to improve sensor sensitivity in special conditions.
Consult us for specific diaphragm seals .
pressure transmitters with diaphragm seals can be rigid or direct-mounted if the temperature does not exceed 150°C.
The use of a capillary limits the effects of process temperature on instrument accuracy.
A capillary length of 500 mm reduces the temperature of the instrument to room temperature.
Capillary length should be kept as short as possible, as it influences measurement accuracy and response time.
Capillaries are available from 0.5 m to 15 m with PVC (-10 to +80° C) or stainless steel (-40 to 350° C) protective sheaths.
The inside diameter is 1 mm for standard applications and 2 mm for special applications.
Temperature variations along the length of the capillary can affect instrument accuracy.
Capillary length applies to both low and high pressure sides for balanced systems.
Can be mounted on the low-pressure side only for rigid mounting and on the high-pressure side only for remote-mounted single diaphragm seal systems with capillary.
Temperature compensation must be carried out at the factory to ensure accuracy.
For applications involving corrosive fluids, diaphragm seals are available in a range of corrosion-resistant materials (stainless steel, Hastelloy C, Monel, Tantalum, Titanium, Zirconium, Nickel, etc.).
Please consult us to determine the most suitable material for your application.
The quality of the surface of the membrane and parts in contact with the fluid is very important for hygienic and sanitary applications (cleaning in place).
To prevent the risk of contamination by substances such as product residues or micro-organisms, it is necessary to check the surface finish.
Different average roughness values are available for diaphragm diaphragm seals : Ra less than 0.4 to 0.8 µm for smooth surfaces, Ra less than 1.6 µm near welds.
The diaphragm is an elastic metallic measuring element.
It needs to be as large as possible to be as flexible and sensitive as possible.
It is available in various materials (stainless steel, Hastelloy C, Monel, Tantalum, etc.) and can be fitted with coatings (PFA, PVDF, Gold, etc.) to resist the chemical aggression of the fluids being measured.
Thickness varies according to material. The membrane is welded to the diaphragm seal , and we check the tightness with a helium test.
The filling fluid used must be suitable for the temperature range of the application.
The minimum and maximum temperatures of the fluid measured, as well as the ambient temperature, must be taken into account.
In addition, the filling fluid must be compatible with the fluid being measured, particularly for fluids such as oxygen.
For applications in the food industry, mineral filling oils are available to prevent contamination of the fluid being measured in the event of membrane rupture.
| Designation | Operating temperature (°C) | Density (25°C) | |
| P abs > 1 bar | P abs < 1 bar | ||
| Silicone Oil | -40 à 180 | -40 à 120 | 0,95 |
| Fluorinated oil | -20 à 200 | -20 à 120 | 1,84 |
| Edible oil | -10 à 250 | -10 à 120 | 0,94 |
| Silicone Oil | 20 à 200 | 1,07 | |
| Silicone Oil | 0 à 300 | 20 à 200 | 1,07 |
| Silicone Oil | 10 à 350 | 20 à 200 | 1,09 |
The values given apply to the most common applications.
For special applications, please consult us, indicating ambient and process temperature, pressure to be measured, static pressure and vacuum values.
Depending on your specific operating conditions, we can use other filling fluids.
Flush rings are available as an option for diaphragm seal systems with a wide choice of materials.
The flushing ring is fitted between the diaphragm seal and the process flange connection.
It is a part in contact with the fluid.
The ring has one or two holes that can be used to rinse and clean the membrane surface.
It can also be used as a calibration ring by applying pressure through the holes.
These values must be added to the accuracy class of the pressure transmitter ±0.065% for the differential and relative pressure range, and 0.2% for the absolute pressure range.
However, vacuum accuracy cannot be guaranteed beyond 20 Torr (27mbar abs) in standard versions.
This is because most filling fluids contain microscopic quantities of trapped air or gases, which tend to expand significantly as they approach absolute zero pressure.
This expansion affects the instrument's measuring cell.
Process fluid temperature: minimum -90°C, maximum +400°C, depending on the type of filling fluid used and the diaphragm material.
The diaphragm seal pressure transmitter consists of a diaphragm seal (with or without capillary) and a pressure measurement cell.
The instrument is filled with a filling fluid at a specific temperature (usually +20 ±2°C) called the reference temperature.
A change in ambient or measured fluid temperature results in a proportional change in the volume of the filling fluid.
This has an effect on the internal pressure of the measuring system and adds error.
To minimize this error, it is necessary to compensate for the variation in volume caused by temperature.
Small-diameter diaphragms can only compensate for a slight variation in volume.
Depending on process conditions, we therefore recommend the use of diaphragm seals with the largest possible diaphragm diameter.
When the process temperature is between +150° C and +250° C, it is necessary to use a heat sink between the diaphragm seal and the measuring cell to prevent temperature diffusion.
Above 250°C, capillary diaphragm seals must be used to protect the instrument from high process temperatures.
This reduces the temperature of the measuring cell to a value close to ambient temperature.
