Diaphragm seal pressure transmitter, with flange connection, direct mount. Diaphragm seal systems protect pressure transmitters from hot, viscous, contaminated, or corrosive media.

Diaphragm seal pressure transmitter with flange direct mount. Diaphragm seals, also known as chemical seals or flush seals. Diaphragm seals work with pressure transmitters, pressure gauges. To prevent the process medium from entering into the pressure-sensing assembly. So, Diaphragm seal systems protect pressure transmitters from hot, viscous, contaminated, or corrosive media. Diaphragm seal connection can work with the capillary, flange, and manifold. Like remote seal pressure transmitter, DP level transmitter.

Sino-Inst offers a variety of Diaphragm Seal Pressure Transmitters for industrial pressure measurement. If you have any questions, please contact our sales engineers.

Features of Diaphragm seal pressure transmitter

Direct Mounted Diaphragm Seal System consists of gauge pressure transmitter with single direct mount diaphragm seal
  1. Diffusion silicon isolation sensor
  2. Flange installation
  3. Large size diaphragm, fully welded and sealed, long-term reliable and durable
  4. Aluminum alloy junction box with strong seal and good outdoor installation
  5. Used for pressure measurement of gas, liquid and steam
  6. Anti-corrosion metal diaphragm optional
  7. With LCD display optional
  8. Especially suitable for high temperature or viscous liquid
  9. The flange size is customized according to customer requirements. And the installation is flexible and diverse

Read more about Steam pressure transmitter-Pressure measure on steam pipeline 

Specifications of Diaphragm Seal Pressure Transmitter

ModelTransmitter type
SI-1305Flange level transmitter
CodeScale range
2 3 4 50-20~100kPa(0-2000~10000mmH2O)
CodeOutput form
ELinear output 4-20mAdc
SFLinear output 4-20mAdc+HART signal,Full function buttons on site
FMODBUS-485 signal
CodeFlange standard (high pressure side flange)
AANSI American Standard (HG20615)
DDIN European standard(HG20592)
CodeProcess connection size
ANSI American Standard (HG20615)DIN European standard(HG20592)
CodeProcess connection withstand voltage rating
ANSI American Standard (HG20615)DIN European standard(HG20592)
CodeMeasuring diaphragm
A316 Stainless steel
BHastelloy C
FSpecial requirements
CodeInsert barrel lengthInsert barrel material
A0 mmNone
B50 mm316L Stainless steel
C150 mm316L Stainless steel
D200 mm316L Stainless steel
CodeFilling liquid
DOrdinary silicone oil  (-40~104℃)
FHigh temperature silicone oil   (-40~304℃)
SInert liquid  (-40~204℃)
CodeShell materialConduit inlet dimensions
ALow copper aluminum alloy polyurethane coatingM20×1.5
BLow copper aluminum alloy polyurethane coating1/2-14 NPT
CStainless steelM20×1.5
DStainless steel1/2-14 NPT
CodeOptional parts
M10~100%  Linear indicator
M4LCD Multi-function digital display
DaFlameproof  ExdIIBT5Gb;(explosion-proof certificate No. : CE16.1163)
FaIntrinsically safe ExiaIICT4 / T5 / T6Ga;(explosion-proof certificate No. : CE15.2354X)
CXWith corresponding 316 flushing ring

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Applications for Diaphragm Seal Pressure/ Differential Pressure Transmitters

The application which is suitable for diaphragm seal system… For measuring the liquid level, density, flow, and pressure of :

  • high/low temperature fluids
  • highly corrosive/high viscosity fluids
  • the fluids which may cause clogging of impulse piping in the low temperature
  • toxic fluids
  • the fluids containing suspended solids which are deposited in the impulse piping and may cause clogging.\

Extended reading: Featured Diaphragm Seal Pressure Transmitters

Diaphragm Seal Pressure Transmitter 2

What are the application considerations for diaphragm seals?

The biggest advantage of the diaphragm pressure transmitter is that different diaphragm materials can be selected. According to different corrosion, media to achieve the best corrosion resistance. The commonly used diaphragm materials are SUS316L stainless steel. Tantalum, Hastelloy, Monel, Pure titanium, F4, etc. 

When choosing a diaphragm pressure transmitter, in addition to the correct choice of structure and range, the more important thing is to choose the material. The so-called reasonable is to consider its corrosion resistance, but also to consider the economy. For example, the corrosion resistance of the tantalum diaphragm and Hastelloy is excellent, but it is expensive. Only used in environments with high corrosivity and other cheap materials are not suitable.

The following table introduces several common corrosion-resistant materials that can be selected for corrosion media. For your reference.

Corrosive mediumTin bronze (QSn6.5-0.4)SUS316Pure tantalum (Ta)Monel (Ni70Cu30)Hastelloy (HC)Polytetrafluoroethylene (F4)
Sulfuric acid (H2SO4)VVVV
Nitric acid (HNO3)VVV
Hydrochloric acid (HCI)VV
Phosphoric acid (H3PO4)VVVVV
Acetic acid (CH3COOH)VVVV
Caustic soda (NaOH)V
Soda ash (Na2CO3)VV
Baking soda (NaHCO3)VV
Chlorine (CI)Dry: VDry: VDry: VVV
Wet: ╳Wet: ╳Wet: ╳
Bromine (Br2)Dry: △Dry: ╳Dry: ○V
Wet: ╳Wet: △Wet: ╳
Ammonia (NH3)VV
Seawater (30% NaCI)VVV
Explanation of symbols: ○ ——best; △ ——conditional use; V——can be used;

Extended reading: Common Pressure Sensor Applications

What is diaphragm seal pressure transmitter?

The diaphragm seal pressure transmitter is the flange type pressure transmitter. This type of pressure transmitter, assembling diaphragm seals to field transmitters for the purpose of measuring pressure, differential pressure, level, and flow.

What is a diaphragm seal?

Diaphragm Seals, also known as Chemical Seals or Gauge Isolators, are used to isolate pressure instrumentation, like pressure gauges, pressure transmitters, pressure switches, level transmitters, and more from process media that is hot, corrosive, clogging, or otherwise damaging to the pressure instrument.

A diaphragm seal has two primary tasks:

  1. Separation of the measuring instrument from the process medium
  2. Transfer of the pressure to the measuring instrument

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What is remote seal?

The remote seal is used to prevent the medium in the pipeline from directly entering the pressure sensor assembly in the pressure transmitter. It is connected to the transmitter by a capillary filled with fluid. As a result, they’re often used in refining, petrochemical, and chemical plants.

Extended reading: SI-703 Flush Diaphragm Pressure Sensor

What are the advantages of diaphragm seals?

Diaphragm seals offer the advantage that the “contact surface” between pressure medium and diaphragm is relatively large. Thus ensuring accurate pressure measurement, especially for very low pressures (< 600m bar). Furthermore, they can be easily dismounted, e.g. for cleaning or calibration purposes.

How do diaphragm seals work?

Basically, diaphragm seals are used in all pressure measurement processes to avoid direct contact between the measuring instrument and the medium during this process. In addition, if the measuring point cannot be installed or read because the measuring point is located in a hard-to-reach location, a diaphragm seal can also be used. In both cases, the applied pressure is transferred to the measuring instrument through the system fill fluid in the diaphragm seal housing.
The diaphragm of the seal can be made of different materials, such as stainless steel, Hastelloy, Monel, or tantalum. In addition, coatings with ECTFE, PFA, or gold can also be used.

Diaphragm Seal Pressure Transmitter 1

We can provide the best diaphragm seal design, materials, system fill fluid, and accessories for each application. The combined configuration of the pressure measuring instrument and the diaphragm seal is mainly determined by the special application conditions of the diaphragm sealing system.

How does a diaphragm pressure sensor work?

When the diaphragm seal pressure transmitter is working, the high and low-pressure side isolation diaphragms and the filling liquid transfer the process pressure to the center filling liquid. The filling fluid in the center transmits the pressure to the sensing diaphragm in the center of the δ-chamber sensor. The sensing diaphragm is a tensioned elastic element and its displacement changes with the differential pressure. For GP gauge pressure transmitters, the atmospheric pressure is applied to the low-pressure side of the sensing diaphragm. AP absolute pressure transmitter, the low-pressure side always maintains a reference pressure. The maximum displacement of the sensing diaphragm is 0.004 inches (0.10 mm). The displacement is proportional to the pressure. The two capacitance fixed plates of the measuring diaphragm are linearly converted into a 2-wire current, voltage, or digital HART output signal of 4-20mADC by the amplifying circuit.

Extended reading: How to calibrate HART pressure transmitters

Rosemount 1199 Diaphragm Seal System

Rosemount 1199 remote transmission diaphragm system provides the world’s most extensive product variety and specifications to meet the requirements of various measurements and applications.

There are the following types of remote transmission differential pressure/level transmitters:
1) PFW flat type remote transmission device
2) RTW thread installation type remote transmission device
3) EFW inserted barrel remote transmission device
4) RFW flange mounted remote transmission device
5) SCW hygienic remote transmission device

The 1199 remote diaphragm can be assembled to Sino-Inst differential, gauge, and absolute pressure transmitters and liquid level transmitters.

We can learn more about the 1199 remote diaphragms.

Techincal Support

Steam Pressure Transmitter

Steam pressure transmitters are widely used in the measurement and control of various high-temperature steam piping…

Cryogenic Pressure Transducers

Cryogenic pressure transducer for low temperature pressure measurement.  -196℃~+125℃、-260℃/-350c(especial). Sino-Inst offers a variety of Pressure Sensors…


The purpose of the diaphragm seal is to protect expensive instruments. Its job is to transfer the pressure of the process medium through the membrane seal to the filling fluid and then transmit the resulting pressure wave to a pressure gauge or sensor at the head of the measuring assembly.
Choose a suitable diaphragm seal filling liquid.
The characteristics of the diaphragm seal fill fluid determine the performance of the sealing system to a large extent. Both in response time and temperature dissipation conditions.
The initial consideration in choosing a sealed diaphragm to fill fluid is the media compatibility of the process. The temperature and pressure of the process medium are also important factors because all the filling fluid expands or contracts with changes in temperature.
Remember that there is a direct relationship between the measured response time of the viscosity and the density of the filling fluid. More viscous filling fluids lead to longer response times.
In addition, the filling fluid with a higher density can have an impact on the mounting.
Types of filling fluid: glycerin, silicone oil, and halogenated carbon are the most commonly used sealing diaphragm filling fluids.

Extended reading: Flat Pressure Sensor for High Viscosity Fluids

Diaphragm seals are mounted to existing connecting flanges or welding sockets, which are welded to a pipeline, a process reactor, or a tank.

Extended reading: extrusion melt pressure transducer

A diaphragm seal can be mounted via a direct connection, a cooling element or a capillary.

Besides pressure sensors, we also supply torque sensors. What Is a Torque Transducer? How to Choose?

The combinations of diaphragm seals with flange connections can be used for processes with extreme temperatures and with aggressive, adhesive, corrosive, highly viscous, environmentally hazardous or toxic media. With its connection dimensions, the flange-type diaphragm seal is suitable for all currently used standard flanges and is mounted in lieu of a blind flange.

Extended Reading: Resistive Pressure Transducer

Diaphragm-sealed pressure transmitters are used when the medium is corrosive or will corrode the internal parts of the transmitter (for example, ammonia will corrode the copper in the transmitter).

Extended reading: High accuracy pressure transducers

The measurement accuracy of flat film and convex film is the same, but there is a difference in the measurement structure.
The choice of the two types of diaphragms is mainly based on the different applications.
For example, in regular occasions, the material is easy to flow and not easy to crystallize and block. Just use a flat diaphragm.
If the measuring medium is easy to crystallize and block, consider the convex diaphragm structure. Of course, we must also consider the installation and pressure pipe issues.

Sino-Instrument is a pressure transmitters manufacturer in China.

We offer all types of Diaphragm Seal Pressure Transmitters. Like Direct Mounted, flange-mounted, single flange, double flange, Remote Diaphragm SealsHigh Static, Digital Remote.

Most of our Diaphragm Seal Pressure Transmitters are used in oil, liquids, DP transmitterflow measurementlevel measurement (like the ultrasonic level measurement), density, and other process variables.

Diaphragm Seal Pressure Transmitters are generally available with three types of electrical output; millivolt, amplified voltage, and 4-20mA.

You can ensure product safety by selecting from certified suppliers, with ISO9001, ISO14001 certification. We will share more about instrument calibration, like the flow transmitter calibration.

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