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 is good for level measurement. Diaphragm seals, also known as chemical seals or flush seals. Diaphragm seals work with pressure transmitter, pressure gauges. To prevent 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 manufold. 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

Specifications of Diaphragm Seal Pressure Transmitter

Model Transmitter type
SI-1305 Flange level transmitter
Code Scale range
2 3 4 5 0-20~100kPa(0-2000~10000mmH2O)
Code Output form
E Linear output 4-20mAdc
SF Linear output 4-20mAdc+HART signal,Full function buttons on site
F MODBUS-485 signal
Code Flange standard (high pressure side flange)
A ANSI American Standard (HG20615)
D DIN European standard(HG20592)
Code Process connection size
ANSI American Standard (HG20615) DIN European standard(HG20592)
25 1″ DN25
40 1.5″ DN40
50 2″ DN50
80 3″ DN80
00 4″ DN100
Code Process connection withstand voltage rating
ANSI American Standard (HG20615) DIN European standard(HG20592)
A 150LB PN16/25
B 300LB PN40
C 600LB PN64
D 900LB PN100
Code Measuring diaphragm
A 316 Stainless steel
B Hastelloy C
C Monel
D Tantalum
E Titanium
F Special requirements
Code Insert barrel length Insert barrel material
A 0 mm None
B 50 mm 316L Stainless steel
C 150 mm 316L Stainless steel
D 200 mm 316L Stainless steel
Code Filling liquid
D Ordinary silicone oil  (-40~104℃)
F High temperature silicone oil   (-40~304℃)
S Inert liquid  (-40~204℃)
Code Shell material Conduit inlet dimensions
A Low copper aluminum alloy polyurethane coating M20×1.5
B Low copper aluminum alloy polyurethane coating 1/2-14 NPT
C Stainless steel M20×1.5
D Stainless steel 1/2-14 NPT
Code Optional parts
M1 0~100%  Linear indicator
M4 LCD Multi-function digital display
Da Flameproof  ExdIIBT5Gb;(explosion-proof certificate No. : CE16.1163)
Fa Intrinsically safe ExiaIICT4 / T5 / T6Ga;(explosion-proof certificate No. : CE15.2354X)
CX With corresponding 316 flushing ring

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Applications for Diaphragm Seal Pressure/ Differential Pressure Transmitters

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.

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, 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 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;

What is diaphragm seal pressure transmitter?

Diaphragm seal pressure transmitter, is the flange type pressure transmitter. This type 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 remote seals, are used for pressure measurements when the process medium should not come into contact with the pressurised parts of the measuring 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.

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 (< 600 mbar). 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.

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.

Techincal Support


How do you fill a diaphragm seal?

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 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.

How a diaphragm is used to measure pressure?

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

What are the mounting options for a diaphragm seal?

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

When are flange connections used with diaphragm seals?

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.

Sino-Instrument is pressure transmitters manufacturer in China.

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

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

Pressure transducers 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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