Installation Guide and Application Practices for Single-Flange and Double-Flange Pressure Transmitters

Overview of Flange-Mounted Pressure Transmitters

Flange-mounted pressure transmitters transmit the pressure of the process medium to the sensor body through capillary tubes or direct flange connections, enabling remote or direct measurement. Single-flange transmitters are suitable for level or pressure measurement, while double-flange transmitters are commonly used for differential pressure and level measurement in closed vessels. The Nexisense series adopts 316L stainless steel or Hastelloy diaphragms, offers a protection rating of IP67 or higher, and supports HART protocol or 4–20 mA output for easy integration with DCS systems.

In industrial applications, correct installation directly affects measurement accuracy and service life. Improper installation may cause zero drift, diaphragm damage, or signal interference. According to industry experience, standardized installation can reduce failure rates by more than 50% and ensure stable system operation.

Measurement Principles and Methods

The core principle of flange-mounted pressure transmitters is the use of an isolation diaphragm and fill fluid (such as silicone oil) to transmit process pressure to the sensing element. Single-flange transmitters measure gauge or absolute pressure and are commonly used for open tank level measurement. By detecting static pressure at the bottom flange, the liquid height is calculated based on P = ρgh.

Double-flange transmitters measure the pressure difference between the high-pressure and low-pressure chambers and are suitable for closed vessels. They eliminate atmospheric pressure effects to achieve accurate differential pressure or level measurement.

Nexisense products feature built-in temperature compensation modules to reduce errors caused by environmental changes. In level measurement applications, double-flange transmitters connect the high- and low-pressure sides via capillary tubes. The fill fluid transmits the pressure difference, ensuring measurement accuracy is not affected by fluctuations in medium density. This indirect measurement method prevents the sensor from direct contact with corrosive media, enhancing durability.

Double-Flange Pressure Transmitter Installation Guide

Double-flange pressure transmitters offer flexible installation options. They can be mounted directly at the measurement point, on a panel, or installed on a 2-inch pipe using a bracket. The flange connection ports are typically 1/4-18 NPT tapered pipe threads, with fittings of 1/2-14 NPT. The standard center distance between the two flanges is 54 mm. By rotating the flange connectors, the distance can be adjusted to 51 mm, 54 mm, or 57 mm to accommodate different process pipelines.

The installation steps are as follows. First, manually tighten the flange connector bolts to ensure sealing. Then, use a wrench to tighten them evenly, avoiding excessive force on one side. When disassembling, loosen the bolts first to facilitate removal from the pipeline. The transmitter body can rotate within the flange as long as the flange faces remain vertical, without causing zero shift. If installed horizontally on a vertical pipeline, zero adjustment is required to compensate for the hydrostatic head difference caused by the capillary height.

Location selection is critical. Avoid direct contact between corrosive or high-temperature media and the transmitter. Prevent sediment accumulation in impulse lines. Maintain balanced hydrostatic heads on both sides. Keep impulse lines as short as possible and route them through areas with stable temperatures.

Single-Flange Pressure Transmitter Installation Guide

Single-flange pressure transmitters are relatively easy to install and can be directly mounted on pipelines or tank walls via a flange. The measuring diaphragm is located at the front of the process connection and must not be touched with hard objects to prevent damage. Rotation of the transmitter body does not affect the zero point, but zero adjustment is required for horizontal installation to compensate for height differences.

The installation environment should avoid strong vibration, impact, and locations with large temperature gradients. The static pressure limit must not exceed the full-scale range, as overload may cause permanent damage. The instrument should only be removed under atmospheric pressure, and operation by professional personnel is recommended. The Nexisense single-flange series supports quick installation, offers reliable flange sealing, and is suitable for high-temperature or corrosive media.

Installation Precautions and Common Issues

Regardless of whether a single-flange or double-flange transmitter is used, the product manual must be carefully read before installation to confirm the measurement range and material compatibility. If the process medium temperature exceeds the diaphragm tolerance limit, a heat sink or extended capillary tube should be added. Shielded cables should be used for electrical connections to prevent electromagnetic interference. Before powering on, verify correct wiring. The transmitters support 4–20 mA two-wire systems or HART digital signals.

Common issues include zero drift (often caused by inclined installation), signal fluctuations (due to air bubbles or sediment), and diaphragm corrosion (due to incompatible media). On-site installation is recommended with brackets to reduce vibration effects.

Technical Parameter Reference

Typical Nexisense double-flange models offer a measurement range of 0–10 m water column (corresponding to 0–100 kPa differential pressure), with an accuracy of ±0.075% FS and an overload capacity of 200% FS. Capillary tube lengths can be customized from 1 to 15 m. The fill fluid temperature range is -40°C to 400°C.

The single-flange series provides a wider measurement range and supports absolute pressure measurement. It offers 4–20 mA + HART output, 24 VDC power supply, and a response time of less than 100 ms. Material options include 316L stainless steel, tantalum, or Monel alloy. The protection rating is IP67, with explosion-proof certification Exd II CT6. When selecting a model, consider medium density, temperature, and installation distance to ensure optimal performance.

Maintenance and Care Methods

Regular maintenance extends the service life of the equipment. Inspect flange seals quarterly and clean diaphragm surfaces using a soft cloth and neutral solvent. Avoid high-pressure washing. Calibrate zero and span annually using a standard pressure source to verify that deviation does not exceed 0.5% FS.

The minimum bending radius of capillary tubes should not be less than 50 mm to prevent fill fluid leakage. Store instruments in a dry environment and avoid extreme temperatures. Nexisense provides remote diagnostic functions, allowing status monitoring via HART communicators and early detection of potential issues.

Expanded Application Scenarios

Flange-mounted pressure transmitters perform exceptionally well in tank level monitoring, reactor pressure control, and pipeline differential pressure flow measurement. When combined with the Internet of Things, they enable remote monitoring and enhance process automation levels.

FAQ

What is the main difference between single-flange and double-flange transmitters?
Single-flange transmitters are suitable for open vessel level or pressure measurement, while double-flange transmitters are used for closed differential pressure applications and more effectively eliminate environmental influences.

How should zero drift be handled after installation?
Re-zero the transmitter or check whether the installation is level and compensate for hydrostatic head differences.

Does capillary length affect measurement?
Excessive length may increase response delay, but Nexisense optimized designs minimize this effect.

Are high-temperature media supported?
Yes. With high-temperature fill fluid options, operating temperatures above 400°C can be supported.

Conclusion

Correct installation of single-flange and double-flange pressure transmitters is the foundation for reliable measurement. From selection to maintenance, each step must be carried out rigorously. Nexisense products are recognized for their stability and ease of use, helping users build efficient process control systems. It is recommended to consult professional teams during the early stages of a project and optimize solutions based on on-site conditions to achieve long-term stable operation and promote intelligent industrial upgrading.