Single Flange Level Transmitter for Harsh & Explosive Process Environments
1. Why You Need a Single Flange Level Transmitter
Open tanks, closed vessels and crystallizing-media tanks all share one challenge: the liquid you are measuring is often hot, viscous, corrosive, or prone to depositing solids. Conventional gauges with a wet pressure port quickly clog, and gauge-pressure transmitters that vent to atmosphere drift when vapor pressure builds inside a sealed tank. A single flange level transmitter removes the pressure tapping point entirely — a large flush diaphragm seals directly against the process and converts hydrostatic head into a clean 4-20 mA HART signal, so the wetted surface resists build-up while the electronics stay isolated from the process. This makes it the standard choice for vacuum systems, reactors and storage tanks where atmospheric pressure influence must be cancelled out and where absolute process containment matters.
2. Working Principle of the Single Flange Level Transmitter
The transmitter measures the hydrostatic pressure exerted by the liquid column above the diaphragm. This pressure is proportional to liquid level, media density and gravity. A large-diameter sensor diaphragm — typically 316L, with Hastelloy C, tantalum or PTFE available for aggressive media — transmits the pressure to an internal sensing element. The transmitter compares the process pressure against a stable reference and outputs a linear 4-20 mA signal superimposed with HART digital communication. Because the flange diaphragm is flush and pressure-port-free, media that crystallizes, settles or is highly viscous cannot plug the sensing path, and the one-piece welded housing keeps the electronics protected from the process atmosphere.
3. Single Flange Structure Advantages
- Clog-resistant flush diaphragm: no pressure tapping hole, so viscous, crystallizing and particulate media cannot block measurement.
- Explosion-proof isolation: flameproof DII BT4 construction separates the electronics from hazardous process vapors.
- High static pressure capability: a single sealed flange handles wide span ranges from 0-6 kPa up to 10 MPa.
- Measurement accuracy: selectable accuracy grades of 0.075%, 0.25% or 0.5% to match your control budget.
- Long-term reliability: temperature self-compensation and automatic drift correction keep output stable in harsh industrial environments.
Q: What is a single flange level transmitter?
A single flange level transmitter is a differential-pressure instrument that measures liquid level by sensing the hydrostatic pressure exerted by the liquid column on a flush-mounted diaphragm. One side of the sensor is sealed by a flange diaphragm in contact with the process, while the reference side compensates for vapor or atmospheric pressure. This design is ideal for viscous, crystallizing, corrosive or high-temperature liquids because there is no narrow pressure port to clog. The transmitter outputs a standard 4-20 mA signal, often with HART digital communication, allowing direct integration with DCS and PLC control systems in chemical, petrochemical, power and water-treatment plants.
Q: What is the difference between a single flange and double flange level transmitter?
A single flange transmitter uses one flange-mounted diaphragm on the process side and a direct reference, and is typically applied to open tanks or closed vessels where the vapor side is handled through a vent or capillary. A double flange transmitter uses two remote flange diaphragms connected by capillaries — one at the top and one at the bottom of the vessel — to measure the full differential pressure across the liquid column. Double flange is preferred for closed, pressurized tanks with a meaningful vapor space, while single flange is simpler and often more economical for open or low-vapor-pressure applications.
Q: Can a single flange level transmitter measure corrosive liquids?
Yes. The wetted diaphragm is available in 316L stainless steel for general corrosive media, Hastelloy C for strong acids and alkalis, tantalum for highly aggressive acids, and PTFE for chemical compatibility in specific applications. Choosing the right diaphragm material is essential for service life and measurement accuracy. Our team helps match the diaphragm and seal material to your specific process chemistry and temperature so the transmitter operates reliably without premature corrosion or drift.
Q: Why is the flush diaphragm design important?
A flush diaphragm sits nearly level with the flange face, eliminating the cavity or pressure port where solids, crystals and viscous media accumulate. In processes involving sludge, syrup, crystallizing salts or polymer melts, a recessed port would gradually plug and produce false readings. The flush design keeps the sensing surface clean and in direct contact with the liquid, ensuring stable, repeatable measurement and dramatically reducing the cleaning and maintenance frequency required for the instrument.
Q: What is the accuracy of a single flange level transmitter?
Accuracy depends on the model and configuration. Our single flange transmitter offers selectable accuracy grades of 0.075%, 0.25% and 0.5% of span. The 0.075% grade suits custody-critical and high-precision control loops, while the 0.25% and 0.5% grades provide cost-effective options for general process monitoring. Intelligent models also include temperature compensation and automatic zero drift correction, which help maintain the specified accuracy over wide ambient and process temperature ranges.
Q: Where are single flange level transmitters used?
They are widely used in petrochemical, steel and metallurgy, water and sewage treatment, environmental protection, papermaking, food processing, power generation and agriculture. Typical applications include reactor and storage tank level, sedimentation and reservoir level, high-viscosity product tanks, and any process where the medium is hot, viscous, corrosive, crystallizing or settling. They are also used with orifice plates and vortex flowmeters to build automatic metering systems.
Q: What output signal does it provide?
The standard output is a two-wire 4-20 mA DC analog signal, which is compatible with virtually all industrial control systems. The signal can be superimposed with the HART protocol for bidirectional digital communication, allowing remote configuration of range, damping and diagnostics without removing the transmitter from service. This combination of analog and digital output makes the instrument both easy to integrate and convenient to maintain.
Q: Is it suitable for explosive atmospheres?
Yes. The transmitter is available in a flameproof DII BT4 explosion-proof housing, which is rated for use in hazardous areas where flammable gases or vapors may be present. The one-piece welded enclosure and isolated wiring chamber prevent internal sparks from reaching the external atmosphere. Always verify the area classification against the rating before installation and follow local electrical codes for hazardous-area wiring.
Q: How is the transmitter installed?
The transmitter mounts via a standard flange (DN50 or DN80, customizable) on the lower side of the tank or vessel where the liquid column acts directly on the diaphragm. The flange should be properly aligned and sealed to prevent leakage. Electrical connection uses a two-wire terminal inside an isolated chamber, and the cable should be routed downward to prevent moisture ingress. After installation, a zero and span calibration is recommended to confirm measurement accuracy.
Q: Can it measure pressure and density as well as level?
Yes. Because the instrument measures hydrostatic pressure, it can be used to derive not only liquid level but also process pressure and media density in many installations. When combined with orifice plates or vortex flowmeters it can form part of an automatic metering and control system. This multi-parameter capability makes the single flange transmitter a versatile component in a plant's overall process instrumentation.
