Accurately and reliably measuring the level of liquids in tanks, vessels and silos can be a fundamental requirement among industrial process control domain. Pressure and differential pressure (DP) transmitters are the workhorses for such applications, inferring level by measuring the hydrostatic pressure exerted by the fluid.
When Direct Mounting Fails
A standard pressure or DP transmitter is typically mounted directly at the process connection port with its sensing diaphragm in direct contact with the process medium. While this is effective for benign fluids like clean water, some industrial scenarios make this direct approach impractical:
High-temperature Media: Extremely hot process fluids can exceed the safe operating temperature of the transmitter's electronics and sensor. The heat can cause measurement drift, damage internal components and dry the fill fluid inside.
Viscous, Slurry, or Crystallizing Fluids: Substances like heavy crude oil, pulp, syrup, or chemicals that crystallize upon cooling can clog the impulse lines or the small bore leading to sensing diaphragm. This leads to sluggish or entirely blocked measurements.
Corrosive or Abrasive Media: Acids, caustics, and slurries with abrasive particles can quickly corrode or erode the delicate sensing diaphragm of transmitter, causing instrument failure and potential process leaks.
Sanitary/Hygienic Applications: In food, beverage, and pharmaceutical industries, processes require regular cleaning-in-place or sterilization-in-place. Transmitters must be designed without dead legs or crevices where bacteria can grow, making standard direct-mount units non-compliant.
Process Pulsation or Vibration: In applications with significant pulsation or mechanical vibration, mounting a transmitter directly to the vessel can transmit these forces to the sensitive sensor, resulting in noisy, unreliable readings and potential mechanical fatigue.
Introducing the Remote Diaphragm Seal System
A remote diaphragm seal (also known as a chemical seal or gauge guard) is a system designed to protect the transmitter from these hostile conditions. It acts as a robust, isolating barrier consisting of three key components:
Seal Diaphragm: A flexible, corrosion-resistant membrane (often made from SS316, Hastelloy, Tantalum or PTFE-coated materials) that is in direct contact with the process fluid via flange or clamp connection. The diaphragm deflects in response to process pressure.
The Capillary Tube: A sealed capillary filled with a stable, incompressible system fill fluid (such as silicone oil and glycerin). The tube connects the diaphragm seal to transmitter's sensing diaphragm.
The Transmitter: The pressure or DP transmitter itself, now isolated from the process medium at a distance
The operating principle is based on Pascal's Law of fluid pressure transmission. Process pressure acts upon the remote seal diaphragm, causing it to deflect. This deflection pressurizes the fill fluid inside capillary system that then transmits this pressure hydraulically through the capillary tube to the transmitter’s sensing diaphragm. Thus it measures the pressure accurately without ever coming into contact with the troublesome process condition.
Key Advantages and Strategic Benefits
The implementation of a remote seal system offers a multitude of advantages that translate directly into improved operational efficiency, safety, and cost savings.
Unparalleled Instrument Protection and Longevity:
Acting as a barrier, the remote seal takes the full brunt of the process conditions and the transmitter is shielded from extreme temperatures, corrosion, abrasion and clogging. It dramatically extends the service life of the transmitter, reducing replacement frequency and total cost of ownership.
Enhanced Measurement Accuracy and Reliability:
In direct-mount scenarios, clogged impulse lines are a major source of error. Remote seals eliminate the need for long impulse lines which is a potential point of failure. The system provides a direct, clean hydraulic link to the process, ensuring responsive and accurate readings, even for viscous or slurry-type fluid.
Unlock Measurement in Extreme Temperatures:
Remote seals can be selected with specialized materials and fill fluids rated for very high or cryogenic temperatures. The transmitter can be mounted at a safe distance from the heat source, ensuring its electronics operate within their specified temperature range. This is crucial in applications like reactor vessels, boiler drums, or cryogenic storage tanks.
Simplified Maintenance and Reduced Downtime:
When the process connection require maintenance, a transmitter with a remote seal can often be isolated and removed without draining the entire vessel. Furthermore, if the seal itself becomes damaged, it can be replaced independently of the transmitter, which can be a far less costly and quicker repair.
Flexibility in Installation:
The capillary tube allows the transmitter to be mounted in the most convenient and accessible location—away from high-vibration areas, hard-to-reach spots on top of a tank, or confined spaces. This simplifies installation, calibration, and routine maintenance checks.
Ensuring Process Purity and Sanitation:
In hygienic industries, flush-mounted diaphragm seals provide a smooth, crevice-free surface that is easy to clean and sterilize, preventing bacterial contamination.
The remote diaphragm seal is a strategic solution for reliable and accurate level measurement in some of the most demanding industrial environments. By creating a protective barrier, it allows pressure and differential pressure transmitters to perform their duties safely and effectively, far removed from the corrosive, clogging or thermally extreme realities of the process. Shanghai Wangyuan is a high tech manufacturing company specializing in production and service of pressure measurement instrumentation with over 20 years experience. Should you have any requirements or questions regarding remote diaphragm seal transmitters, please do not hesitate to contact us.
Post time: Nov-17-2025