Flush Diaphragm

A guide to flush diaphragm pressure & level measurement instrumentation, including explanations, applications and a choice of products with flush process fittings.

A flush diaphragm is a type of diaphragm which is completely open and exposed to the pressure media and level or slightly recessed to the surrounding surfaces when installed.

A pressure sensing device with a flush diaphragm is installed by either clamping to a flange ring around the outer diameter of the diaphragm or using a thread which has a large enough diameter to incorporate the diaphragm at the tip of the thread.

These specialized instruments find application across a range of industries, including food and beverage processing, pharmaceuticals, chemical manufacturing, paper mills, adhesive processing, paints and coatings manufacturing and wastewater treatment. Within these sectors, they are employed by design engineers selecting components for new systems, installation engineers responsible for proper implementation, control and instrumentation engineers managing process automation, and maintenance engineers ensuring continued reliable operation. They are often found in locations where hygiene is paramount, such as clean-in-place (CIP) systems, or where viscous, sticky, or abrasive materials are involved. They are also used where the process connection needs to be kept to a minimum to avoid dead-legs or stagnation of the process media.

Flush Diaphragm Pressure Transmitters - Flush diaphragm pressure transmitters offer a specialized solution for pressure measurement in challenging applications involving viscous media, substances requiring hygienic compatibility, or environments prone to clogging.

Monitoring viscous gel filtration with a flush diaphragm data-logging pressure gauge - Prevent material accumulation and sensor clogging in thick gel filtration lines by using a high-accuracy digital gauge with a flush-mounted sensing element.
Monitoring flood levels in underground electrical substations with submersible probes - The LMK 382 provides reliable depth monitoring in underground electrical substations, featuring intrinsic safety and integrated Pt100 temperature sensing for harsh flood environments.
Ferric aluminium sulphate level sensor for monitoring coagulant tank in water treatment - Overcome corrosion and clogging when measuring ferric aluminium sulphate levels in water treatment plants using a flush-mounted ceramic transmitter.
Vacuum transmitter for chlorine, hydrogen chloride and nitrogen oxide gas with NaOH solution - Capacitive ceramic sensor with PVDF and FFKM materials provides a stable vacuum measurement in gas scrubbers containing chlorine, HCl, and NOx, plus NaOH solution.
Electrophoretic painting tank level monitoring using flush ceramic transmitters - Using high-purity alumina diaphragms and PVDF connectors to provide reliable level monitoring in aggressive chemical environments found in car paint plants.
Viscous machine tool coolant level measurement with flush diaphragm sensor - Using a flush ceramic diaphragm to prevent clogging in viscous machine tool coolant tanks, ensuring reliable level measurement for oil and water emulsions containing swarf.
Viscous soap and detergent storage hydrostatic level measurement - Flush-mounted ceramic transducer for monitoring tank levels in viscous soap and 50% sodium hydroxide applications.
Canola oil tank hygienic level sensor & indicator with high temperature protection - Instrument for measuring the level of a used Canola oil tank, and tolerate temperatures of up to 190 degrees Celsius.
Diaphragm sealed high temperature pressure transmitter for -1 to 25 kg/cm² - Diaphragm sealed pressure transmitter for measuring over -1 to 25 kg/cm² on liquid with a flush type diaphragm up to a temperature of 190°C.
2m tank height, high temperature oil level sensor with 4-20mA out - Tank level sensor to measure tank height of hot oil up to 2 meters at a maximum temperature of 200 degC.
Powder filter blockage monitoring pressure transmitter - The DMP331 is a pressure transmitter which is both ATEX and IECEx intrinsically safe approved for use in zone 20 potentially explosive dust environments.
Ebb & Flow (Flood & Drain) Horticulture Hydroponic System 100mm Water Level Sensor - We are looking for a level sensor for measuring from 0 to 100mm of water height, in an ebb and flow horticulture hydroponic system used in greenhouses and indoor farms.

Contents

Diaphragm Materials & Design

The materials used in the manufacture of flush diaphragms vary with the type of sensor technology and the intended liquid media to be measured. Dry cell sensing elements have typically have thicker and more robust diaphragms which can be used with more abrasive media such as concrete and slurries. Oil-filled sensing elements with thin stainless steel isolation diaphragms can be used in hygienic conditions and on high temperature media.

There are certain media which cannot be used with conventional pressure sensors due to it being either too viscous or requiring a high level of cleanliness.

In some test and research applications a sensor that changes the volume or shape of the vessel / pipe will lead to additional measurement uncertainties.

Threaded Style Process Connections

The most common form of flush face pressure sensor has a threaded connection with a completely open diaphragm on the end. Since the pressure connector must accommodate the surface area. of the diaphragm this leads to larger diameter threads such as 1/2 or 1 inch BSP being used in the mechanical design.

Clamped Style Process Connections

The main advantage of the clamped pressure seal over the threaded type is that there is no gap between the thread which would otherwise allow the build up of residues and bacteria. This makes it ideal for food and pharmaceutical production where very high levels of cleanliness are required.

Applications

Flush diaphragms are used in specialised applications where the media is likely to clog enclosed process connections, an increase in volume will interfere with process performance or a high level of hygiene is required. The types of liquid media which require the use of flush diaphragms include sewage, paper pulp, adhesives, paint, food, drinks, pharmaceuticals, medicines, concrete, bitumen and slurries.

High Viscosity Liquids

Substances such as paint, oil, wax, pastes, tar, plastic melt or slurries can potentially block up the process connection of a pressure sensor. The media maybe too stiff to adequately fill the internal void of a pressure connector or the substance might wax once a process has cooled down. For these types of substances it is necessary to specify a flush fitting where the diaphragm is completely open. Where there are concerns about mechanical damage to the diaphragm there are options for recessed flush diaphragms on some pressure sensors.

Pharmaceutical, Food, Beverage & Biotech

For these applications the concern is not necessarily high viscosity but more to do with cleanliness. A flush surface which is fully welded stainless steel 316 and free from crevices is the preferred sensor construction to prevent the build up of process residue, facilitate cleaning and protect against chemical corrosion. For oil filled pressure sensors it is also a requirement to use a fill that is food compatible so that if the diaphragm was to fail without being detected it would not leak any fluid into the process that would be harmful to the consumer.

Waste Water

Exposure to a waste liquid containing solids, sludge and a mixture of chemicals will lead to a highly contaminated pressure sensor. To avoid problems with corrosion and blockage of the sensor, a robust open diaphragm which can withstand the knocks from solid waste and the corrosive effects of chemical interactions is essential. The sensor must also be easy to clean and able to withstand an intensive wash down at regular intervals.

Negligible Volume

In some test and research installations there is the requirement to keep the internal volume or the effect on flow to a minimum. A conventional pressure sensor has an internal volume which may contribute a significant change in the system / test volume. If flow characteristics of a chamber / pipe are critical to measurements, a conventional pressure sensor may interfere with the measurement by changing the flow performance of the apparatus. A flush face device mounted so that the diaphragm is level with the wall of the apparatus will not add any extra volume to the system or interrupt the flow characteristics.

Related Help Guides

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Related Technical Terms

Food Grade