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.

Products

Flush diaphragm pressure transducers, transmitters, switches and gauges for measuring pressure or level that have either completely flush or semi-flush exposed diaphragms to prevent build up of material on the diaphragm and facilitate easy cleaning.

• Sanitary Process Fitting Flush Diaphragm Digital Pressure Gauges - Sanitary cleanable stainless steel process connection, open face flush diaphragm mounted digital display readout pressure gauges.
• Flush Diaphragm Voltage Output Pressure Transducers - Flush fitting pressure transducers with high level voltage outputs and exposed diaphragms for use with media requiring hygienic compatibility such as food, beverage and pharmaceuticals or viscous fluids.
• Flush Diaphragm Pressure Transmitters - Flush diaphragm pressure transmitters with 4 to 20mA current loop signal output with exposed diaphragms.
• Flush Diaphragm Pressure Gauges - Pressure gauges with exposed flush diaphragms without any internal volume within the process connection.

Pressure Sensors with Flush Diaphragms

Pressure transmitters and transducers with open flush diaphragms suitable for use with highly viscous media such as plastics, paper pulp, bitumen, sewage, paint and adhesives.

• TPFADA Flush Diaphragm Pressure Transmitter
• 35X HTC High Temperature Digital Pressure Sensor (< 300 degC)
• DMP331P Hygienic Flush Pressure Transmitter
• TPFAS Miniature Flush Diaphragm Pressure Sensor
• 35X Flush Diaphragm Digital Output Pressure Sensor
• Gefran Melt Pressure Sensor
• XMPi Process Plant Gauge and Absolute Pressure Transmitter
• x|act i Rangeable Flush Pressure Transmitter with LCD Readout
• LMK 487 Submersible Ballast Tank and Draught Level Pressure Transmitter
• DMK331P Flush Diaphragm Pressure Sensor
• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• LMK387 Cleanable Sewage and Sludge Pressure/Level Sensor
• 35X HTT High Temperature Compensated Pressure Sensor
• TPF Flush Diaphragm Strain Gauge Pressure Sensor
• 25 Ed Flame Proof Flush Diaphragm Pressure Transmitter
• DS201P High Range Flush Pressure Gauge, Switch and Sensor

Liquid Level Sensors with Flush Diaphragms

Liquid level sensors for wastewater and slurry applications requiring measurement of a few metres of liquid height with an open face diaphragm to prevent clogging. These fluid level sensors have ceramic diaphragms which are highly tolerant to abrasion and have the option for hazardous area approval for use in environments with potentially explosive gases.

• DMP331P Hygienic Flush Pressure Transmitter
• LMK331 Screw-In Ceramic Level Transmitter
• LMK351 High Overpressure Flush Level Transmitter
• LMK307 Submersible Waste Water Level Sensor
• LMK 487 Submersible Ballast Tank and Draught Level Pressure Transmitter
• LMK809 Plastic Submersible Low Level Transmitter
• LMK807 Plastic Submersible Level Transmitter
• LMK382 Low Range IP68 Waste Water Level Transmitter
• LMK387 Cleanable Sewage and Sludge Pressure/Level Sensor

Pressure Gauges with Flush Diaphragms

Battery & externally powered pressure gauges with flush diaphragms for use on viscous liquids or in applications which require high standards of cleanliness such as the in food & pharmaceutical industries.

• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DS201P High Range Flush Pressure Gauge, Switch and Sensor
• Baroli 05P High Range Flush Diaphragm Digital Pressure Gauge
• Baroli 02P Low Range Flush Diaphragm Digital Pressure Gauge

Electronic Pressure Switches with Flush Diaphragms

Solid state pressure switches with open diaphragm connections for sending a switch signal for controlling devices such pressure relief valves or a process fill pump.

• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• DS201P High Range Flush Pressure Gauge, Switch and Sensor

Corrosive Chemical Compatible Level Sensors with Flush Diaphragms

Fluid level sensors with plastic bodies and flush ceramic diaphragms for use with corrosive chemicals where no metal parts can be exposed to the media.

• LMK331 Screw-In Ceramic Level Transmitter
• LMK351 High Overpressure Flush Level Transmitter
• LMK809 Plastic Submersible Low Level Transmitter
• LMK807 Plastic Submersible Level Transmitter

Hygienic Flush Pressure Sensors for Food, Dairy & Biotech

Hygienic flush pressure transducers & transmitters for measuring pressures or level of food, beverage, dairy & biomedical product, with a crevice free exposed diaphragm that is either dry cell or back filled with food grade oil.

• DMP331P Hygienic Flush Pressure Transmitter
• XMPi Process Plant Gauge and Absolute Pressure Transmitter
• x|act i Rangeable Flush Pressure Transmitter with LCD Readout
• DMK331P Flush Diaphragm Pressure Sensor
• DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
• 35X HTT High Temperature Compensated Pressure Sensor
• DS201P High Range Flush Pressure Gauge, Switch and Sensor

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.

• Canola oil tank hygienic level sensor & indicator with high temperature protection
• Brewing tank 2000mm range 0-5Vdc output stainless steel 316L beer level sensor
• Dairy farm 6m high milk storage vat 4-20mA level transmitter
• Food processing freshwater transfer pump 4 barg 4-20mA pressure sensor
• 50-70 psi g range freshwater compatible 0-10V signal out pressure sensor for water treatment use
• 60psig range pharmaceutical pressure gauge and 0-10Vdc transducer with triclamp fitting
• 90 psi g air pressure transducer for food processes up to 200 degC
• Blow moulding machine 10,000 psi GRAS NaK filled 10V melt pressure sensor
• 10 psi g range flush diaphragm stainless steel 316L pressure transmitter
• 50 kPa negative gauge vacuum transmitter for Milk
• Beverage tank liquid level sensor for beer, wine, spirits or cider
• 30 ft high hygienic tank level transducer with 0 to 10 volt output for use with lubricants
• 10 metre high vegetable oil level transducer with 0 to 10 volt output

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.

• ELPO car paint plant 40ft high wastewater tank level transmitter
• Grease trap waste receiving tank 2m range 4-20mA level transmitter
• Water reclamation system 6 bar range pressure transmitter for marine use
• RS485 submersible wastewater level and temperature sensor for 3 metre depth
• IP68 sewage level transmitter for monitoring up to 6 metres depth of waste water

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 added to the system or interrupt the flow characteristics.