Diaphragm Seal Pressure Gauges: The Key to Precision in 8 Critical Industries

An Introduction about Diaphragm Seal Pressure Gauges

Bourdon Sensing pressure gauge for special applications like corrosive / Hazardous / Viscous fluids or for fluids with solid particles or Sediments or having tendency to crystalize / solidify / Freeze, cannot be used directly because of various reasons.

Pressure Gauges are recommended to use with Diaphragm Seal Unit, to avoid entering of fluid inside the Bourdon.

We have already explained what Pressure Gauge is, Bourdon Tube Type Pressure Gauge Construction, Working Principle, Important Parts, Specification Selection, Things to be taken care about quality in earlier Blog “172 Years of Precision – Bourdon Tube Pressure Gauge and Its Most Important Parts”

What is Diaphragm Seal Pressure Gauges

inside the bourdon as bore of bourdon is very fine.  Protection is provided with a flexible membrane (which is called as diaphragm). 

Instrument side of the diaphragm is filled with appropriate fluid called sealing fluid.  Some people call it as diaphragm seal and some call it as chemical seal.  Pressure gauge duly fitted with Diaphragm Seal are called Diaphragm Seal Pressure Gauges.

How Diaphragm Seal Pressure Gauges work

Pressure exerted by the process fluid on the diaphragm is hydraulically transmitted through the seal fluid to the pressure sensing element.  Since,           fluid is not entering inside the bourdon, it protects the sensor from the harmful and hazardous effect of the process fluid.

We know that as per Newton’s third Law, action and reaction are equal and opposite, hence, when pressure exerted on the diaphragm, it pushes the fill fluid filled above diaphragm and at the same time, fill fluid exert same amount of pressure on the diaphragm.

When Pressure below the diaphragm is reduced, diaphragm is pushed back by the fill fluid up to the extent of difference in the pressure and when there is no pressure below the diaphragm, diaphragm return back to its normal position.

When to opt for Diaphragm Seal Pressure Gauges

Process fluid is corrosive

Process fluid is Highly Viscous

Process fluid is having Sediments or Solid particles

Process fluid having tendency to crystallize, solidify, freeze when temperature decreases

Process fluid is hazardous in Nature.

Why to opt For Diaphragm Seal Pressure Gauges

Corrosive fluid by entering in the normal can damage / Corrode the internal parts of the Pressure Gauge and with passage of time, this can lead to inaccurate reading. 

Corrosion can weaken some of the internal parts from the point, where it becomes safety Hazards, Use of such compromised gauges can cause big damages.

Solid parts or contaminants can clog or damage the internal parts, which can affect the gauge accuracy and lifespan.  This can also affect the end product quality and can even spoil the final product completely.

Gauge without seal requires frequent maintenance and replacement.  Cost of maintenance will be higher than the cost of Instrument.

So, using a Diaphragm Seal Pressure Gauges, one can ensure the accuracy and longevity of the pressure gauges in corrosive applications.  It also protects the process, equipment and person standing in front of the gauge.

It is equally important to use the right type of Diaphragm Seal Pressure Gauges depending up on your process parameters and process fluid

Applications of Diaphragm Seal Pressure Gauges

Chemical Industry

There are applications where we are handling corrosive fluids, acids and high temperature solutions etc., where we can use the Diaphragm Seal Pressure Gauges.

Refinery and Petrochemical

We can use the Diaphragm Seal Pressure Gauges for various corrosive services like HCL Injection System, Sulphur Recover Unit (SRU), Catalytic Cracker Units (FCCU’s), Hydrogenation Units for Desulfurization.

Pharmaceutical and Biotechnology

We can use the Diaphragm Seal Pressure Gauges for Various processes like Fermentation, Sterilization. Special Diaphragm Seal Pressure Gauges are used, which are easy to remove and install as for these applications we need to sterilize the instruments after every batch process.

Food and Beverage

We can use the Diaphragm Seal Pressure Gauges for Various processes where we use Special Diaphragm Seal Pressure Gauges which are easy to install and remove as sterilization is required after every batch.

Oil and Gas

There are Applications, where we are handling Sour Gases, Hydrogen Sulphide, Slurries, Crude Oil, offshore drilling, Well Testing, Chemical Injection System, where we can use the Diaphragm Seal Pressure Gauges.

Water and Wastewater Treatment

There are applications of Chemical Injection System, RO Process, Filtration Process, Wate water handling, Chemical storage and Handling, where we can use Diaphragm Seal Pressure Gauges.

Power Generation

Diaphragm Seal Pressure Gauges are used in power plants for pressure measurement in various applications of Steam Generation, turbines, and cooling systems.

Aerospace and Defence

Diaphragm Seal Pressure Gauges play a role in aircraft hydraulic systems, missile propulsion, and other critical applications.

Construction of Diaphragm Seal

Non-Wetted Parts

CS, SS304 & SS316

Diaphragm

SS316, SS316L, PTFE, PTFE Coated SS, Titanium, Monel, Nickel, Hastelloy B, Hastelloy C, Tantalum, Duplex SS, Super Duplex SS

Wetted Parts

SS316, SS316L, SS with PTFE Coating, PTFE Lining or PTFE block, Monel, Hastelloy B, Hastelloy C, Duplex SS, Super Duplex SS

Sealing Fluid / Filling Fluid

To be selected depending on Temperature and application

Capillary

Capillary material

SS304, SS316, SS304 with SS304 Armoring, SS304 with SS316 Armoring, SS316 with SS316 Armoring, SS304 with PVC covering, SS316 with PVC Covering

Capillary Length

Length of capillary is equally important, however, for small ranges, it is better to select smaller lengths of capillary to maintain response time.  If range is small and capillary length is more, response time will be poor.

Different type of Sealing Fluids

Fluid	Temperature Suitability
Silicon Oil, DC 200 Grade	-45 Deg. C to 200 Deg. C
Silicon Oil, DC 704 Grade	0 Deg. C to 315 Deg. C (is replaced by Siltherm 800)
Silicon Oil, DC 705 Grade	20 Deg. C to 350 Deg. C
Silicon Oil, DC 710 Grade	5 Deg. C to 345 Deg. C
Fluorolube Oil	-40 Deg. C to 150 Deg. C
Glycerine	15 Deg. C to 80 Deg. C
Halocarbon Oil	-40 Deg. C to 235 Deg. C
Food Grade Vegetable Oil	5 Deg. C to 182 Deg. C

Different Types of Seals

Sandwich Type, Threaded

In Threaded type Sandwich Type Diaphragm seal, diaphragm is sandwiched between two flanges

Flanges are either bolted or welded to fix the diaphragm

Sandwich Type, Flanged

In Flanged type Sandwich, Diaphragm seal, diaphragm is sandwiched between two flanges

Flanges are either bolted or welded to fix the diaphragm

Connection is provided by way of I Section

Flush Diaphragm Type, Threaded (Mini Diaphragm Seal)

In Flush Diaphragm Threaded type seal unit, diaphragm is Welded at the bottom where bore is provided

Minimum Size available for these seals will be 3/4″

Connection Size availability is subject to range requirement

Recommended for Highly Viscous or Crystallizing fluids

Flush Diaphragm Type, Flanged

In Flush Diaphragm Flanged type seal unit, diaphragm is Welded on the RF portion of the flange

Minimum Size available for these seals will be 1″

Connection Size availability is subject to range requirement

Recommended for Highly Viscous and Containing Solid Particles.

Extended Diaphragm Type

Extended diaphragm seal is mounted on the Nozzle flange of process pipe line

Diaphragm is extended to the process media through the nozzle.

Length and diameter of the extension is decided as per process requirement and nozzle diameter.

Diaphragm is directly extended through the nozzle & preventing clogging

Inline Flow Through Type (Flanged / Welded). Possible with jacketed type

In-Line flow through type seals are directly installed in process flow line, hence, called In-Line flow though type seals.

These are designed in such a way that diaphragm is essentially flush with the flow stream so that process media itself wash the diaphragm.

Recommended when process media is slurry or Containing Solid Particles.

Flange connection can be provided as per process requirements. Min. Size available is 1/2″

Inline flow through type with cylindrical diaphragm

In-Line flow through cylindrical type seals are directly installed in process flow line between 2 flanges.

These are also called as cell type diaphragm seal unit.

Area behind the diaphragm is filled with filling fluid and pressure flowing through the pipe exert pressure on the cylindrical diaphragm.

Minimum flange Size of 1″ is available for these.

Recommended when process media is slurry or Containing Solid Particles.

Pressure exerted on cylindrical diaphragm is transmitted to Instrument through fill fluid

Inner diameter is of the seal unit is provided same as that of process pipe, so it is continuously cleaned by the flowing process media.

It avoids clogging, resulting in accurate reading.

Pan Cake Type

Pan Cake Diaphragm Seal is sandwiched between Instrument flange (called as loose back-up flange) and process flange.

Diaphragm is welded directly on pan Cake

Connection Size availability is subject to range requirement

It is available with capillary only.

Minimum Size available for these seals will be 1-1/2″

There are no cavities where process fluid can enter or clog the system.

Hygiene Diaphragm Seal

Hygiene Diaphragm seals are designed for pressure instruments in Sanitary applications.

Gauges with Tri-clover, SMS Union and IDF Fitting connection are generally available.

Hygiene gauges are used in Pharmaceutical, dairy, biotechnology, food and beverages Industries

Can be provided with or without IDF male coupling, SMS male coupling or Tri-clover clamp & Gasket

Available in 1″, 1.5″ & 2″ size

Advantages of Diaphragm Seal Pressure Gauges

Diaphragm Seal acts as a barrier between gauge internals and process media, hence, it protects the Internals of pressure Gauges from damage, which is the basic principle of Diaphragm Seal unit. 

With Diaphragm Seal, we can protect the internal of Pressure gauge from Corrosive fluids and other fluids which are harmful for the internals of pressure gauges.

Use of Diaphragm Seal Pressure Gauges increase the durability and longevity of the gauge, if wetted parts are selected, which is compatible to process fluid.

Use Diaphragm Seal provide the safety of Equipment including personnel handling the gauge and that too without affecting the accuracy of Pressure Gauges.

Maintenance of Diaphragm Seal Pressure Gauges is minimal and if we properly select the construction, we can save time and efforts in maintenance.

Consideration While Using Diaphragm Seal Pressure Gauges

It is important that we are selecting the right Diaphragm Seal Pressure Gauges depending upon where we are using the gauge.  There are few points, that need to be considered while selecting the Diaphragm Seal Pressure Gauges, which are:

Pressure Range

We need to ensure that the Pressure range of gauge is suitably selected depending upon the operating and design pressure conditions. 

Temperature Range

We have to consider the temperature involved in the process and have to ensure that the sealing fluid is selected to withstand the temperature of the process.

Material Compatibility

It is important to choose the right material of wetted Parts i.e., parts which are coming in contact with process fluid.  Mainly wetted parts in the Diaphragm Seal Pressure Gauges are its diaphragm and Process Connection.   It is important to which material is suitable and compatible with our process fluid. 

Since, Diaphragm seal is barrier between gauge and process, it should not happen that process fluid is damaging our wetted parts also, otherwise the purpose of using the diaphragm seal unit with the gauge will fail.

Selection of the Process Connection

We have to ensure that the process connection is suitable for the range selected by us.  Specially in case of flanged process connection, we have to ensure that the flange rating is suitable for the pressure and temperature applicable in the process.

We have to understand that for different range spans, size of diaphragm may be different, hence, while selecting the construction, where diaphragm is welded on the RF portion of process flange, size of diaphragm is not exceeding the RF portion of the flange. 

For example, if we use range of 0 to 4 Kg/Cm2, Diaphragm dia is approx. 63mm and if we are using Flange Connection of size 1”, RF dia will be less than 63mm, hence, it is not possible to weld diaphragm on RF portion. 

In such cases, we have to either change the construction of the seal or have to change the size of the flange.

Type of Seal to be used

Different type of Diaphragm Seals is available depending upon the various factors like pressure, temperature, viscosity, process fluid, application, behavior of process fluid at different temperatures, properties of the process fluid etc., hence, it is important to use the right type of seal for your applications.

We have to select the Diaphragm seal, which require minimum and easy maintenance.

Mounting Position

We need to analyses the position of the Diaphragm Seal Pressure Gauges because sometimes it is not possible to mount the gauge due to space constraint.  Sometimes even we have space to mount the gauge, it is not possible for the operator to note the readings.  In such case, we need to select the remote mounted diaphragm seal.

In remote mounted diaphragm seals, Seal is directly mounted on the process tapping and gauge is mounted remotely with the help of capillary.   Length of capillary can be provided as per customers requirement; however, it is recommended to select the same suitably so that response time is not compromised.

Cleaning & Maintenance

It is important to understand that cleaning of diaphragm seal is part of maintenance and depending upon the properties of the process fluid or requirement of the process.

For example, if we have to use the Gauge in Food or Pharmaceutical industry, where batch processing is considered and we require sterilization of the complete system after each batch, then we have to select the Hygiene Pressure Gauges with SMS Fitting or Tri-Clover connection or IDF Fitting.  If we are using fluids those precipitates, we need to select Flush diaphragm type and if fluid is thick enough, we need to select inline flow through type and so on.

Conclusion

Diaphragm Seal Pressure Gauges are vital and indispensable tools in various industries, providing accurate pressure measurement while safeguarding instruments from harsh conditions. Their versatility extends from chemical processing to oil and gas and water treatment, ensuring operational efficiency and safety.

Diaphragm seal’s protective properties against corrosion, abrasion, temperature extremes, and high pressures make them indispensable in modern industrial processes, enabling remote monitoring and enhancing safety.