G1/4 EN 837 or G1/4 DIN 3852: Correctly Distinguishing the Sealing Principle on Pressure Gauges

→ Product category: Pressure measuring technology

 

A pressure gauge is marked:

G 1/4

and the existing connection on the machine also has a G 1/4 thread. The measuring instrument should therefore fit. However, when it is screwed in, the seal does not seat correctly, the pressure gauge bottoms out too early or the connection remains leaky despite being tightened firmly.

The reason: G 1/4 alone does not fully define the process connection. Two connections can have the same thread size and still use different sealing surfaces, screw-in geometries and sealing systems.

In pressure measurement technology, the following are particularly often confused:

G 1/4 B according to EN 837

and:

G 1/4 according to DIN 3852-E or DIN EN ISO 1179-2

.

With the conventional pressure gauge connection according to EN 837, sealing is usually achieved using a separate seal on a designated sealing surface in front of the thread. With Form E according to DIN 3852, or today DIN EN ISO 1179-2, which is widely used in hydraulics, a defined elastomer profile seal is located in the area of the screw-in stud or its contact surface.

The fact that two G 1/4 connections can be screwed together does not necessarily mean that they form a technically correct and permanently leak-tight connection.

ICS Schneider offers numerous solutions with different process connections under Pressure Measurement Technology. A useful example is the IMP17.600 G Pressure Transmitter, which is available, among other options, with G1/4 DIN 3852 with FKM seal or alternatively with G1/4 EN 837.

Why G 1/4 alone does not clearly define the connection

The designation:

G 1/4

initially describes the thread size.

However, additional information is required for a complete mechanical connection.

In practice, the following must also be known

• which connection standard or connection form is used,
• where the sealing takes place,
• which seal is used,
• which mating port is required,
• how deeply the connection may or must be screwed in.

Therefore, for example:

G 1/4 EN 837

G 1/4 DIN 3852-E

G 1/4 DIN 3852-A

and other G 1/4 connection variants cannot simply be regarded as identical.

The thread is only one part of the connection

With these parallel-thread connections, the actual sealing effect is not created by the thread flanks wedging against each other.

The designated sealing point is decisive.

What does G 1/4 mean?

The “G” designates a parallel pipe thread.

Unlike a tapered connection, the thread diameter does not intentionally change along the engagement length in order to create a seal.

This has an important consequence

The thread essentially provides the:

• mechanical connection,
• axial preload of the seal.

The actual sealing takes place at a separate defined point.

This clearly differs from a tapered connection such as:

1/4 NPT

or:

R 1/4

where sealing takes place in the thread area.

Direct comparison of G1/4 EN 837 and DIN 3852-E

Feature	G1/4 EN 837	G1/4 DIN 3852-E / ISO 1179-2
Typical application	Pressure gauges and conventional pressure measurement technology	Hydraulics, mechanical engineering, pressure sensors
Thread	Parallel G thread	Parallel G thread
Sealing principle	Seal on a defined sealing surface in front of the thread	Soft seal / profile sealing ring on a defined contact surface of the screw-in stud
Typical seal	Copper, stainless steel or suitable profile seal	Elastomer or ED profile seal
Typical mating connection	Port designed for an EN 837 connection	Screw-in port according to ISO 1179-1
Common application	Bourdon tube pressure gauges	Pressure transmitters and hydraulic components
Freely interchangeable?	No – the sealing geometry must match the mating connection

How G1/4 EN 837 seals

The conventional G1/4 connection according to EN 837 originates from pressure gauge technology.

WIKA describes sealing for this connection as taking place:

in front of the thread

on the designated sealing surface.

Typical seals include, for example

• copper sealing rings,
• stainless steel sealing rings,
• suitable profile seals,
• other suitable flat seals intended for the connection, depending on the application.

The connection may also have a centering geometry that positions appropriately designed seals in a defined manner.

The mating part must take this design into account

With an EN 837 connection, therefore, just any:

G1/4 female thread

is not sufficient.

The geometry of the port must also provide the intended sealing seat.

Particularly important

The thread itself is not the primary sealing point in this design.

Using PTFE tape on the thread therefore does not replace the correct sealing surface.

How G1/4 DIN 3852-E seals

G1/4 according to DIN 3852-E is more strongly associated with hydraulics and mechanical engineering.

With Form E, a defined contact geometry for a soft seal is located behind or at the end of the threaded section.

The seal is axially compressed when the fitting is tightened

Typical examples are so-called:

ED seals

or:

profile sealing rings

made of an elastomeric material.

Depending on the instrument and process conditions, materials such as:

• NBR,
• FKM,
• EPDM

may be used.

Advantage of this system

The seal is geometrically positioned in a clearly defined location on the screw-in stud.

With the correct mating port, it is compressed in a controlled manner between the connection and the mating surface during tightening.

The same applies here

The parallel G thread does not seal through its thread flanks.

The soft seal provides the sealing function.

DIN 3852-E or DIN EN ISO 1179-2?

Technical data sheets and older plant documentation often still use the designation:

DIN 3852-E

For parallel G pipe threads, reference is now often made to:

DIN EN ISO 1179-2

.

This is why both designations can appear in technical documentation

WIKA, for example, uses the description:

DIN EN ISO 1179-2, formerly DIN 3852-E

.

When sourcing a replacement, it is therefore useful not to search only for the old standard designation, but also to compare the current connection specification and dimensional drawing.

Why “G1/4 DIN 3852” alone is also not unambiguous

The designation:

G1/4 DIN 3852

is also not fully unambiguous without specifying the form.

Different sealing principles exist within this connection family.

Examples include

• Form A with a separate sealing washer,
• Form B with a metallic sealing principle,
• Form E with an elastomeric profile seal.

In addition, modern ISO versions with O-ring sealing also exist.

Therefore, an order should ideally specify

G1/4 DIN EN ISO 1179-2 Form E

or the complete connection designation used by the manufacturer.

“G1/4” or “G1/4 DIN 3852” alone may not provide enough information for unambiguous replacement procurement.

Are EN 837 and DIN 3852-E compatible with each other?

This is one of the most frequently asked questions.

The short answer is

Not automatically.

Although the threads have the same nominal size, the intended sealing points are different.

This can result in a situation where

• the male thread initially engages without difficulty,
• several thread turns can be screwed in,
• but the intended seal does not reach the correct mating surface.

The result can be a connection that initially appears mechanically compatible but is not technically sealed correctly.

Particularly problematic

is the attempt to make an unsuitable combination leak-tight simply by using:

• a higher tightening torque,
• additional sealing washers,
• PTFE tape,
• liquid thread sealant.

This does not correct the actual geometry of the connection.

Why screw-in depth and connection geometry are important

When evaluating a connection, comparing only the external thread is not sufficient.

The following dimensions are also relevant:

• length of the threaded stud,
• position of the sealing surface,
• outside diameter of the contact surface,
• geometry of the centering area,
• depth of the mating port.

Incorrect geometry can cause

the connection to bottom out mechanically before the seal has been compressed sufficiently.

Conversely, a seal can be excessively deformed if the mating connection does not match the intended connection form.

Therefore, with unknown connections

the thread should not only be identified using a thread gauge.

A dimensional drawing of the existing connection is also useful.

Which seal belongs to which connection?

Connection	Typical sealing principle	Typical seal
G1/4 EN 837	Axial sealing surface at the connection	Copper, stainless steel or suitable profile seal
G1/4 ISO 1179-2 / DIN 3852-E	Axially compressed soft seal on the screw-in stud	ED/profile seal, e.g. NBR or FKM
G1/4 DIN 3852-A	Separate sealing washer	Standard-compliant sealing washer
G1/4 ISO 1179-3	O-ring sealing	O-ring with designated retaining geometry
1/4 NPT	Sealing in the tapered thread	Suitable thread sealant

The table shows why the term:

G1/4 seal

alone is also insufficient.

The seal must always match the connection form.

Do not confuse an O-ring with a Form E seal

In everyday language, elastomer seals are often generally referred to as:

O-rings

.

Technically, this is not always correct.

The conventional Form E according to ISO 1179-2

uses a dedicated elastomer seal or profile seal.

A conventional round O-ring, on the other hand, belongs to other connection forms, for example certain connections according to ISO 1179-3.

Why this distinction is important

An arbitrary O-ring with an approximately suitable diameter is not a substitute for a defined Form E seal.

Cross-section, material and sealing geometry must match the groove and the mating surface.

PTFE tape and thread sealant on G threads

A common reaction to a leaking G1/4 connection is:

We will simply put PTFE tape on the thread.

For EN 837 and DIN 3852-E, this is generally not the intended sealing principle

With parallel-thread connections, sealing is achieved via the designated sealing surface or seal.

WIKA explicitly distinguishes between:

parallel thread → sealing at the sealing surface

and:

tapered thread → sealing in the thread

PTFE tape is therefore not a substitute for

• a missing copper sealing ring,
• a damaged Form E seal,
• an incorrect mating port,
• an unsuitable adapter.

In addition, excessive sealing material can enter the pressure channel and interfere with small bores or measuring passages.

Selecting the correct adapter

If an existing pressure gauge and process connection use different connection forms, a suitable adapter is often the cleanest solution.

A correct adapter must be fully defined on both sides

For example:

Instrument side: female connection for G1/4 EN 837

Process side: G1/4 ISO 1179-2 Form E

The designation

G1/4 to G1/4 adapter

is not sufficient.

After all, the purpose of the adapter is precisely to connect two different connection and sealing geometries.

The following must also be suitable for the adapter

• permissible operating pressure,
• material,
• sealing material,
• temperature range,
• medium.

Installing a pressure gauge correctly

Even a fully compatible process connection can be damaged by incorrect installation.

The pressure gauge must not be screwed in using the housing

Only the designated:

wrench flat on the process connection

should be used for tightening.

If the entire housing is used as a lever, the:

• connection,
• measuring system,
• housing connection

can be mechanically stressed.

Before installation, the

• sealing surface,
• thread,
• seal,
• mating connection

should be clean and undamaged.

When screwing in

the thread must not be cross-threaded.

The final tightening torque depends on:

• connection geometry,
• type of seal,
• sealing material,
• material of the mating connection.

A general rule such as:

Always tighten G1/4 to X Nm

is therefore not appropriate.

Aligning the pressure gauge correctly after installation

An analogue pressure gauge must be easy to read after installation.

With a parallel thread, however, the instrument cannot simply be turned further once the seal has been correctly compressed.

The pressure gauge should therefore not

be forcibly turned another:

half turn

after the correct sealing compression has been reached simply to make the dial face straight.

For freely adjustable positioning

depending on the installation, for example:

• clamping sockets,
• union nuts,
• suitable pressure gauge connectors,
• appropriate adapters

can be used.

This allows the sealing function and alignment to be separated from each other.

Selecting the sealing material to suit the medium

With soft-sealing connections, not only the geometry must be correct.

The sealing material must also be compatible with the process medium.

Typical elastomer materials include

• NBR,
• FKM,
• EPDM.

These materials have different properties with regard to:

• mineral oils,
• fuels,
• water,
• steam,
• chemicals,
• temperature.

Therefore

“G1/4 DIN 3852-E” defines the mechanical connection form – it does not automatically define the correct sealing material for the medium.

Considering temperature when selecting the seal

Temperature particularly affects elastomer seals.

A material may, for example, be chemically suitable for the medium but operated outside its permissible temperature range.

Possible consequences include

• hardening,
• swelling,
• permanent deformation,
• embrittlement,
• leakage.

At high process temperatures, a metal-sealing connection solution or a sealing material suitable for the required temperature may therefore be advantageous.

Considering pressure rating and mechanical load

The fact that a connection can be mechanically screwed in does not automatically mean that it is suitable for the existing pressure.

The following must be considered:

• permissible operating pressure of the measuring instrument,
• permissible pressure of the adapter,
• pressure resistance of the mating connection,
• seal,
• temperature.

Especially in hydraulic applications

pressure spikes can occur that are significantly higher than the normal operating pressure.

The process connection is therefore part of the overall pressure-bearing capability of the measuring point.

Special requirements for oxygen

For oxygen applications, checking only the thread and sealing geometry is not sufficient.

In addition, the following must be suitable for oxygen

• materials,
• seals,
• cleanliness condition,
• greases and lubricants,
• permissible pressure.

A connection that is technically suitable for a normal hydraulic application must therefore not automatically be used in an oxygen application.

For such applications, only instruments, seals and installation procedures approved for oxygen service should be used.

Typical error patterns with G1/4 connections

Observation	Possible cause	Recommended check
Thread can be screwed in, but the connection still leaks	Different sealing principles on instrument and mating connection	Check EN 837 or ISO 1179 / DIN 3852 form
Pressure gauge bottoms out mechanically before the seal becomes tight	Incorrect connection geometry or screw-in depth	Compare dimensional drawings
Seal is pushed out strongly	Incorrect seal type or incorrect mating surface	Check seal and connection form
DIN 3852-E connection leaks despite a new seal	Profile seal damaged or mating surface defective	Check sealing surface and seal
EN 837 pressure gauge leaks after replacement	Old sealing ring reused or missing	Install a suitable new seal
PTFE tape seals the connection only temporarily	Incorrect sealing principle is being masked	Identify the correct connection geometry
Pressure gauge is misaligned after tightening	Seal already correctly compressed	Use a clamping socket or suitable connector
G1/4 sensor does not fit the existing G1/4 port	Different connection form despite same thread size	Check complete standard designation and drawing
Elastomer seal starts leaking after a short time	Medium or temperature unsuitable	Check sealing material
Thread is damaged during installation	Cross-threading or wrong thread	Check thread type and condition
Leakage occurs only during pressure spikes	Seal or adapter not suitably rated	Check maximum pressure and dynamic loading
Measuring instrument was damaged during installation	Installation force applied through the housing	Use wrench flat only

Practical examples

Example 1: G1/4 EN 837 pressure gauge on a hydraulic block

An analogue pressure gauge has:

G1/4 B EN 837

However, the hydraulic block is designed for:

G1/4 ISO 1179-2 Form E

.

What happens?

The thread size initially appears to match.

However, the intended EN 837 sealing surface of the pressure gauge and the Form E mating connection of the hydraulic block do not automatically form the intended sealing pair.

Correct solution

An adapter is used that correctly provides:

EN 837 on the pressure gauge side

and:

ISO 1179-2 Form E on the process side

.

Example 2: DIN 3852-E pressure transmitter replaces a pressure gauge

An existing pressure gauge with:

G1/4 EN 837

is replaced by an electronic pressure sensor.

However, the new sensor was ordered with:

G1/4 DIN 3852-E

.

Typical mistake

It is assumed:

G1/4 = G1/4 → it must fit

The mechanical design and sealing principle were not taken into account.

Better approach

Before ordering the sensor, check:

• the standard of the existing connection,
• the sealing surface,
• the required seal,
• the dimensional drawing.

If possible, the new sensor should be ordered directly with the correct process connection.

Example 3: Leaking connection despite PTFE tape

A G1/4 connection remains leaky.

The male thread is then wrapped several times with PTFE tape.

The problem

The connection was designed to seal at the end or contact surface.

The tape unintentionally moves the sealing function into the thread.

This does not eliminate the actual cause.

Correct check

identify connection form → check correct seal → inspect sealing surface → install correctly

Systematically identifying an existing connection

If the connection type of an existing machine is unknown, it should not be guessed from the thread diameter alone.

1. Identify the thread: Check whether it is actually G1/4 and not, for example, 1/4 NPT or R1/4.
2. Check parallel or tapered: The sealing principle depends fundamentally on this.
3. Inspect the mating surface: Where is the connection designed to seal?
4. Identify the existing seal: Copper ring, profile seal, O-ring or another system.
5. Find the connection drawing: Consult the documentation of the machine or fitting.
6. Measure screw-in depth: If uncertain, compare with the manufacturer’s drawing.
7. Record the standard designation: Clearly document EN 837, ISO 1179-2 or another connection form.
8. Check medium and temperature: Select the sealing material accordingly.
9. Check the pressure range: Ensure that adapter and measuring instrument are adequately rated.
10. Only then select the measuring instrument or adapter.

Selecting the correct process connection

For a new measuring point, the connection should be specified as completely as possible.

Instead of:

Pressure gauge, G1/4 connection

preferably specify, for example:

Pressure gauge, G1/4 B EN 837, bottom connection

or:

Pressure transmitter, G1/4 DIN EN ISO 1179-2 Form E, FKM seal

In addition, the following should be defined

• measuring range,
• pressure type,
• medium,
• temperature,
• material,
• sealing material,
• connection position,
• maximum operating pressure.

This prevents an otherwise technically suitable measuring instrument from being impossible to install because of an apparently minor connection detail.

Suitable pressure measurement technology from ICS Schneider

IMP17.600 G Pressure Transmitter

The IMP17.600 G clearly demonstrates why the full connection designation is important.

ICS offers it, among other options, with:

• G1/4 DIN 3852 with FKM seal,
• G1/4 EN 837,
• 1/4 NPT,
• G1/2 EN 837

.

This means that different mechanical connection and sealing concepts can already be selected for the same pressure transmitter.

IMP17.620 G

The IMP17.620 G is also available with G1/4 DIN 3852 and has a defined seal at the pressure connection.

Pressure Measurement Technology

Further:

• pressure gauges,
• digital pressure gauges,
• pressure sensors,
• pressure transmitters,
• pressure switches,
• accessories and adapters

can be found under Pressure Measurement Technology at ICS Schneider.

Conclusion

G1/4 EN 837 and G1/4 DIN 3852-E have the same nominal thread size, but they are not identical process connections.

G1/4 initially describes only the thread

For a correct connection, the sealing principle and connection geometry must also be known.

EN 837 is typically associated with pressure gauge technology

Sealing takes place via a designated sealing surface with a suitable separate seal.

DIN 3852-E or ISO 1179-2 is widely used in hydraulics

Here, a defined elastomer profile seal is used on the screw-in stud.

A thread that can be screwed in does not prove compatibility

Two G1/4 components can mechanically engage with each other and still have an incorrect sealing pair.

PTFE tape does not solve this problem

With parallel-thread connections according to EN 837 and ISO 1179-2, the intended seal must provide the sealing function.

“DIN 3852” should also be specified more precisely

Different forms use different sealing principles. In particular, Form E must not generally be equated with arbitrary O-ring connections.

Adapters must fully account for both connection sides

A “G1/4-to-G1/4 adapter” is not clearly defined without specifying the sealing geometry on each side.

For practical applications

Determine the thread size → identify the complete connection standard → identify the sealing principle → check mating port and screw-in geometry → select the correct seal → consider material, medium and temperature → correctly specify adapters for different connection forms → install the measuring instrument only using the wrench flat → observe the specified tightening torque → then check the connection for leak tightness.

FAQ: Correctly Distinguishing G1/4 EN 837 and DIN 3852

What is the difference between G1/4 EN 837 and G1/4 DIN 3852?

The thread size is similarly or identically designated, but the sealing surface and sealing principle differ. The connections must therefore not be considered identical based solely on the G1/4 designation.

What does G1/4 mean?

G1/4 designates a parallel pipe thread of the corresponding nominal size. However, the designation does not fully describe the sealing principle of the process connection.

Does a G1/4 thread seal in the thread?

With typical parallel connections according to EN 837 or ISO 1179-2, sealing does not take place at the thread flanks, but at a designated sealing point.

How does G1/4 EN 837 seal?

The connection is usually sealed using a suitable seal on the designated sealing surface in front of the threaded section.

Which seal is used with EN 837?

Depending on the design, copper, stainless steel or suitable profile seals can be used, for example.

How does G1/4 DIN 3852-E seal?

Form E uses a defined soft or profile seal that is compressed against the designated mating surface when the connection is tightened.

Is DIN 3852-E still current?

For corresponding parallel G connections, DIN EN ISO 1179-2 is now frequently specified. However, the older designation DIN 3852-E is still widely used in technical documentation.

Is DIN 3852-E the same as ISO 1179-2?

For corresponding G-thread connections, ISO 1179-2 is used as the successor reference to the former DIN 3852-E version. Nevertheless, the specific manufacturer’s drawing should always be checked for replacement parts.

Can I screw G1/4 EN 837 into G1/4 DIN 3852-E?

The thread may mechanically fit to some extent. However, this does not mean that the intended sealing geometry is compatible. Such a combination should only be used if explicitly intended by the manufacturer or by the connection geometry.

Why does the connection leak despite having the same G1/4 thread?

The cause is often different sealing surfaces or connection forms.

Can I use PTFE tape for G1/4 EN 837?

PTFE tape does not replace the seal on the sealing surface intended for EN 837.

Can I use PTFE tape with DIN 3852-E?

With Form E, the thread is also not intended as the primary sealing point. A damaged or missing profile seal should therefore not be replaced with PTFE tape.

When is PTFE tape typically used?

Thread sealants are typically used with designated tapered threads such as certain NPT or R connections.

Is the DIN 3852-E seal an O-ring?

Not in the strict technical sense. Conventional Form E uses a designated elastomer profile or ED seal. O-ring systems exist in other connection forms.

Can I use a standard O-ring instead of a Form E seal?

No. The seal must be designed for the intended connection in terms of both geometry and material.

What does Form E mean?

Form E designates a defined connection and sealing geometry with a soft-sealing profile ring.

Are there other forms within DIN 3852?

Yes. Different forms with different sealing principles exist or existed, for example Forms A, B and E.

Is the designation “G1/4 DIN 3852” sufficient when ordering?

A complete specification including the form or current ISO standard and seal is preferable.

Why does EN 837 require a different mating connection?

Because the connection has its defined sealing surface at a different geometric position than, for example, a Form E connection.

Can I use an adapter?

Yes. However, the adapter must have the actual connection and sealing form used on both sides.

How should an adapter be specified?

Both sides should be fully defined, for example an EN 837 female connection on the instrument side and an ISO 1179-2 Form E connection on the process side.

Can I use any G1/4-to-G1/4 adapter?

No. Identical thread sizes do not indicate whether the sealing geometries on both sides are suitable for the application.

How can I identify an unknown G1/4 connection?

In addition to the thread, the sealing surface, existing seal, screw-in geometry and, if available, a manufacturer’s drawing should be examined.

Can EN 837 and DIN 3852 be distinguished from the external thread alone?

This may be difficult based solely on the thread flanks. The geometry of the complete screw-in stud and the position of the sealing surface are more important.

Why must I not tighten a pressure gauge by turning the housing?

This can mechanically stress the connection and internal measuring system. The designated wrench flat should be used for tightening.

How tightly should a G1/4 pressure gauge be tightened?

The required tightening torque depends on the connection, seal, material and mating connection. The manufacturer’s specification should therefore be used.

How do I align a pressure gauge after screwing it in?

If the desired position does not coincide with the correct sealing compression, a suitable clamping socket, union nut or pressure gauge connector should be used.

Can a seal be reused?

This depends on the seal type. Deformed, damaged or single-use seals should be replaced.

Which sealing material is suitable for hydraulic oil?

This must be checked based on the specific hydraulic medium, temperature and manufacturer approval. NBR and FKM are common materials, but they are not automatically suitable for every application.

Why is temperature important for DIN 3852-E seals?

Elastomers change their mechanical properties at high or low temperatures. The permissible temperature range of the sealing material must therefore be observed.

Is G1/4 EN 837 typical for pressure gauges?

Yes. The connection originates from conventional pressure gauge technology and is widely used on mechanical pressure measuring instruments.

Is G1/4 DIN 3852-E typical for pressure sensors?

Yes. This connection form is widely used, particularly in hydraulics and mechanical engineering, and is frequently found on electronic pressure sensors and pressure transmitters.

Is there a pressure transmitter from ICS Schneider with both connection variants?

Yes. The IMP17.600 G is available with, among other options, G1/4 DIN 3852 and G1/4 EN 837 as different mechanical connection variants.

Where can I find the IMP17.600 G?

Further information is available under IMP17.600 G at ICS Schneider.

Where can I find further pressure measuring instruments?

An overview is available under Pressure Measurement Technology at ICS Schneider.