Technical information

Selection, installation, handling and operationof pressure gauges
WIKA data sheet IN 00.05

General information
The user must ensure that the appropriate pressure gauge
has been selected in terms of scale range and design.
The scale range is optimally selected when the operatingpressure lies in the middle third of the scale range.

Safety levels for cases per EN 837■ “S1” with blow-out device in case back■ “S2” for NS 40 ... NS 80 with blow-out device in case backor blow-out back■ “S3” for NS 40 ... NS 250 with solid baffle wall (Solidfront) and blow-out back 

Exploded diagram of safety level “S3”

The pressure gauge must be mounted free from vibrationand should be aligned so that it is easy to read.
The process connection must be sealed properly.
For zero point checking or the exchange of the instrument
during operation, the installation of a shut-off device between
pressure tapping and pressure gauge is recommended.

Case designs
For operational safety and the protection of personnel who
find themselves in the vicinity of the measuring location, theEN 837-2 user standard requires different safety levels forcases.

WIKA data sheet IN 00.05 ∙ 11/2020

For non-hazardous, liquid media < 25 bar without case filling,no safety level is required. For gaseous or vaporous media
from an operating pressure of 25 bar, in accordance withEN 837-2, a pressure gauge with safety level “S3” is recommended. Furthermore, in accordance with EN 837-2, further
criteria are specified for the selection of the appropriate
safety level for specific fields of application and instrumentversions.

Instrument fixing
If the line to the instrument is not rigid enough for a vibration-free installation, the gauge should be mounted by meansof appropriate fastening elements for wall or pipe mounting if necessary, through the insertion of a capillary.

Measuring system dampening
If vibrations cannot be avoided by means of suitable installation, instruments with a liquid case filling should be used.

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Shut-off devices
Depending on the intended use, stopcocks or shut-off valves
are fitted upstream of the pressure gauge.
Stopcock and shut-off valve
Stopcocks have up to 4 functions:
The supply line is shut and the pressure
element is connected to the atmosphere. The
zero point can be checked.
■ Operation The supply line is open, the pressure element
is pressurised.
■ Blow out
The supply line is open, the medium escapes
into the atmosphere.
■ Testing
The supply line is open and, in addition tothe working pressure gauge, a test pressuregauge can be installed if a test connection isavailable.
■ VentShut-off valves with or without test connection in accordancewith DIN 16270 or DIN 16271 have a vent screw between
the valve seat and instrument connection. If the vent screw isloosened, the venting can be controlled through the thread.
In specific applications (e.g. steam boilers) the shut-off devices must have a test connection, so that the pressure gauge
can be tested without being dismounted. With shut-off valvesin accordance with DIN 16272, the test connection can beisolated separately. In the process industry, the block-andbleed valve is used for this functionality.
Due to their one-piece design, monoflanges can withstandhigh overpressures. Through this, the robust and compact
mounting of the measuring instrument directly to the processflange is possible.

Temperature load
When mounting the pressure gauge it must be ensured that,taking into consideration the influence of convection andheat radiation, no deviation above or below the permissible
ambient and media temperatures can occur. Thus the instrument and the shut-off device must be protected by sufficiently long measuring lines or syphons. The influence of temperature on the indication accuracy must be observed.

Diaphragm seals/Separators
In the case of aggressive, hot, highly viscous, contaminatedor crystallising media, which must not penetrate into thepressure element, diaphragm seals must be provided asseparators.

WIKA data sheet IN 00.05 ∙ 11/2020

To transmit the pressure to the pressure element, a neutral
system fill fluid is used, which must be selected to correspond to the measuring range, temperature and compatibility
with the medium. The connection between instrument anddiaphragm seal must not be disconnected under any circumstances.

Protection of the pressure elements fromoverpressure
If the medium is subject to rapid changes in pressure, orpressure surges are expected, then these must not actdirectly on the pressure element. The action of the pressure
surges must be dampened, for example with the fitting of athrottle section (reduction in cross-section in the pressureport) or through the addition of an adjustable snubber.
If, to favour a higher display resolution, the measuring range
selected is smaller than the maximum pressures that occur
for short times, the pressure element must be protectedagainst damage. For this purpose, an overpressure protector must be connected upstream (external protection); thiscloses immediately in the event of a pressure surge, and only
gradually if the pressure rises slowly. The closing pressure
to be set thus depends on the pressure profile over time. A
further possibility is the use of a pressure gauge with highoverload safety (internal protection).

Pressure tapping
The pressure tapping should be arranged with as large abore as possible (≥ 6 mm) via a shut-off device, so that thepressure tap is not distorted by any flow in the medium.
The measuring line between the pressure tapping and thepressure gauge should have a large enough inner diameter and no sharp bends to prevent blockage and lag in thepressure transmission. Its installation with a steady slope ofapprox. 1:15 is recommended.

Measuring line
The measuring line should be designed and installed so thatthe loads occurring due to expansion, vibration and thermal
effects can be absorbed.
With gaseous media, a drain should be provided at thelowest point; with liquid media, a vent should be provided at
the highest point.
For particle-laden gases or liquids, separators must beprovided which can be isolated from the plant during operation, using shut-off devices, and emptied. If the instrument
needs to be mounted either higher or lower than the pressure
tapping, the measuring range shifts if the medium in themeasuring line does not have the same density as theambient air.

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The shift, ∆p, is derived from the density difference (ρM - ρL)and the height difference, ∆h, in accordance with the formula:∆p = (ρM - ρL) • g • ∆h • 10-5 (bar)

Shift in the measuring range

ρM = Density of the medium (kg/m³)
ρL = Density of the ambient air (kg/m³)(1.205 kg/m³ at 20 °C)∆h = Height difference (m)g=Gravitational acceleration (m/s²)(average gravitational acceleration = 9.81 m/s²)

The display decreases by ∆p, if the pressure gauge is higher;
it increases by ∆p, if the pressure measuring instrument islower than the pressure tapping.
Usually, a pressure gauge is mounted with its dial vertical.
With any deviation, the position indicator on the dial must beobserved.

For process connections with parallel threads, use flatgaskets, lens-type sealing rings or WIKA profile sealings atthe sealing face . The tightening torque is dependent upon
the process connection, the material and the sealing. With
tapered threads (e.g. NPT threads), sealing is made in thethreads,  using a suitable sealing material (EN 837-2).
Parallel and tapered thread connection

Sealing face 

Sealing inthread In order to orientate the instrument so that it can be read aswell as possible, a connection with LH-RH union or union nut
should be used.
When screwing the instruments in, the force required forsealing must not be applied through the case, but onlythrough the spanner flats provided for this purpose, andusing a suitable tool.
If the instrument is located below the pressure tapping, themeasuring line must be flushed thoroughly before installation
to remove any foreign bodies.
Some instrument models have a vent valve with the inscription CLOSE and OPEN for internal pressure compensation.
In the condition at time of supply, this vent valve is closed(lever to setting CLOSE). Before checking and/or after installation and before commissioning, these instruments must bevented, i.e. the lever set to OPEN.

WIKA data sheet IN 00.05 ∙ 11/2020Before the dismounting of a pressure gauge, it must beensured that it is no longer pressurised. If necessary, themeasuring line must have strain relief.
For diaphragm pressure gauges, the clamping bolts of theupper and lower flange must not be loosened.
Liquid media with the property of changing the volume duringsolidification can damage the measuring system (e.g. water if
it falls below the freezing point).
Residual media in dismounted pressure gauges can result ina risk to persons, the environment and equipment. Sufficient
precautionary measures must be taken.

Operation
In order to prevent any pressure surges, shut-off devices
must only be opened slowly.

Mounting and commissioning

Spanner flats

When pressure testing or blowing through pipes or vessels,
the pressure gauge must not be subjected to a higher load
than indicated by the identifying mark ▼ on the dial (EN837-1 and EN 837-3). Otherwise the pressure gauge must
either be protected by a shut-off device or dismounted.

The maximum pressure for static load is indicated by theidentifying mark ▼ on the dial (EN 837-1 and EN 837-3).
Lower values apply for alternating loads.
For a zero point check during operation, the shut-off device
must be closed and the pressure element vented. The pointermust then be within the range marked h at the zero point.
If the pointer is outside the transverse bar, it can generally be assumed that the pressure element is permanently
deformed, which would have to be subjected to closer
inspection in order to avoid measuring errors or accidents.
To check the display during operation, the pressure gaugemust be separated from the process, via the shut-off device
with test connection, and loaded with a test pressure. For
instruments in accordance with EN 837-1 and EN 837-3, thepermissible error limits are defined.
Improper handling with hazardous media, such as, forexample, oxygen, acetylene, flammable or toxic substances, as well as in refrigeration systems, compressors etc.,
can cause dangerous or harmful media to escape into theenvironment, which can lead to damage or injury. For these
media, in addition to all standard regulations, the appropriate
existing codes or regulations must also be followed.

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Storage

Reference documents

To avoid damage, the following points must be observed
when storing the pressure gauges until installation:

Quoted standards■ Leave the instruments in their original packaging and store

them protected from damage by external influences.

■ Following any possible removal of the instruments, e.g.

for testing, the instrument should again be stored in its
original packaging.

■ Storage temperature range: -40 ... +70 °C

Deviating storage temperatures are possible. The permissible temperature range can be taken from the respective
data sheet.

■ Protect the instruments from moisture and dust.

EN 837-1
Bourdon tube pressure gauges - part 1:
Dimensions, metrology, requirements and testing
EN 837-2
Pressure gauges - part 2:
Selection and installation recommendations for pressuregaugesEN 837-3
Diaphragm and capsule pressure gauges - part 3:
Dimensions, metrology, requirements and testing
DIN 16270
PN 250 and PN 400 valves without test connection forpressure gauges
DIN 16271
PN 250 and PN 400 valves with test connection for pressuregaugesDIN 16272
PN 250 and PN 400 valves with blocking test connection forpressure gauges

Shut-off devices

Stopcock

Shut-off valve

Block-and-bleed valve

WIKA data sheet IN 00.05 ∙ 11/2020

Shut-off valve with separately
isolatable test connection

Double-block-and-bleed valve
manifold

Needle valve with ventconnection

Monoflange

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Mounting accessories

LH-RH union

Adjustable snubber

Syphon, compact form

Syphon, trumpet form

Adapter piece for instrument
mounting bracket

Instrument mounting bracket

Syphon, U-form

Overpressure protector

Measuring arrangement
Proven measuring assemblies for various types of media.
Filling of themeasuring line

ExamplesLiquid media

LiquidCondensate

Liquid withvapour

Boiling liquids

Completelyvapourised“Liquid gases”

Gaseous media

GaseousDry air

Partially condensed (damp)

Moist airFlue gases

Completely
condensed

SteamPressure gauge
above the pressure
tapping

Pressure gauge
below the pressure
tapping

11/2020 EN© 09/2010 WIKA Alexander Wiegand SE & Co. KG, all rights reserved.
The specifications given in this document represent the state of engineering at the time of publishing.
We reserve the right to make modifications to the specifications and materials.

WIKA data sheet IN 00.05 ∙ 11/2020

Page 5 of 5WIKA Alexander Wiegand SE & Co. KG
Alexander-Wiegand-Straße 30
63911 Klingenberg/GermanyTel.
+49 9372 132-0
Fax+49 9372 132-406
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