Technical information

Selection, installation, handling and operation

of pressure gauges
WIKA data sheet IN 00.05

General information Safety levels for cases per EN 837

■ “S1” with blow-out device in case back
The user must ensure that the appropriate pressure gauge ■ “S2” for NS 40 ... NS 80 with blow-out device in case back
has been selected in terms of scale range and design. or blow-out back
The scale range is optimally selected when the operating ■ “S3” for NS 40 ... NS 250 with solid baffle wall 
pressure lies in the middle third of the scale range. (Solidfront) and blow-out back 
Exploded diagram of safety level “S3”




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 with
EN 837-2, a pressure gauge with safety level “S3” is recom-
mended. Furthermore, in accordance with EN 837-2, further
The pressure gauge must be mounted free from vibration criteria are specified for the selection of the appropriate
and should be aligned so that it is easy to read. safety level for specific fields of application and instrument
versions.
The process connection must be sealed properly.

For zero point checking or the exchange of the instrument Instrument fixing
during operation, the installation of a shut-off device between
pressure tapping and pressure gauge is recommended. If the line to the instrument is not rigid enough for a vibra-
tion-free installation, the gauge should be mounted by means
of appropriate fastening elements for wall or pipe mounting -
Case designs if necessary, through the insertion of a capillary.

For operational safety and the protection of personnel who

find themselves in the vicinity of the measuring location, the Measuring system dampening
EN 837-2 user standard requires different safety levels for
cases. If vibrations cannot be avoided by means of suitable installa-
tion, instruments with a liquid case filling should be used.

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Shut-off devices To transmit the pressure to the pressure element, a neutral
system fill fluid is used, which must be selected to corre-
Depending on the intended use, stopcocks or shut-off valves spond to the measuring range, temperature and compatibility
are fitted upstream of the pressure gauge. with the medium. The connection between instrument and
diaphragm seal must not be disconnected under any circum-
Stopcock and shut-off valve stances.
Stopcocks have up to 4 functions:

■ Vent The supply line is shut and the pressure Protection of the pressure elements from
element is connected to the atmosphere. The overpressure
zero point can be checked.
■ Operation The supply line is open, the pressure element If the medium is subject to rapid changes in pressure, or
is pressurised. pressure surges are expected, then these must not act
■ Blow out The supply line is open, the medium escapes directly on the pressure element. The action of the pressure
into the atmosphere. surges must be dampened, for example with the fitting of a
■ Testing The supply line is open and, in addition to throttle section (reduction in cross-section in the pressure
the working pressure gauge, a test pressure port) or through the addition of an adjustable snubber.
gauge can be installed if a test connection is If, to favour a higher display resolution, the measuring range
available. selected is smaller than the maximum pressures that occur
for short times, the pressure element must be protected
Shut-off valves with or without test connection in accordance against damage. For this purpose, an overpressure protec-
with DIN 16270 or DIN 16271 have a vent screw between tor must be connected upstream (external protection); this
the valve seat and instrument connection. If the vent screw is closes immediately in the event of a pressure surge, and only
loosened, the venting can be controlled through the thread. gradually if the pressure rises slowly. The closing pressure
to be set thus depends on the pressure profile over time. A
In specific applications (e.g. steam boilers) the shut-off devic- further possibility is the use of a pressure gauge with high
es must have a test connection, so that the pressure gauge overload safety (internal protection).
can be tested without being dismounted. With shut-off valves
in accordance with DIN 16272, the test connection can be
isolated separately. In the process industry, the block-and- Pressure tapping
bleed valve is used for this functionality.
The pressure tapping should be arranged with as large a
Due to their one-piece design, monoflanges can withstand bore as possible (≥ 6 mm) via a shut-off device, so that the
high overpressures. Through this, the robust and compact pressure tap is not distorted by any flow in the medium.
mounting of the measuring instrument directly to the process The measuring line between the pressure tapping and the
flange is possible. pressure gauge should have a large enough inner diame-
ter and no sharp bends to prevent blockage and lag in the
pressure transmission. Its installation with a steady slope of
Temperature load approx. 1:15 is recommended.

When mounting the pressure gauge it must be ensured that,

taking into consideration the influence of convection and Measuring line
heat radiation, no deviation above or below the permissible
ambient and media temperatures can occur. Thus the instru- The measuring line should be designed and installed so that
ment and the shut-off device must be protected by sufficient- the loads occurring due to expansion, vibration and thermal
ly long measuring lines or syphons. The influence of tempera- effects can be absorbed.
ture on the indication accuracy must be observed. With gaseous media, a drain should be provided at the
lowest point; with liquid media, a vent should be provided at
the highest point.
Diaphragm seals/Separators
For particle-laden gases or liquids, separators must be
In the case of aggressive, hot, highly viscous, contaminated provided which can be isolated from the plant during opera-
or crystallising media, which must not penetrate into the tion, using shut-off devices, and emptied. If the instrument
pressure element, diaphragm seals must be provided as needs to be mounted either higher or lower than the pressure
separators. tapping, the measuring range shifts if the medium in the
measuring line does not have the same density as the
ambient air.

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The shift, ∆p, is derived from the density difference (ρM - ρL) When pressure testing or blowing through pipes or vessels,
and the height difference, ∆h, in accordance with the formula: the pressure gauge must not be subjected to a higher load
than indicated by the identifying mark ▼ on the dial (EN
∆p = (ρM - ρL) • g • ∆h • 10-5 (bar) 837-1 and EN 837-3). Otherwise the pressure gauge must
Shift in the measuring range either be protected by a shut-off device or dismounted.

ρM = Density of the medium (kg/m³) Before the dismounting of a pressure gauge, it must be
ensured that it is no longer pressurised. If necessary, the
ρL = Density of the ambient air (kg/m³) measuring line must have strain relief.
(1.205 kg/m³ at 20 °C) For diaphragm pressure gauges, the clamping bolts of the
∆h = Height difference (m) upper and lower flange must not be loosened.
Liquid media with the property of changing the volume during
g= Gravitational acceleration (m/s²) solidification can damage the measuring system (e.g. water if
(average gravitational acceleration = 9.81 m/s²) it falls below the freezing point).
The display decreases by ∆p, if the pressure gauge is higher; Residual media in dismounted pressure gauges can result in
it increases by ∆p, if the pressure measuring instrument is a risk to persons, the environment and equipment. Sufficient
lower than the pressure tapping. precautionary measures must be taken.
Usually, a pressure gauge is mounted with its dial vertical.
With any deviation, the position indicator on the dial must be
observed.
Operation
In order to prevent any pressure surges, shut-off devices
must only be opened slowly.
Mounting and commissioning
The maximum pressure for static load is indicated by the
For process connections with parallel threads, use flat
identifying mark ▼ on the dial (EN 837-1 and EN 837-3).
gaskets, lens-type sealing rings or WIKA profile sealings at
Lower values apply for alternating loads.
the sealing face . The tightening torque is dependent upon
the process connection, the material and the sealing. With
For a zero point check during operation, the shut-off device
tapered threads (e.g. NPT threads), sealing is made in the
must be closed and the pressure element vented. The pointer
threads,  using a suitable sealing material (EN 837-2).
must then be within the range marked h at the zero point.
Parallel and tapered thread connection
If the pointer is outside the transverse bar, it can general-
ly be assumed that the pressure element is permanently
deformed, which would have to be subjected to closer
Spanner flats
Sealing in inspection in order to avoid measuring errors or accidents.
thread 
Sealing face 
To check the display during operation, the pressure gauge
In order to orientate the instrument so that it can be read as must be separated from the process, via the shut-off device
well as possible, a connection with LH-RH union or union nut with test connection, and loaded with a test pressure. For
should be used. instruments in accordance with EN 837-1 and EN 837-3, the
When screwing the instruments in, the force required for permissible error limits are defined.
sealing must not be applied through the case, but only
through the spanner flats provided for this purpose, and Improper handling with hazardous media, such as, for
using a suitable tool. example, oxygen, acetylene, flammable or toxic substanc-
es, as well as in refrigeration systems, compressors etc.,
If the instrument is located below the pressure tapping, the can cause dangerous or harmful media to escape into the
measuring line must be flushed thoroughly before installation environment, which can lead to damage or injury. For these
to remove any foreign bodies. media, in addition to all standard regulations, the appropriate
existing codes or regulations must also be followed.
Some instrument models have a vent valve with the inscrip-
tion 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 instal-
lation and before commissioning, these instruments must be
vented, i.e. the lever set to OPEN.

WIKA data sheet IN 00.05 ∙ 11/2020 Page 3 of 5

Storage Reference documents
To avoid damage, the following points must be observed Quoted standards
when storing the pressure gauges until installation:
EN 837-1
■ Leave the instruments in their original packaging and store Bourdon tube pressure gauges - part 1:
them protected from damage by external influences. Dimensions, metrology, requirements and testing

■ Following any possible removal of the instruments, e.g. EN 837-2

for testing, the instrument should again be stored in its Pressure gauges - part 2:
original packaging. Selection and installation recommendations for pressure
gauges
■ Storage temperature range: -40 ... +70 °C
EN 837-3
Deviating storage temperatures are possible. The permis-
Diaphragm and capsule pressure gauges - part 3:
sible temperature range can be taken from the respective
Dimensions, metrology, requirements and testing
data sheet.
DIN 16270
■ Protect the instruments from moisture and dust.
PN 250 and PN 400 valves without test connection for
pressure gauges

DIN 16271
PN 250 and PN 400 valves with test connection for pressure
gauges

DIN 16272
PN 250 and PN 400 valves with blocking test connection for
pressure gauges

Shut-off devices

Stopcock Shut-off valve Shut-off valve with separately Needle valve with vent
isolatable test connection connection

Block-and-bleed valve Double-block-and-bleed valve Monoflange

manifold

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 Mounting accessories

LH-RH union Adjustable snubber Adapter piece for instrument Instrument mounting bracket
mounting bracket

Syphon, compact form Syphon, trumpet form Syphon, U-form Overpressure protector

Measuring arrangement
Proven measuring assemblies for various types of media.
Liquid media Gaseous media
Filling of the Liquid Liquid with Completely Gaseous Partially con- Completely
measuring line vapour vapourised densed (damp) condensed
Examples Condensate Boiling liquids “Liquid gases” Dry air Moist air Steam
Flue gases
Pressure gauge
above the pressure
tapping

Pressure gauge
below the pressure
tapping

© 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.
11/2020 EN

WIKA data sheet IN 00.05 ∙ 11/2020 Page 5 of 5

WIKA Alexander Wiegand SE & Co. KG

Alexander-Wiegand-Straße 30
63911 Klingenberg/Germany
Tel. +49 9372 132-0
Fax +49 9372 132-406
info@wika.com
www.wika.com