Technical information

Diaphragm seal systems for vacuum processes
WIKA data sheet IN 00.25

VacuumThe word vacuum (from the Latin: vacuus - empty) means“(largely) empty or free space”.
Physics refers to a space that is completely free frommolecules as a vacuum. In practice, this condition is neverfeasible.

Diaphragm seals
Diaphragm seals are used for pressure measurements when
the process medium should not come into contact with thepressurised parts of the measuring instrument.
A diaphragm seal has two primary tasks:
1. Separation of the measuring instrument from the process
medium
2. Hydraulic transfer of the pressure to the measuring
instrument(see also Technical information IN 00.06 “Diaphragm seals- Diaphragm seal systems, application, operating principle,designs”)

Differential pressure transmitter connected to twoflange-type diaphragm seals via a capillary

Absolute pressure
Absolute pressure refers to the perfect vacuum. In thisabsolutely molecule-free space the zero point of the absolutepressure is defined. An example of a common “absolute”
indicated value is the air pressure.
For the required differentiation from other types of pressure,
it is denoted with the index “abs.”, which is derived from theLatin “absolutus”, meaning detached or independent.

Diaphragm seal systems in vacuum
service
For application in vacuum, there are different diaphragm seal
system fill fluids (KN 2, KN 17, KN 21, KN 32, KN 59 andKN 92) used. Each reacts differently in vacuum applications.
In terms of physics, the boiling point temperature of a liquid
decreases with falling pressure.
WIKA data sheet IN 00.25 ∙ 08/2015

In a liquid, at a temperature of greater than 0 K, the particles
attempt to leave the liquid bond (transition from liquid togaseous).
The vapour pressure increases with increasing temperatureand is dependent on the substance or mixture present.
Thus the operating limits for the individual measuringassemblies drop with a process pressure < 1 bar abs. WIKA
has developed three manufacturing processes for this (Basic,Advanced and Premium), which are described below.
This technical information should assist in assessing thelimits of the measuring instruments.
Page 1 of 6

Vacuum in the process industry

This occurs in two steps:
Initially, the easily evaporated substances can be separated
at “normal” pressure (≥ 1,013 mbar abs.). In a second step,
the hard-to-evaporate substances are distilled in a vacuum(< 1,013 mbar abs.). In a vacuum, the boiling point of
individual compounds can be lowered significantly without
destroying them through too high temperatures.
The temperature increases during the course of the process,while the pressure decreases.

etransit

ionVapour pressure

Phas

In the meantime, vacuum processes have establishedthemselves in many industrial and biotechnology plants.
Many processes are no longer conceivable without vacuum
processes. An example for a vacuum process in an industrial
operation is a distillation column or rectification column incrude oil production.
Crude oil is the base. It is introduced to the process, and theproducts are then distilled from it separately according to theindividual boiling point ranges (also known as fractions). The
products are then subjected to further processing.

Gas
LiquidIllustration of the vapour pressure of liquid particles attheir transition to the gaseous phase

Diaphragm seal systems in vacuum service
The following basically applies: The higher the temperatureand the smaller the corresponding process pressure, themore difficult it is to design a functioning measuring assembly.
In terms of physics, there are different types of vacuum. Fromlow vacuum, fine vacuum, high vacuum through to ultra-highvacuum. The process pressure in industrial plant is generally≥ 5 mbar abs. (low vacuum range).

Below, the vacuum processes available from WIKA aredescribed in more detail. The processes basically dependon the minimum process pressure at maximum temperatureand the individual system fill fluids. This technical information
applies for electronic process and industrial transmitters.

Applicable core factors for the required design of a functioning measuring assembly are given in the following points:
Influence quantities for the application process:■■ Process temperature■■ Process pressure

Influence quantities of the diaphragm seal system:■■ Production process of the diaphragm seal system■■ Vapour pressure curve of the selected system fill fluid■■ The selected process connection with the corresponding

diaphragm diameter

Page 2 of 6

WIKA data sheet IN 00.25 ∙ 08/2015

Section  Basic service

Section  Premium service

Through ongoing and continuous advancements in WIKA’svacuum production processes, measuring ranges, for which
specific conditioning of components is no longer necessary,are possible.
The basic service will be designated in the following illustration by section no.  “Basic service”.

For measuring points in lower vacuum ranges and/or withhigh process temperatures, the “Advanced service” is nolonger sufficient.
For this, WIKA has developed the “Premium service” withspecifically designed component conditioning and a refinement of the system fill fluid. The “Premium service” is designated in the illustration with the section no. .

Section  Advanced service

Section  Customer support

For the more-demanding measuring points, WIKA has
established the advanced service. The majority of all measuring assemblies which are intended for use in vacuum can becovered by the advanced service.
The illustration of this service will be designated below insection no.  with “Advanced service”.

If the application finds itself in section no.  “Customersupport”, our technical clarification will work out a solution
for your application.
For this, precise information on the application process isrequired. For this reason, simply fill out this questionnaireand send it to your contact person at WIKA.
Questionnaire for diaphragm seals
http://de-de.wika.de/upload/DS_QuestionnaireDS_GB_5796.pdf

Explanation of the vacuum processes

Our vacuum processes are clearly illustrated in the following diagrams.

Vacuum application with system fill fluid KN 32
1000

Absolute pressure in mbar abs.

50010050


10-100

0Legend Basic Service Advanced Service Premium Service Customer Support
 Functioning diaphragm seal measurement
assemblies not possible in this range

WIKA data sheet IN 00.25 ∙ 08/2015

100


200

Process temperature in °C


300

400

Limit values process temperature
MinimumMaximum

Page 3 of 6

Vacuum application with system fill fluid KN 2
1000

Absolute pressure in mbar abs.

500

10050


10-100



0


100

Legend Basic Service Advanced Service Premium Service Customer Support
 Functioning diaphragm seal measurement
assemblies not possible in this range



200
Process temperature in °C

300

400

Limit values process temperature
Minimum
Maximum

Vacuum application with system fill fluid KN 17
1000

Absolute pressure in mbar abs.

500

10050


10-100Legend
 Basic Service
 Premium ServicePage 4 of 6


0
100

 Advanced Service
 Customer Support
200
Process temperature in °C

300

400

Limit values process temperature
Minimum
Maximum

WIKA data sheet IN 00.25 ∙ 08/2015

Vacuum application with system fill fluid KN 21
1000

Absolute pressure in mbar abs.

500

10050


10-100

0Legend Basic Service
 Premium Service

100

200
Process temperature in °C

 Advanced Service
 Customer SupportOxygen applications
Per BAM test (Federal Institute for Materials Research andTesting) these table values apply.

300

400

Limit values process temperature
Minimum
Maximum

Maximum temperature
to 60 °C
> 60 °C to 100 °C> 100 °C to 175 °C

Maximum oxygen pressure
50 bar
30 bar
25 barVacuum application with system fill fluid KN 59
1000

Absolute pressure in mbar abs.

500

10050
10

-1000Legend
 Basic Service Advanced Service
 Premium Service Customer Support
 Functioning diaphragm seal measurement
assemblies not possible in this range

WIKA data sheet IN 00.25 ∙ 08/2015

100200
Process temperature in °C

300400Limit values process temperature
Minimum
Maximum

Page 5 of 6

Vacuum application with system fill fluid KN 92
1000

Absolute pressure in mbar abs.

500

10050


10




-1000Legend
 Basic Service
 Advanced Service
 Premium Service
 Customer Support
 Functioning diaphragm seal measurement
assemblies not possible in this range

100200

Process temperature in °C

300

400

Limit values process temperature
Minimum
Maximum© 2014 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.

Page 6 of 608/2015 ENWIKA data sheet IN 00.25 ∙ 08/2015

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.de
www.wika.de