General information Steam traps - International standards
7
Local regulations may restrict the use of this product to below the conditions quoted. In the interests of development and improvement of the product, we reserve the right to change the specification without notice. © Copyright 2025
TI-F01-27 CMGT Issue 7
Steam Trap International Standards
With so many steam trap manufacturers displaying a wide range of product information in many different formats it is easy to see why many purchasers and specifiers find the selection of steam traps confusing. Many customers are also under pressure to comply with local and Governmental legislation for their steam systems such as Pressurised Systems Regulations, The Factories Act, Health and Safety Executive and the European Pressure Equipment Directive 2014/68/EU. Misleading product information such as inaccurate condensate capacities are just one of the problems encountered. To make capacity figures appear higher than they really are many manufacturers supply capacities for cold water and claim they are hot water capacities. In practice, hot water capacities are typically 60 - 70% lower than cold water capacities. Products need to be clearly identified so that in the event of any problems the correct supplier can be contacted. It is hard to believe that in todays quality conscious world there are many manufacturers who only mark their products with the pipe size and direction of flow - no manufacturers identification at all. The only safe and professional way to ensure that high quality, system safety and reliability is maintained is to install only products of proven and guaranteed quality. The following National/International standards apply to steam traps and are intended to ensure that any purchaser / specifier has the full knowledge and confidence that the equipment used meets known legislation. The vast majority of steam trap manufacturers do not conform to these International Standards. Spirax Sarco are always at the forefront of steam trapping developments and together with the British Standards Institute have been very active over the years, in their efforts to establish official standards for steam traps. In recent years certain British Standards have been modified to comply with both European (EN) standards and International (ISO) standards. A brief description of each is given below.
Glossary of technical terms for automatic steam traps ISO 6552 : 1980
7.3 1
This standard establishes precise definitions for all technical terms and expressions used to describe steam traps under operating conditions. Only by specifying these operating conditions can a customer be confident that the steam trap will safely operate within their system.
Permissible working pressure which is dependent on materials, design and working temperatures / pressures.
PN
Nominal pressure
PMA Maximum allowable pressure (bar)
That the shell of the trap can withstand at a given temperature.
Which is given by the manufacturer. Sometimes restricted by the pressure limitations of internal mechanisms.
PMO Maximum operating pressure (bar)
PO Operating pressure
Measured at the trap inlet (bar).
POB Operating backpressure
Measured at the outlet of the trap (bar).
PMOB Maximum operating backpressure (bar)
Maximum permissible pressure at the trap outlet allowing correct operation.
Operating differential pressure (bar)
Difference between operating pressure and operating backpressure (bar).
D P
11.3.2
Maximum difference between operating pressure and operating backpressure.
D PMX Maximum differential pressure (bar)
Minimum difference between operating pressure and operating backpressure.
D PMN Minimum differential pressure (bar)
PT
Test pressure (bar)
Pressure applied to the steam trap under test.
PTMX Maximum test pressure (bar)
Maximum cold hydraulic test pressure the trap can withstand, with internals fitted.
Maximum temperature to which the shell of the trap can be raised permanently, at a given pressure.
TMA Maximum allowable temperature ( o C)
TMO Maximum operating temperature ( o C)
Maximum temperature for which the operation of the trap is guaranteed.
TO
Operating temperature ( o C)
Temperature measured at the inlet of the trap being tested.
TI-F01-27 CMGT Issue 7
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Steam Trap International Standards
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