General information

Steam traps - International standards

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 2013

11.3.1

TI-F01-27

ST Issue 5

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 97 / 23 / EC.

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

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.

PN

Nominal pressure

PMA

Maximum allowable pressure (bar)

PMO

Maximum operating pressure (bar)

PO

Operating pressure

POB

Operating backpressure

PMOB Maximum operating backpressure (bar)

P

Operating differential pressure (bar)

PMX Maximum differential pressure (bar)

PMN Minimum differential pressure (bar)

PT

Test pressure (bar)

PTMX Maximum test pressure (bar)

TMA

Maximum allowable temperature (

o

C)

TMO

Maximum operating temperature (

o

C)

TO

Operating temperature (

o

C)

Marking of automatic steam traps

Permissible working pressure which is dependant on materials, design and working

temperatures / pressures.

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.

Measured at the trap inlet (bar).

Measured at the outlet of the trap (bar).

Maximum permissible pressure at the trap outlet allowing correct operation.

Difference between operating pressure and operating backpressure (bar).

Maximum difference between operating pressure and operating backpressure.

Minimum difference between operating pressure and operating backpressure.

Pressure applied to the steam trap under test.

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.

Maximum temperature for which the operation of the trap is guaranteed.

Temperature measured at the inlet of the trap being tested.

EN 26553 : 1991 ISO 6553 : 1980

Establishes certain minimum basic requirements for the marking and identification of steam traps. To conform to this standard all traps should

be marked with the following :-

Manufacturer’s name and / or trade mark

Maximum allowable pressure (PMA)

Maximum allowable temperature (TMA)

Indication of the flow direction

Optional markings to include:-

Nominal pressure (PN)

Maximum operating pressure (PMO) or maximum differential pressure (PMX)

Shell material designation

Nominal size (DN)

Maximum test pressure (PTMX)

If steam traps do not have this information clearly marked on them many insurance companies may not validate or insure the

steam system.