Steam Main Jargon Buster


The Safety Assessment Federation. Represents the UK independent engineering inspection and certification industry, which plays a key role in maintaining high standards of safety within the workplace.

Safety valve or safety relief valve

A type of valve that automatically discharges steam, gas, or vapours so as to prevent a predetermined safe pressure being exceeded. Safety valves should be used on any closed vessel or system in which the pressure can be other than atmospheric and where in any circumstances the design pressure of the system can be exceeded.

Sample cooler

A devise which is used to cool blowdown water to a datum temperature of 25 °C for sampling, or can be used to condense a sample of steam for the same purpose.


This is the process where pathogenic and other kinds of microorganisms are destroyed.

Saturated steam

Saturated steam; is the type of steam most commonly used. Steam in this state has a temperature that corresponds to the boiling temperature of water at the existing pressure. The properties of saturated steam make it an excellent medium for heat transfer. Therefore it is widely used in the 130 - 200 °C temperature range.

Saturated steam system

A system incorporating; generation, distribution, and utilisation, which is designed to operate with steam in a saturated state.

Saturation point

The point at which condensation is formed.


Stands for supervisory control and data acquisition. An industrial control system (ICS) which is a computer system that monitors and controls industrial infrastructure, or facility based processes.


A layer which can form on metal and other surfaces. It is caused by impurities precipitating or settling out of water onto surfaces. It can reduce thermal efficiency as well as causing operational issues.


A steam separator is a device which removes moisture entrained in the steam to provide dryer steam. It does this by turning and changing direction of the steam causing the moisture to drop out where it can be removed using a steam trap.

Set point or actuation point

The exact pressure or flow rate which will cause an electrical switch to actuate.

Solid state

Any element that controls current without moving parts, vacuum gaps or heated filaments.

Spirax Sarco

A company which manufactures and provides a wide range of goods and services to the steam industry (from steam traps to heat exchangers). It is part of Spirax Sarco Engineering plc which is a multi-national industrial engineering group quoted on the London Stock Exchange since 1959.

Stainless steel

A common name given to a type of steel. Stainless steels containing about 18% chromium and 8% nickel, 18-8 austenitic stainless steels are regularly used materials for services at elevated and sub-zero temperatures and for highly corrosive conditions. The addition of molybdenum to the basic type of 18-8 stainless steel and a slight increase in nickel material increases the corrosion resistant properties and 18-10-3-Mo steels are used extensively in the chemical industry for handling acetic acid, nitric acid, alkalis, bleaching solutions, food products, fruit juices, sulphurous acids, tanning liquors, and other industrial chemicals. For use at elevated temperatures a further modification is made by the addition of niobium and this steel, known as 18-10-Nb°is suitable for temperatures up to 800 °C.


This is the condition where condensate cannot be removed from a heat exchanger or similar equipment. It happens where the operating differential pressure between the inlet and outlet of the steam trap is so small that 'condensate' is not discharged from the steam trap, and instead leads to the waterlogging of the equipment.

Steady state

A stable condition that does not change over time or in which a change in one direction is continually balanced by changes in another.


Formed from water. Steam is formed when water is heated above a certain point it is converted into a vapour. This vapour is a white mist with minute droplets of water in the air. When water is boiling and continues to be heated in a boiler it will evaporate to form this vapour which is called steam.

Steam injection

A process where steam is injected into a liquid to heat it. The steam condenses in the liquid and gives up its energy, raising the liquids temperature.

Steam tables

These are tables that allow steam designers and users to look up data on the properties of steam. This so they can make calculations to ensure the best use of steam. It can also be used identify and diagnose problems. The tables themselves are a collection of data on temperature, pressure, volume, and the energy contained in water and steam. This data is traditionally expressed in the form of a table with columns for reading the data.

Steam trap

A device which discharges condensate and non-condensable gases when they form and closes and traps when there is none. On a steam system it is important that steam does not leak through a steam trap and that the trap closes properly where there is only steam present. It is however also important that when condensate or gases are present that they are removed from the system. If condensate is not removed it can be a safety issue as well as causing possible process issues. Steam traps come in different types and sizes according to the application.

Steam trap management

Steam traps are an important part of a steam system. Therefore it is important that they are inspected and checked on a regular basis. This should be in the form of a steam trap management regime. This would normally involve regular steam trap survey checking to ensure that the steam trap is; not failing open and passing live steam (and wasting energy), or failed closed and not removing condensate as it should (which could cause operational issues).

Steam turbine

A steam turbine uses the flow of steam from a higher to lower pressure to turn a turbine. The turbine could then be used to turn a range of equipment including a generator for electricity.


A term that is used to express the rate of steam produced in a steam boiler. Usually expressed in kg/hr or Lbs/hr.


Generally used to describe the process of using steam under pressure in an autoclave to make sure that items are made sterile to a certain standard.


A device which is fitted in the pipework to remove solids from steam and other fluids. The strainer will use a strainer element which is a mesh or perforated tube to do this. Strainers can come in many different forms but the most common is probably the Y shaped type. It is important that strainers are used upstream of equipment to make sure that the equipment is protected from possible damage.

Stuffing box packing

Stuffing box packing or compression packing is a steam seal packing used for most liquid and gas services on valves. A spigoted gland, bolted or threaded applies a compressive force to the packing and the resulting radial pressure of the packing on the steam provides the seal. Springs can also be used to create the compressive force to the packing and are useful where the gland assembly is inaccessible. They do not provide the fine degree of adjustment needed for many critical duties.

Sub-cooled condensate

Condensate that has cooled to a temperature below its saturation temperature.

Superheated steam

Superheated steam is formed by the further heating of saturated steam. Therefore superheated steam has a higher temperature than saturated steam at the same pressure. Superheated steam is not as commonly used as saturated steam. It is a very dry steam, these properties mean it is used mainly for physical drive or propulsion applications (e.g. steam turbines), and is not often used for heating purposes.

Surplussing valve

A type of valve that automatically controls the release of fluid to another system (or atmosphere), and therefore maintains a set pressure within the system it is controlling.

Syphon tube

A the pipe that removes condensate from inside a rotating cylinder, where it can be routed to a steam trap. It is typically used in the paper industry or laundry calenders.

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