Steam Main Jargon Buster

Wafer check valve

A type of check, or non-return valve which only allows flow in one direction through it (please see check valve description). The Wafer type family of check valves is usually considered to consist of the following valve designs; disc, split disc, and reduced bore swing type.

Wall thickness

A term used to describe the thickness of material that a pipe is made from. As the wall thickness is increased (for different types of pipe design and standards) for a given size of pipe the bore will be reduced, while the outside diameter will stay the same.

Water hammer

When a column of flowing liquid is suddenly stopped, a pounding of the line, commonly known as water hammer is usually produced. For sudden flow stoppage, the pressure rise due to the deceleration of a truly incompressible fluid in a non-expanding pipe would be infinite, the fluid in the line would behave as a 'plug' and the pressure rise would be that corresponding to the inertia effects of this plug. Experience has shown that there is a finite maximum pressure rise, because part of the kinetic energy of the moving fluid in the pipe is expended in stretching the pipe walls and compressing the fluid. Water hammer can be potentially very dangerous. In a steam system its can be the result of; not enough steam traps, poor system design, or poor maintenance resulting in steam traps failing shut and not removing condensate.

Water softener

A piece of equipment, or system which is used to remove calcium and magnesium hardness minerals from a water supply.

Water treatment

Describes the process where 'raw water' is treated so that it is of the correct quality, so that the boiler, steam, and condensate systems functions correctly and do not break down or suffer harm.

Water tube boiler

A type of steam boiler where the water is contained and circulated in tubes and the heat source is surrounding them. They are typically used more for superheated steam production.


In a steam system, this is the flooding of the steam space with condensate. It is undesirable as it usually results in loss of heat output, corrosion, and thermal stress.

Wet back boiler

A type of steam boiler which has the back end combustion chamber surrounded by a water jacket as part of its design.

Wet steam

A term used to describe steam at its saturation temperature that contains entrained water.


A term used to describe the erosion of valve seats and other types of orifice. It is caused by droplets of water suspended in the steam.

Withdrawal distance

The distance that equipment has to be kept from its surroundings and other equipment to allow the removal of parts for maintenance purposes.

© Copyright Steam Main Limited 2017-2018 All Rights Reserved

Site by Banilla