Water hammer
In plumbing
A short-lived pressure wave associated with an abrupt change in liquid velocity. It can produce a bang when a valve closes rapidly. Diagnosis considers operating pressure, flow behaviour and pipe restraint rather than assuming every plumbing noise needs the same accessory.
Using Water hammer in a plumbing system
Updated
A distinction worth remembering
A closure-related bang, a warm-up tick and gurgling can point towards different mechanisms. Compare timing with valve operation and water movement, and use the evidence to choose the next safe observation.
Questions to take further
- Does a noise by itself identify the replacement part?
- No. The source, pressure conditions, pipe supports and operating pattern need investigation. Several causes can be present in one installation.
Sources
- Skills England: plumbing and domestic heating technician — The systems, materials, planning and customer responsibilities in the England occupational standard.
Where Water hammer fits in the learning path
The Level 3: diagnosis, design, commissioning and handover section covers these topics:
- Water hammer and plumbing diagnosis
- Working out room heat loss
- Planning, commissioning and handover
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- Water hammer and plumbing diagnosisLevel 3: diagnosis, design, commissioning and handover
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How much water comes out of an outlet in a given time, usually measured in litres a minute by timing how long a container of known size takes to fill. It is different from pressure: a supply can have good pressure and poor flow if a pipe is narrow, partly blocked or shared with other outlets.
Flow rate
Read the Flow rate entryCompare related terms
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Flow rate
How much water comes out of an outlet in a given time, usually measured in litres a minute by timing how long a container of known size takes to fill. It is different from pressure: a supply can have good pressure and poor flow if a pipe is narrow, partly blocked or shared with other outlets.
Read the Flow rate entryPipe velocity
The average speed at which water travels through the pipe bore, commonly expressed in metres per second. For an unchanged volume flow, a larger internal area means a lower speed. A design also needs pressure-loss and operating-condition checks.
Read the Pipe velocity entryBefore you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.
A definition is a start. Using it in a real question is where it sticks.