Back siphonage
|
| This backflow prevention device includes a valve assembly with isolation valves and strainer. |
Collins Complete Do-It-Yourself Manual was published in 1986. It was created for William Collins Sons & Co. Ltd. by Jackson Day and conceived by Jackson Day Jennings Ltd.
It defines back siphonage as: ‘The siphoning of part of a plumbing system caused by the failure of mains water pressure’.
The negative pressure (or vacuum) that results in back siphonage can happen under conditions such as a water mains break or an increased use of water for fire fighting or construction purposes. When the vacuum occurs and the supply pressure decreases, back siphonage causes the water flow (or other liquid substances) to reverse.
Back siphonage may result in contaminated water being pulled into the clean water supply. This action is referred to as backflow. Backflow can also take place due to back pressure, which can occur when there is higher pressure in the system than in its supply. This can happen in certain types of heating systems where the pressure is increased for some reason (such as thermal expansion in unvented systems).
[edit] Preventing back siphonage
Air gaps can be used to help prevent both back siphonage and backflow. An air gap is a cleared vertical space that is placed in a way that allows it to control the water supply. These gaps can be used to regulate the pressure.
An atmospheric vacuum breaker (or AVB) can be used to prevent back siphonage. It is a type of backflow prevention device that can be used in situations where it is not possible to create an air gap.
Water-using appliances must provide an acceptable degree of protection against backflow or back siphonage. These parameters are determined in BS 6280:1982 Method of vacuum (backsiphonage) test for water-using appliances. Recommendations are also proscribed under the Water Supply (Water Fittings) Regulations 1999.
[edit] Related articles on Designing Buildings
- Backflow.
- Mains water.
- Plumbing.
- Potable water.
- Siphon.
- Vacuum breaker.
- Warning pipe.
- Water consumption.
- Water Services Regulation Authority.
- Water Supply (Water Fittings) Regulations 1999.
[edit] External resources
Featured articles and news
The Home Energy Model and its wrappers
From SAP to HEM, EPC for MEES and FHS assessment wrappers.
Future Homes Standard Essentials launched
Future Homes Hub launches new campaign to help the homebuilding sector prepare for the implementation of new building standards.
Building Safety recap February, 2026
Our regular run-down of key building safety related events of the month.
Planning reform: draft NPPF and industry responses.
Last chance to comment on proposed changes to the NPPF.
A Regency palace of colour and sensation. Book review.
Delayed, derailed and devalued
How the UK’s planning crisis is undermining British manufacturing.
How much does it cost to build a house?
A brief run down of key considerations from a London based practice.
The need for a National construction careers campaign
Highlighted by CIOB to cut unemployment, reduce skills gap and deliver on housing and infrastructure ambitions.
AI-Driven automation; reducing time, enhancing compliance
Sustainability; not just compliance but rethinking design, material selection, and the supply chains to support them.
Climate Resilience and Adaptation In the Built Environment
New CIOB Technical Information Sheet by Colin Booth, Professor of Smart and Sustainable Infrastructure.
Turning Enquiries into Profitable Construction Projects
Founder of Develop Coaching and author of Building Your Future; Greg Wilkes shares his insights.
IHBC Signpost: Poetry from concrete
Scotland’s fascinating historic concrete and brutalist architecture with the Engine Shed.
Demonstrating that apprenticeships work for business, people and Scotland’s economy.
Scottish parents prioritise construction and apprenticeships
CIOB data released for Scottish Apprenticeship Week shows construction as top potential career path.
From a Green to a White Paper and the proposal of a General Safety Requirement for construction products.
Creativity, conservation and craft at Barley Studio. Book review.
The challenge as PFI agreements come to an end
How construction deals with inherited assets built under long-term contracts.
Skills plan for engineering and building services
Comprehensive industry report highlights persistent skills challenges across the sector.
Choosing the right design team for a D&B Contract
An architect explains the nature and needs of working within this common procurement route.
Statement from the Interim Chief Construction Advisor
Thouria Istephan; Architect and inquiry panel member outlines ongoing work, priorities and next steps.