Unit 315 Session 6a Backflow protection in plumbing systems

​Mechanical backflow prevention devices

Open Ended

What do you think Mechanical backflow prevention devices are, can you name any?

​Mechanical backflow prevention devices

​An air gap is the most effective method of preventing

contamination of the water supply and most installers

will try to achieve this within their installations and

designs but there are many cases where air gaps are

not practical as a method of protection.
In these instances, installers may opt to install a mechanical

backflow prevention device.
These provide a physical barrier to backflow. However, it must be remembered that mechanical backflow prevention devices have

limitations and can be subject to failure.

​Type BA – verifiable backflow preventer with reduced pressure zone (a reduced pressure zone valve)

​Better known as an RPZ valve, this is a mechanical, verifiable, backflow prevention device, offering protection to water supplies up to and including fluid category 4. Verifiable simply means that the valve can be checked via test points to see if it is working

correctly (verified).

​Most RPZ valves consist of three separate elements:

● two check valves

● a differential relief valve

● three test points.

Match

Match the following descriptions with the backflow protection device

• These devices are used to prevent the backflow of water in plumbing systems. They are typically installed at cross-connections and are suitable for fluid category 2.

• Water flows through a chamber containing a flexible rubber diaphragm. If the supply pressure suddenly stops, the diaphragm is forced against the chamber wall to prevent backflow. These devices are designed for fluid category 5 applications.

• They consist of a spring-loaded one-way

  valve that will allow water to flow from upstream to

  downstream only. If back siphonage or back pressure

  occurs, the valve will shut to prevent a reverse water

  flow. used to protect

  against fluid category 2

• Consisting of two single check valves in series,

  which will permit water to flow from upstream to

  downstream but not in the reverse direction. They are

  used primarily to protect against fluid category 3

• This mechanical backflow

  prevention device screws on to the outlet thread of a

  hose union bib tap.

Type AB – air gap

Type DB interrupter

EA & EB single check valves

Type EC & Type ED Double check valves

Type HA – hose union backflow

preventer

• Type AB – air gap

• Type DB interrupter

• EA & EB single check valves

• Type EC & Type ED Double check valves

• Type HA – hose union backflow

  preventer

​Research project

​You are to use appropriate sources to produce a word document giving a brief description accompanied with an image of the following 7 types of mechanical backflow protection.