Module 2 Cold Water Systems Flashcards
What are trunk mains ?
They may be as much as 610mm (2ft) in diameter they carry the water in bulk and often over long distances to the built up areas,
What are street mains??
They are pipes off trunk mains, they can be mostly 100mm(4in) which run beneath the street and side streets
How is the plumber involved in connecting to a mains?
It’s usually done by trained main layers but a plumber must arrange for a suitable connection to be made to the main before he can connect a cold water supply to any building
What is the name of the tool used for tapping into a mains?
A ferrule
What will the plumber be responsible for at the ferrule?
For the services connected to the tapping ferrule, can be called to install smaller diameter mains for fire fighting services and extensions to mains within the bounds of a large new building
What way will water mains be laid out in a town in?
Laid out in the form of a grid, the grid provides a ring circuit and each section can be isolated bin the event of a burst mains or backwashed for cleaning as desired without the need to isolate the full town supply
How far below ground should water mains be?
900mm beneath roads and 750mm elsewhere in order to prevent damage owing to settlement or frost
What can water mains be made from??
Pvc , asbestos cement or cast iron
Asbestos cement mains what are they?
These have been used with safety for conveying water which could corrode iron pipes, in can come in various thickness and can withstand the same internal pressures as cast iron
Pvc explains out it?
It is widely used and has sufficient thickness and strength to enable connection to be made
Cast iron mains explain it?
Cast iron mains has proved to be very satisfactory the only problem is their susceptibility to deterioration in certain corrosive soils
What is a mains tapping machine?
A special machine designed to cut into large diameter cast iron distribution mains pipes while the water is still in the pipe and under pressure
What is the name of the pipework from the street water mains to the external local stop valve called??
It’s know as the communication pipe and is connected to the ferrule
What is the name give to the pipe connected to the ferrule that has a bend?
It’s called a goose neck bend and is purposely put into the communications pipe to allow for ground movement
What is the name of the pipe from the stop valve into the house called?
This is know as the service pipe and is usually 750mm underground
What should be done to underground pipe work?
It should be sleeved and both ends should be sealed with mastic to prevent the entry of vermin etc into the house
What are the names of all the calves on the mains going into a house?
Stop valve, double check valve, drain valve, rising mains
What is the stop valve on the pipe mains?
It’s the first fixing on the service pipe which allows the household to control the flow of water into the premises
What is the double check valve on the pipe mains?
Fitted to prevent any occurrence of back siphonage
What is the drain valve on the mains pipe?
It is fitted to allow the pipe work to be drained
What is the name of the pipe from the drain valve on?
Know as the rising mains
What is a direct system?
All pipes to the cold draw off points bare taken directly from the rising mains
What size cistern should be used in a direct system?
A min of 135lt or same size as the hot water storage cylinder
What is an indirect system?
This is when the rising mains pipe rises through the building to the cold water storage cistern and only on draw off point for drinking purposes is permitted
What is the capacity of the cistern in an indirect system?
The cistern should be a min of 227lt
What are water mains?
Water mains are pipes of large diameter used to carry POTABLE water( drinking water)
What is backflow prevention?
It’s the term used to prevent the reverse flow of water from a potentially polluted or contaminated source into drinking water
What must appliances that are connected to mains have??
They all must have some means of backflow prevention
What is an air gap??
There are many types of air gaps but simply put an air gap is physical separation measured vertically through the air between a water supply outlet and the flood level rim
All pillar taps provide air gaps but care must be taken with placement of BIB TAPS
Learn
What is the best prevention from back sipononage?
An air gap
The provision of a backflow prevention device such as a non return valve or anti vacuum valves
Non return valves do not give 100% protection against back siphonage
What should be fitted to an outside BIB TAPE?
Special non return valves as they can have hoses connected which trail into ponds
Name the two most common check valves?
The spring type and the flap type
Where are spring non return valves used?
Most commonly used on mains water system
Where would the flap non return valve be used?
They offer little resistance and is used commonly on pumped heating systems
Advantages of a direct system?
Smaller cistern, cheaper to install, drinking water
Disadvantages of a direct system?
Danger of back siphonage, danger of water hammer, pressure losses, no cold storage
Advantages of the in direct system?
Less risk of back siphonage, less risk of water hammer, adequate store of cold water
Disadvantages of the in direct system?
More expensive, larger cistern, less drinking water
