Riser Diagrams for Water Supply
Riser diagrams for water supply show both the hot and cold water lines. Their layout and specification is simpler than waste pipes and designers have more freedom because the pipes are under pressure. Generally, water supply pipes can go anywhere because they are not linked to drains and vents.
Of course, the design of the building water distribution system will determine the layout of the plumbing riser diagram, whether or not waste water, and so in, is included in the diagram.
Both the flow rate and the flow pressure are important criteria for water distribution systems and pipe sizes need to be selected in keeping with conditions of peak demand.
The minimum size of fixture supply pipe varies according to the fixture it is supplying water to. So, for instance, 3/8 inch pipe is adequate for lavatories, some water closets, lavatories, bidets, and drinking fountains, but ½ inch pipe is more usual and required for bathtubs, domestic dishwashers, kitchen sinks, single-head showers, and wall hydrants. Flush-valve water closets require a bigger 1-inch pipe. Each fixture supply pipe requires a stop valve of the required type. The supply pipe must also extend to the floor or to a wall adjacent to the fixture that is supplied with hot or cold water. Sometimes water-pressure reducing valves or regulators are required.
Another important aspect of water supply is that potable (drinkable) water must not be contaminated in the system. This means that it is essential to ensure that non-potable liquids, solids, or gases cannot escape into the water supply piping. Various backflow preventers are mandatory. They include:
- Air gaps that provide an unobstructed vertical distance between the lowest opening of a pipe or faucet that supplies water to a tank, or a plumbing fixture or device.
- Air gap fittings that are used with plumbing appliances, fixtures, and appurtenances.
- Antisiphon-type fill valves used for gravity water closet flush tanks.
- Pressure vacuum breaker assemblies.
- Backflow preventers that work on the principle of reduced pressure.
Additionally, supply lines and fittings for plumbing fixtures must be installed so that there is no chance of backflow.
Riser Diagrams for Stacks
We have already said that stacks include sanitary, storm, and vent piping.
Sanitary piping conveys sewage. Storm piping conveys storm water, groundwater and potable clear water waste from fixtures and appliances. It doesn’t contain any sewage or fecal matter. However, we sometimes use waste pipes that only convey waste water.
Vent pipes are part of a vent system that incorporates pipes that are designed and installed to provide airflow to or from drainage systems. They are often designed to protect trap seals, fitted to prevent the emission of sewer gases, from backpressure and siphonage.
Other terminology relating to stacks and vent piping includes reference to:
- Stack vents that extend above the highest horizontal drain connected to the stack.
- Stack venting that is a way of venting fixture through soil or waste stacks.
- Vent stacks are the main vertical vent pipes in the drainage system.
- Back vents are vent stacks that are connected to stack vents or the branch discharge pipes we sometimes connect to unvented discharge pipes.
- Trap vents that connect to traps that open to the air or to other vent pipes.
- Discharge stacks that lead to two or more sanitary fixtures and are connected directly to a drain.
Like water supply pipes, the pipes used for sanitary or soil, waste, and vent pipe are governed by the NYC Plumbing Code and the standards specified in the Code. Generally, the pipes are a lot bigger than the pipes used for water supply. For instance, WC pipes are usually 3.5 to 4 inches.
We have already discussed the need to separate water supply pipes from the drainage system. Piping used for supply and drainage run parallel but they must never touch because of the dangers and risks of contamination.
While air gaps or valves may be used, air gaps are more common. In a drainage system, an air gap is defined as the unobstructed vertical distance “through the free atmosphere” between a waste pipe outlet and the flood level rim of the receptacle into which the waste pipe discharges.
All these pipes must be shown on the plumbing riser diagram.
Risers for Sprinklers
Fire sprinklers are now mandatory for all business buildings that are 100 feet or taller. This includes high-rise office buildings.
While the NFPA standards cover the design and installation of sprinkler systems, if these are included in any plumbing system, they need to be included in a plumbing riser diagram.
Also, if non-potable water is installed in a building for the use of fire sprinklers, piping must be identified with metal tags or with a color. For instance, purple is used to identify rain, recycled, and gray water distribution systems. In New York, outlets that discharge non-potable water must also be identified, specifically with the words: “Caution. Nonpotable Water. Do Not Drink.”
There is, of course, a lot more to plumbing engineering than we have mentioned here. Nearby Engineers New York Engineers has a trained team of professionals to work on the full range of projects. Call for a consultation to see how we can help you.