Water Distribution: pumping systems, pipes, fittings & valves

  

PAUL HAY Capital Projects

www.phcjam.com

Subject:         Water Distribution

Author:          Paul Hay

e-mail:            paul.hay@phcjam.com

profile:           www.linkedin.com/in/phcjam

1.0       INTRODUCTION   

1.1       An adequate supply of potable water shall be provided to each plumbing fixture;

1.2       Water shall be distributed in a manner that ensures it is kept clean and sanitary;

1.3       Good design requires sufficient fittings and valves for ease of maintenance; and

1.4       There should be minimum interference with the architectural form.

2.0 DISTRIBUTION SYSTEMS

2.1       Up-feed distribution involves the distribution of water under the pressure available at the water main or from pressure tanks fed by pumped wells:

            2.1.1   Up-feed systems are primarily used in low-rise buildings;

            2.1.2   Water pressure available at the main must be greater than 103 kPa (15 psi);

            2.1.3   Otherwise, pressure available at main shall exceed losses due to (a) flow through meter, (b) fiction in piping, and (c) height of water column in order to provide proper flow pressure to the highest fixture.

Figure 1: Upfeed Distribution System [source:- Journal of Light Construction Field Guide (vol. 2)]

2.2       Pumped Up-feed Distribution utilizes pumps to supply the additional pressure required:

            2.2.1   Water must first be collected in low-level storage tanks (because direct connection of pumps to the water main is illegal in Jamaica);

            2.2.2   Pumped up-feed systems are primarily used in medium-rise buildings;

            2.2.3   Back-up generators must be provided to allow distribution of water during a power outage.

2.3       Down-feed distribution involves the pumping of water to upper level storage tanks which gravity feed to plumbing fixtures:

            2.3.1   Static Pressure is the pressure exerted by a column of water by virtue of its depth below its stationary head;

            2.3.2   Tanks shall be elevated in order to provide the static pressure needed on the floor immediately below;

            2.3.3   With insufficient head, tanks can be pneumatically charged with an air compressor to attain the required pressure:

                        2.3.3.1            Air-charged pneumatic pumping systems result in greater levels of dissolved air which may result in an undesirable “fizz” on discharge;

                        2.3.3.2            Dissolved oxygen increases corrosiveness of the water supply.

            2.3.4   Water distribution for high-rise buildings should be divided into zones up to 45 m (150 ft.) high:

              2.3.4.1          Static pressure beyond this height can damage plumbing fixtures;

              2.3.4.2            Each zone must be served by independent distribution systems and plumbing.

3.0       PIPES & FITTINGS

3.1    Water supply pipes and fittings can be brass, cast iron, malleable iron, galvanized wrought-iron, galvanized steel, or several types of plastic:

            3.1.1   Copper does not corrode and is durable:

                      3.1.1.1            Copper is subject to electrolytic attack if connected to a dissimilar metal without dielectric separation;

            3.1.1.2            Fittings can be (a) by flared compression joint,  (b) solder-type or brazing fittings;

                        3.1.1.3            Copper’s smooth interior permits the use of smaller sized pipes; and

                        3.1.1.4            Copper pipe should not be used for hot water systems where temperature exceeds 60EC (140E F).

            3.1.2   Galvanized Steel has a long service life:

                        3.1.2.1            Galvanized pipes are dimensionally stable and strong;

                        3.1.2.2            Pipes used in water distribution are joined with screwed fittings;

                        3.1.2.3            Pipes may be used for both cold and hot water distribution, and

                        3.1.2.4            Water Treatment may be required against corrosiveness of water.

         3.1.3   Rigid Plastic Pipe is light-weight offering exceptional resistance to (a) chemicals, (b) impact, and (c) pressure:

                        3.1.3.1            Rates of expansion exceed those of copper and steel;

                        3.1.3.2            Special adapters are available for joints with metal pipes;

                        3.1.3.3            Fittings are typically solvent-welded to the pipes;

                        3.1.3.4            Polyvinyl Chloride (P.V.C.) is one of the common types;

                        3.1.3.5            Polyvinyl Dichloride (P.V.D.C.) Should be used to carry hot water no hotter than 82E C (180E F).

3.2       Except for valves and similar devices, fittings used must be the same material as the pipe;

3.3       Pumps shall be connected with unions;

3.4       Cross connection is an arrangement of piping or connections that allows contamination:

            3.4.1   Syphoning of contaminants occurs when there is a difference in pressure, or a vacuum, in the water distribution system;

            3.4.2   Air gap or Air break is the vertical separation between a pipe or faucet and the flood-level rim of the receptacle;

            3.4.3   Back flow or Check valves allow water to flow in only one direction.

Figure 2: Drainpipe Fittings [source:- Journal of Light Construction Field Guide (vol. 2)]

4.0       VALVES & CONTROLS

4.1       Pressure Regulators should be used in cases when (a) water pressure in mains is excessive, and (b) with problems of variable pressure at different floor levels;

4.2       Valves shall be used (a) on each riser, (b) on each branch to bathrooms, kitchens, etc. and (c)  run-outs to individual fixtures.

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FURTHER READING

Mechanical and Electrical Equipment for Buildings, Benjamin Stein & John S. Reynolds, John Wiley & Sons Inc., U.S.A.

Construction Materials & Processes, Don G. Watson, McGraw-Hill Book Co., USA.