Water Supply Systems

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Water Systems for Small Communities

A Puzzle Guide for Local OfficialsBulletin 910

Water System Pressure Sources

eff Morrison, Assistant Director, Operator Training Committee of OhioKaren Mancl, Professor Food, Agricultural and Biological Engineering, The Ohio State University

Water system pressure ensures customers an adequate flow of water into their home or business. Pressure also providesdequate flow to fire fighting equipment. Even more importantly, water pressure protects the quality of water by

making sure that any leaks in the system result in clean water leaking out, not contaminated water leaking in.

Water pressure in a community water system is measured in pounds per square inch (psi). Household water pressurehould range from 50 to 60 pounds per square inch. A minimum of 20 pounds per square inch is required by law.

Water pressure will likely vary throughout the system. The highest points in the community and the most distantonnections will have the lowest pressure. The lowest points in the community and those closest to the pressure source

will have the highest water pressure. Water systems use booster pumps and pressure reducing valves to moderateressure within the system.

Pumps

umps at the water plant are the source of water pressure throughout the system. In some systems the well pumpsrovide the water pressure for the system. If pressure is reduced through the water treatment process, high-service

Page 1 of 3Water Systems for Small Communities: A Puzzle Guide for Local Officials, Bulletin 910

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umps deliver water to the system at adequate pressure.

Maintaining Water Pressure

Water systems have three options to maintain pressure throughout the system. A community may use a combination of ll three approaches to provide adequate water pressure to customers in different parts of their service area.

ank and Booster Pump

he tank and booster pump combination is probably the most reliable method of supplying pressure to a wateristribution system. When water demand causes the level in the tank to drop, the booster pump starts. The pumpupplies the demand for water with excess backing up into the tank. When the tank reaches the upper limit, the pumphuts off.

y having the tank, constant pressure is put on the system by the height of the water in the tank. The tank provides areater, more steady volume of water as well. During short power outages, the tank can provide pressure to the system.he Ohio Environmental Protection Agency requires that elevated storage be adequate to hold a one-day supply of

water to the areas it serves without pumping.

he tank and booster pump combination requires a lot of space and is the most expensive to engineer and construct.

he tank and booster pump system is suited for a large service area. Even if the initial service area is small, it is easy toxpand.

Hydropneumatic System

he hydropneumatic system consists of a pressure vessel and a pressure pump. The pressure vessel contains water withpressurized air space to provide the pressure for the system. With water demand, water flows from the vessel,

ncreasing the air space as well as decreasing air pressure. This lower pressure signals the pump to start. The pumpmeets the demand with the excess volume backing up in the pressure vessel. This decreases the air space and increaseshe pressure once again. When the upper level is reached, the pump shuts off. The newer pressure vessels have aeoprene bladder to separate the air space from the water.

hese systems are common in homes with an individual well system. They typically provide adequate pressure but lowolume. They are ideal for a rural water system that has a limited service area that is elevated from the main lineesulting in inadequate pressure. Hollows, cul-de-sacs, and small trailer parks utilize these to increase pressure. Some

water systems have small hydropneumatic stations added as the system expands. These stations are relativelynexpensive to engineer and construct and are often available as package units.

ome of the problems with hydropneumatic stations are that while they provide adequate pressure, they provide limitedolume. In some instances, with the nonbladder pressure vessels, air may be forced into the water lines if the demandor water exceeds pump capacity. Also, if the air space in the vessel is lost due to leakage (waterlogging), the pressureump will stop and start too frequently, resulting in erratic pressure and low water volume. Also, pressure will not last

ong during power outages.

Variable Demand Pressure Pump

Variable demand pressure pump systems consist of a continuous-run pump with control values to divert flow noteeded for demand around the pump and back into the pump intake. A similar system uses a variable speed motoreostatically controlled by pressure. These systems are utilized in much the same way as hydropneumatic systems.hey can handle larger sections and can provide more volume. They require careful engineering, are rather expensive

o purchase, but take up the least space.

ome of the problems encountered with these systems are their high operating cost due to the continuous-run feature,

igher maintenance frequency, and the total and immediate loss of pressure in a power outage.


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Comparing the Systems

ack | Forward | Table of Contents

Merits Limitations

Elevated tank with boosterpump

Most reliable (stores large watervolume)

Least expensive to operate

Can provide fire protection

Most expensive to construct

Requires two sites: one for pump/one large sitefor tank

Hydropneumatic systems Lower construction costs

Requires only one site

Less reliable (stores small water volume)

No fire protection

Variable demand pressurepump

Lowest construction cost

Requires only one small site

Least reliable (no water storage)

High operating costs


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