The Dry Hydrant Concept
Dry Hydrant Advantages
Having water available in area streams, ponds and cisterns helps a fire department only if the water is readily accessible. The needed water may be located so far away from where it is needed that a fire department's ability to control the fire is impaired. Mobile water supply vehicles can move water from distant sources, but the critical factor is whether or not the fire department can maintain an uninterrupted supply of a predictable rate of water at the fire scene.
Installation of dry hydrants into nearby and developed water supplies eliminates the inefficiency and complexity of long-distance water shuttle operations. This arrangement also allows access to water sources from a roadway instead of having to work on soft ground immediately adjacent to the pond or stream.
In any area without water mains and domestic fire hydrants, the dry hydrant concept can provide a simple, cost-effective solution to the need for rapid access to water sources. A dry hydrant consists of an arrangement of piping with one end in the water and the other end extending to dry land and available for connection to a pumper. Dry hydrants have the following features:
- Use a non-pressurized pipe system.
- Use relatively inexpensive piping materials and other
- Are permanently installed in existing lakes, ponds,
streams and cisterns.
- Provide a means of access whenever needed, regardless
- Allow years of simple operation with a minimum of maintenance.
The time savings are many. Multiple lengths of hard suction hose extending to the water are not needed; usually one section to the dry hydrant is enough. The strainer is also permanently attached, saving more time. Fewer people are needed to make a hookup compared to make a conventional direct drafting hookup.
When a strategically placed dry hydrant with all-weather road access allows more water to be distributed in less time, and the water can be applied effectively on the fire, fire fighter effectiveness and safety is improved.
Savings can be financial as well. Fire departments save money by reducing fuel and equipment costs through shorter transportation distances and lower operational demands. Communities can preserve more of their treated water supplies, since dry hydrants use untreated water.
Planning for dry hydrants involves several considerations and should involve all affected agencies and individuals so a coordinated effort can take place. Some factors to consider are:
- Current and future population and building trends.
- Property values.
- Potential for loss.
- Fire history of the area.
- Current water supply systems.
- Other potential water sources.
- Cost of project.
- Equipment and personnel of the local fire department.
- Training needs of the fire department.
- Other specific factors of local concern.
Dry Hydrant Location
The location of individual dry hydrants is influenced by several factors. After conducting a water source survey of the area, use a county road map to mark potentially good sites. Mark them in priority order, since most fire departments will not have sufficient funding for all the dry hydrants that may be preferred. Consider these factors:
The authority should
contact the legal property owner to secure written permission (in conjunction
with the town or county attorney) to use the water source. If a possible dry
hydrant site is along a road right-of-way, you will need town, county or state
approval. In some cases US Army Corps of Engineers approval may also be
needed. Obtaining written permission is an important requirement that may take
- Maximum distance of travel between dry
hydrants. This can vary for several reasons, but a target distance could be
one dry hydrant every 3 square miles. This would produce a travel time of
about 6 minutes between the water and the fire, assuming an average safe
constant speed for a loaded truck of 35 mph.
should be made about the useful depth of a lake or pond, measured from the
minimum foreseeable low-water surface level to the top of the suction strainer
(not the bottom of the lake). The low-water mark considers drought, freezing
and other effects, such as where the water level is lowered to generate power.
The absolute lowest level must be not less than 2 feet, to prevent a vortex or
whirlpool which could allow air to enter the pump and cause loss of pump
prime. You may need a minimum of 4 to 5 feet of water over the suction screen
and pipe during low water to prevent a freeze-up of the screen.
- Depth of water at the source.
long-term useful hydrant operation, the best composition for the bottom of a
lake, stream or pond is sand, gravel or rock or a combination of these.
Decaying vegetative matter could clog the suction screen.
A backhoe will need to get
close enough to the water's edge to reach out and dig at least 5 feet below
the surface of the water to start the trench.
- Composition of the bottom material.
that is conveniently accessible to fire apparatus may also be exposed to
accidents from other passing vehicles. An impact barrier constructed of
partially buried posts may be needed to prevent a vehicle from destroying a
dry hydrant in a heavily traveled area. Special markings may be necessary to
avoid damage from snow plows.
The expense of a dry hydrant
installation depends on local practices and the length of pipe needed. The
Colorado State Forest Service has estimated the cost there to be between $500
and $1200, including the cost for contractor labor and machines.
- Protection of the connection.
in the digging
area. You must carefully check for the presence of buried lines and pipes and
notify utility companies before you start digging.
- Beware of other utilities
Design Features Checklist
Design factors are affected by:
- Desired flow from the hydrant in gallons per minute
- Suitability of pipe materials
- Size and type of fire apparatus pumper that is available
The following design features are suggested for dry hydrants using PVC pipes:
- Use minimum 6-inch-diameter pipes, schedule 40 pipe.
- Prime and paint all exposed pipe.
- Use a minimum of elbows.
- properly joint and cement all connections.
- Purchase or construct a suction screen with adequate hole openings. The total area of strainer holes must exceed 4 times the area of the diameter of the pipe.
- Installation depth must be below the frost-free depth
for the area. (Consult local university extension service or Larimer County
Building Department for frost depth.
- Install dry hydrant as close as practical to the water
- A flow of 600 to 1000 gpm from the hydrant is
- Avoid designs with lifts in excess of 12 feet. (Above
this height vapor pressure will begin to exceed atmospheric pressure and
cavitation will occur, making pumping virtually impossible.)
- Place the pump at a higher elevation than the hydrant
connection. (This will eliminate air bubbles which will limit flow, and also
prevent the operator from getting wet.)
- When rock is encountered, installation must be adjusted to fit the rock profile. (Additional bends may be necessary.)
- Each elbow in a dry hydrant installation increases
friction loss. Try using 45° elbows and a minimum number of 90-degree elbows.
- An access road with a minimum width of 12 feet and a
maximum grade of 8 percent.
- Does the site have proper drainage?
- Avoid vertical lifts of more than 12 feet with other
than Class A pumps.
- PVC piping greater than two full sections will require additional personnel for installation.
Construction of Dry Hydrants
Installation starts with arranging for a large backhoe and at least three people to handle and place the pipe in the trench. An ideal time to start installation is in the late summer when the water is warm and usually at its lowest level. Haul clean fill material to the site. Choose material that will not wash out easily. Follow these installation steps:
- Dig the trench. Mark the backhoe arm with a
ribbon to indicate the desired vertical depth. (This is helpful only when the
ground is level.) Start excavating the ditch in the water and complete the
entire horizontal section of the trench. Keep the bottom of the trench level
all the way to the hydrant. (It is less complicated to maintain a level trench
rather than a sloped one which requires figuring correct angles of joints.)
It is better to use two 45-degree
elbows for the riser joint instead of a single 90-degree elbow.
If your hydrant connection is later broken off accidentally, the wider sweep of
the 45-degree elbows would allow you to insert a 2 1/2-inch suction hose
into the pipe. (Some may prefer to apply primer at this point, before glueing the joints.)
- Cut the pipe to the desired lengths
and assemble. Check dry fit. As a rule of
thumb, 6-inch-diameter pipe will not flow 1,000 gpm at horizontal lengths greater than 100 feet.
- Join the pipe sections with glue. Make sure
you understand the technique, because timing is important. Use PVC cement;
never use all-purpose cement to join PVC pipe and fittings. Joints must be
held tightly together until both surfaces are firmly cemented. Do not disturb
the joint until initial set occurs, which varies according to the temperature.
Above 60 degrees, the recommended time is at least 30 minutes. Decrease the
chance for an air leak by taping the joints with a rubberized, adhesive-backed
wide tape. Attach the strainer with a collar or sleeve so that it can be
removed if necessary.
- Pressure test the joint only after adequate
curing according to the instructions for the particular cement. Do not take
- Carry the prepared piping to the trench.
- Force the strainer under water until it
fills the pipe. If more than 8 feet of pipe is out in the pond, a support
bracket behind the strainer is a good idea. Support can be as simple as
stacked concrete blocks. The strainer must be above the bottom of the pond so
that the strainer holes will not be clogged with mud or other debris. Proper
placement is necessary for successful operation of the dry hydrant.
with the riser, which should be covered during this operation to prevent rock
and fill from falling into the pipe. Tamp the dirt for rigid support. Mound
the fill material higher for more freeze protection. If extra insulation is
needed, install a styrofoam barrier around the pipe 2 to 3 feet under the
- Backfill around the pipe assembly
the distance from the bottom of the intake on the pump (positioned as it would
be for pumping) to the ground. Cut off the riser so that when you attach the
hydrant connection to the riser, the top of the opening of the hydrant
connection is lower than the bottom of the pump intake. That is, the pump
intake must be above the hydrant connection.
- Cut off the top of the riser
- Plant grass seed or other vegetation over the disturbed areas to retard erosion.
Mulching helps the seed or seedlings to get established.
(especially if using 45-degree elbows) remember that connecting a suction hose
and drafting through the dry hydrant connection places a lot of stress on the
to identify the dry hydrant and
warn people against parking or obstructing access. Paint the cap a reflective
color for improved visibility during emergencies. If the exposed PVC is not
sunscreen protected, the pipe must be painted to prevent chemical
decomposition from ultraviolet light.
- Add any needed suction hose support
Maintenance and Training
New installations should be initially flushed to ensure removal of any debris
that could be harmful to pumps.
Dry hydrants require quarterly inspection, testing and maintenance. More frequent cleaning may be needed at streams and ponds to make sure that silt and aquatic growth do not clog the water intake. Aquatic growth can be a special problem in ponds and in slow-moving water sources in some parts of the country. In extreme cases it may be necessary to drain a pond to control the growth. This will require careful timing and good communications to assure that other water sources are available for emergencies and that the pond will refill without undue delay.
Hydrants should be tested with a pumper once a year and backflushed as part of training exercises. Pay particular attention to safety-related features, such as warning signs and bumper guards.
Appearance is another consideration. Grass and vegetation will need to be kept trimmed. Repainting will be needed periodically. Maintaining the grounds around the dry hydrant assures better visibility in an emergency, and it will help keep good relations with the landowner.
Records should be kept of all inspections and
procedures. Keep the records available with the maps showing the location of all
installations. NFPA 1231 presents a sample maintenance record that may be
adapted and altered for local use, as well as additional design criteria.