Dry Hydrants What is a Dry Hydrant? A dry hydrant is a non-pressurized pipe system permanently installed in existing lakes, ponds and streams that provides a suction supply of water to a fire department tank truck. In rural areas, a lack of water mains and pressurized fire hydrants can sometimes impair a fire department's ability to do its job quickly and efficiently. The success of a fire departments operation hinges on the distance a truck must travel to fill-up and return to the fire. In many cases these fill-up points are often long distances from the fire and the firefighters are unable to maintain an uninterrupted water source at the scene. The installation of a non-pressurized pipe system into local water sources provides a ready means of supplying water to fire engines. A dry Hydrant is more than a collection of "hardware". 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 access to water sources without delay. Depth of water at the source. Careful note should be made about the useful depth of a lake or pond, which is 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 tides, 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. Composition of the bottom material. For 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.
Ease of digging. 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. Protection the connection. A location 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. Beware of other utilities in the digging area. You must carefully check for the presence of buried lines and pipes and notify utility companies before you start digging. Dry Hydrant Advantages Knowing about a quantity of available water in area streams, ponds and lakes gives an advantage to a fire department only if the water is readily accessible. Soft or obstructed ground certainly limits access. Or, the needed water may be located so far away from where it is needed that a fire department's ability to do its job of fire control 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 numerous 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. Above Ground Installation Checklist and Instructions for Horizontal Strainers Water Source Determine the depth of water at piping entry location. In ponds, use low water level if known to ensure operation during droughts. A minimum of two feet of water over pipe is necessary to avoid cavitations. Feet or Lift Lift in excess of 15 feet needs to be avoided, a maximum of 10 feet for other than Class "A" pumps. The lift is the vertical distance from the water's surface to the hydrant outlet. Accessibility Hydrants should be located with the following considerations: All weather access. Sustained maximum grade of 8 percent. Road width minimum of 12 feet. Connection within 10 feet of the edge of road. Proper drainage of site. Proper measures to control erosion. Coordination Permission of land owner is needed if site is on private property. Local fire department needs to be notified, and should also be discussed with home owner insurance carrier. Other Considerations
Install dry hydrants as close as practical to the water source. Use as few elbows as possible, each elbow installed increases friction loss. The dry hydrant shall be fitted with an intake strainer. Purchase or construct a strainer with adequate hole openings. The total area of strainer holes must exceed 4 times the cross sectional area of the pipe. A strainer may be formed by drilling ¼ inch to 3/8 inch diameter holes in PVC pipe. Keep a minimum of one holes diameter between holes. Individual inlet hole shall not exceed 3/8 inch diameter. The end cap on the strainer should be removable, but it must be secured to the strainer. Holes in the end cap are recommended. Installation depth must be below the frost-free depth for the area. The hydrant head shall be fitted with a removable strainer. A conical strainer maximizes straining area but is not essential. 1. We feel the length of pipe should be held to around 40 feet maximum if at all possible. While the horizontal pipe should always be below water, that may not always be the case as the pipe should have a gradual slope toward the pond. During Drought conditions, long pipe lengths could lead to primer pump burnout. 2. Hydrants will need to be installed in deep water rather than in the shallow end. This is necessary due to the reach of a backhoe. On a shallow slope, the reach would exceed the 10 - foot to 12 - foot capability of most equipment. 3. Both a 45-degree or 90-degree configuration can be used to install the dry hydrant. One may be a better choice than the other depending upon terrain at the site location. 4. On short pipe installations of approximately 30 feet, we found a slight variation could be done to significantly add to the draw-down depth during drought conditions. Of course this could only be done in deep ponds, but the total pipe installation for priming would still remain within reason (40 feet maximum including 10 feet of priming suction hose). 5. Height of the dry hydrant above the ground should be approximately 2 feet or lower than the intake of the responding fire truck.
Installing Your Dry Hydrant Make sure to use 6-inch, Schedule-40 PVC pipe and fittings. Avoid allowing direct sunlight to come in contact with PVC for extended periods of time prior to installation. Epoxy paint can be applied to that portion extending above ground to aid in preventing ultraviolet degradation. A backhoe should be used to excavate a 3-foot deep trench below the water surface. 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 new correct angles of joints. If the pipe slopes it must slope up from the water source.) An important safety rule: No one should ever enter the trench! Once a trench has been dug, cut the pipe to the desired lengths and assemble. Check dry fit. Join the pipe sections with glue. Make sure you understand the technique, because timing is important. Connect all PVC pipe, fittings, and strainer together using a Tetrahydrofurance (THF) primer, and between an 800-1000 centipose viscosity PVC cement. Never use all-purpose cements to join PVC pipe and fittings. Joints must be held tightly together until both surfaces are firmly cemented. Do not disturb the joint until set occurs, which varies according to the temperature. Above 60 degrees F the recommended time is at least 30 minutes. Pressure test the joint. Only after adequate curing according to the instructions for the particular cement. Do not take short cuts! Once all components are properly affixed and allowed to dry, the entire structure should be lowered into the water in one piece. 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. The strainer should be at least 4 feet beyond the embankment. Back-fill around the pipe assembly, starting with the riser, which should be covered during this operation to prevent rock and fill from falling into the pipe, and proceed toward the water's edge. Tamp the dirt for rigid support. Mound the fill material higher for more freeze protection. Cut the vertical section (riser) of PVC pipe extending above ground leaving approximately two feet of pipe. Deburr the pipe using knife or file and cement dry hydrant head into place. 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 on a standard fire engine. That is, the pump intake must be above the hydrant connection. Smooth over the disturbed areas, and plant grass seed or other vegetation to retard erosion. Mulching helps the seed or seedlings to get established. Place a sign to identify the dry hydrant and warn against parking and other obstructions. You may want to paint the cap a reflective color for improved visibility during emergencies. If the exposed PVC is not sunscreen protected, exposed pipe must be primed and painted to prevent chemical decomposition from ultraviolet light.
Maintenance New installations should be initially flushed to ensure removal of any debris that could be harmful to pumps.