Terry Mescher
Swine production facilities have used gravity drain gutters for more than a decade. The gravity drain gutter design has evolved to provide better performance and lower maintenance to the producer, while providing a cleaner, healthier environment for both the pig and producer. These changes have led to the development of a gutter design known as a reversing hairpin gutter. This design has been used in all stages of swine production; however, poor design and/or management can prevent the gutter from cleaning properly. This factsheet is a review of the layout and management of reversing hairpin gutters for livestock producers and builders.
A reversing hairpin gutter is shown in Figure 1. The gutter is a long channel, divided down the center. Drains stopped with pull plugs are located on either side of the divider at one end of the gutter. The divider extends from the endwall near the drains, and ends 2 to 4 feet from the opposite end. These gutters are emptied by removing one of the pull plugs and allowing all the manure in the gutter to drain through one side. The next time the gutter is emptied, the other plug is removed, thus reversing the flow of manure and draining through the opposite side. Reversing the direction of flow helps to eliminate solids build-up in the gutter.
Hairpin gutters offer many advantages over other types of gutters and mechanical manure removal systems. Some of the advantages are:
Hairpin gutters also have limitations. Some of these limitations are:
Hairpin gutters should be built to the following specifications:
Hairpin gutters need a minimum manure depth of 12 inches to drain properly. Shallow gutters do not drain well and allow solids to accumulate in the gutter. Deeper gutters will develop a greater fluid pressure, which produces a faster flow. The faster flow will keep solids in the flow and carry them out of the building. In addition, a 10- to 12-inch airspace should be maintained between the manure surface and the pig floor. This airspace improves air quality near the floor and provides additional storage in emergencies. Therefore, hairpin gutters should be built with a minimum depth of 24 inches. Longer gutters should be built deeper to overcome the longer flow length. Gutters more than 50 feet in length should have a minimum depth of 36 inches and a minimum manure depth of 20 inches before draining. Accumulation of solids will be a persistent problem in gutters constructed with inadequate depth.
Solids accumulation is also a problem in hairpin gutters that are too wide. Flow in these gutters tends to channel, allowing liquids to drain away from solids in the manure. To avoid this problem, gutter width should be limited to 8 feet, creating two channels 4 feet wide. Narrower gutters still require the dividing wall in the center to create the reverse flow when emptied. If a gutter must be wider than 8 feet, install additional dividers in the gutter to maintain narrow flow channels.
Although other gravity drain gutters may slope slightly toward the drain, hairpin gutters must be constructed with a level floor. Failure to construct the hairpin with a level floor will allow the liquids to drain to the low end while the solids remain at the high end of the gutter. The result will be an accumulation of solids at the high end and a poor cleaning gutter.
The dividing wall should be located in the center of the gutter and extend from the endwall at the pull plugs, and end 2 to 4 feet from the other end of the gutter. The distance from the end of the divider to the wall should be less than the channel width of the gutter. Wider openings will allow flow to slow down at the turn and deposit solids. The divider should be built higher than the anticipated depth of manure. Divider height of 12 to 16 inches is sufficient for a 24-inch deep gutter, 20 to 24 inches for a 36-inch deep gutter.
Hairpin gutters can be easily adapted to present facilities. Hairpin gutters can be constructed on existing floors rather easily. However, construction must still provide watertight channels that are able to hold liquids in the gutter. When using concrete blocks, the interior of the gutter should be sealed to maintain a watertight channel. Leaking or weak gutter walls will only ensure improper operation of the hairpin gutter. Suitability of the floor must also be considered. A level floor and quality concrete are required.
The design and installation of the transfer system from the gutter to manure storage is important for proper operation of the hairpin gutter. Outlet piping must allow the gutter to drain quickly and allow solids to pass with liquids. Use gravity to transfer manure from the gutter to the storage or sump when possible. All drain pipe should be made of a smooth, watertight material. This will reduce flow resistance and minimize solids build-up. Pipes that absorb moisture or leak allow liquids to leave the waste stream, resulting in a thicker slurry that is more likely to clog pipes. Outlet plumbing should be a minimum of 8-inch diameter pipe. Hairpins that are 40 feet or more in length should use a 10-inch outlet pipe. These sizes will ensure a quick draining gutter and a rapid flow of wastes around the hairpin.
Plumbing from the gutter outlet to storage must have the proper slope. Shallow slopes will allow manure to become stagnant in the outlet pipe, while steep slopes will drain liquids off, leaving solids in the pipe. All outlet plumbing should be installed with a 0.5% slope for good manure flow.
Connections for the outlet plumbing can be a source of problems if designed or installed incorrectly. Sharp turns in the outlet plumbing slow down the flow of manure and may trap larger objects in the waste stream. Either of these actions may cause the outlet pipe to clog. Minimizing the number of turns and making gradual changes in direction will reduce flow obstructions. For example, using two 45-degree elbows to turn the flow instead of one 90-degree elbow creates less flow restriction to manure. All connections into this plumbing should use Wye connections instead of Tee connections to further reduce flow obstructions.
Drain plugs must keep a watertight seal. Leaking pull plugs allow liquids to continually drain out of the gutter, leaving a thick mixture of liquids and solids that will not flow in the gutter. In addition, small waste flows in outlet pipes may freeze during cold weather, reducing the flow capacity and possibly damaging the pipe. Leaking plugs may also allow gasses from the manure storage to be drawn back into the barn by the ventilation system. Safeguard the outlet plumbing from these problems by maintaining a tight seal between the pull plug and drain pipe.
Building equipment such as waterers, feeders, and ventilation systems must be considered when designing the hairpin gutter. Waterers, such as nipple waterers, that allow the animals to waste a significant amount of water work very well with these gutters. They provide waste water to the gutter to help dilute manure. Highly efficient waterers allow little wasted water to enter the gutter, thus there is little dilution of wastes. Hairpin gutters used with these waterers may require additional water for dilution of manure.
Another consideration is the type of feeder. Feeders that allow excessive feed wastage not only increase feed costs, but also add volume to the waste stream and hinder the operation of hairpin gutters. Wasted feeds absorb a substantial amount of moisture, quickly settle to the bottom of the gutter, and are difficult to keep in the waste flow. Feeder efficiency must be maintained in order to keep the hairpin gutters working properly. Wet feeders do not introduce any dilution water into the waste and should not be used with hairpin gutters unless additional water is available for dilution of wastes.
The hairpin gutter design also allows easy installation of pit ventilation, providing a healthier environment for the livestock. Several potentially harmful gasses, including hydrogen sulfide, ammonia, and carbon dioxide, can be produced by biological degredation of manure. Ventilating the pit area removes these gasses from the pit and reduces odors within the building. Pit ventilation also helps warm and dry the floor by pulling air through the floor and into the gutter.
Pit ventilation ducts can be placed directly above the gutter divider, between the divider and the flooring. However, ventilation ducts require a 12-inch air space between the manure surface and the duct. This will require an additional 12 inches or more in gutter depth depending on the flooring system and required supports. A sturdy PVC pipe will allow air to be drawn into the pipe and exhausted outside the building. These systems are usually sized to provide minimum winter ventilation rates year round. There are several other ways to ventilate the pit area. For more information on pit ventilation design, consult your local Extension agent.
When using a gutter for the first time, place 2 to 3 inches of water in the gutter to provide a lubricating layer. This keeps solids from sticking to the fresh concrete surface of the gutter. After emptying the gutter, scrape away any solids sticking to the concrete and recharge with water. Continue to recharge the gutter with water until a thin slime layer develops on the gutter surface. This thin layer will then serve as the lubricating layer. Additional water may be required to keep solids submerged.
Proper management of a hairpin gutter is critical to ensure proper cleaning and limit gas production within the building. Emptying the gutters before an adequate depth of manure is reached will result in a slow flow and poor cleaning. While deeper manure depths allow more time for gasses to be released, cleaning action of the gutters is much improved. Store manure in the gutter to a minimum depth of 12 inches before draining to obtain the cleaning action required in a hairpin gutter. Manure depths greater than 12 inches create a larger waste flow and a greater cleaning effect.
Maintain a liquid surface over the manure in the gutter to reduce the amount of gasses released and promote proper cleaning of the gutter. Water absorbs ammonia released from the manure, thus a liquid surface acts as a seal over the wastes. Additional water also further dilutes the manure, improving the flow through the gutter and outlet plumbing. This may be accomplished with water wasted from waterers in the building, or may have to be added to the gutters.
Outlets that allow wastes to rapidly exit the building will keep more solids suspended in the waste flow. Keep outlet plumbing clear of debris and settled solids. In addition, if several gutters drain into the same outlet pipe, drain one gutter at a time to maintain a high flow rate of wastes leaving the gutter.
Hairpin gutters are a convenient, low cost way to transport manure out of swine production facilities. Hairpin gutters require no energy inputs or large dilution volumes to operate properly. However, hairpin gutters must be designed, built, and managed correctly in order to operate properly. Contact your local Extension agent for more information on the design and management of hairpins or other gravity drain gutters.
Meyer, Daniel J., Gravity Drain Gutter Systems, PIH-95. Pork Industry Handbook.
Meyer, Vernon M., Flat Bottom Gravity Drain Gutter for Swine Manure, Pm-1377. Iowa State University Extension.
White, R. K., Narrow Gutter/Gravity Discharge Systems for Handling Swine Manure, AEX-702. Ohio State University Extension.
Glen Arnold, Ohio State University Extension, Putnam County.
Richard Stowell, Ohio State University Extension, Department of Food, Agricultural and Biological Engineering.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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