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In this part, we will learn about different types of manholes and manhole covers available in plumbing..
Manhole - Manhole is an underground passage where water drains away from buildings and streets, especially in urban areas. A manhole is located at the end of a storm drain pipe. In some cases they are called cover-bored holes.
P-trap Manhole
A p-trap manhole is a type of metal fitting found in the water supply system of homes and businesses. The main purpose of these manholes is to prevent sewer gas from entering the building’s water supply. A p-trap manhole consists of a vertical pipe connected to two horizontal pipes at right angles to each other. When the sewer line becomes clogged, wastewater flows out through the top horizontal pipe while gases rise up through the bottom horizontal pipe. If the water rises above the level of the bottom horizontal pipe, air enters the vertical pipe and creates a vacuum. As the water drains back down into the vertical pipe, it pulls air into the top horizontal pipe and causes the sewer gas to flow upward toward the surface.
Siphon Manhole
Siphon manholes are similar to p-traps except the siphon is inverted. Instead of having a horizontal pipe that collects wastewater at the bottom of the vertical pipe, a siphon tube extends about six inches below the bottom of the vertical tube. Sewer gases enter the siphon tube and rise upwards until they strike the end of the siphon tube. At this point, they collect inside the siphon tube where they condense to become liquid again. Because the water has no place to go but up, the water continues flowing upward into the vertical pipe. The only difference between this type of manhole and a p-trap is that a siphon manhole does not require any additional fittings.
Horizontal Trench Manhole
This kind of manhole is installed directly in the ground and receives wastewater from an underground drainage ditch. Unlike the previous two types of manholes, it does not use gravity to drain wastewater. Water fills the trench and then flows into the vertical pipe by means of a perforated plate or slotted cover. By placing the perforated plate or slot at the lowest point in the trench, the water will flow out of the perforations or slots and drain into the vertical pipe.
Pitman Manhole
Pitman manholes are similar to horizontal trench manholes except they have a longer horizontal pipe and a smaller vertical pipe. These manholes are commonly found in older buildings that have been built before the invention of the modern sewage treatment systems. To create the pit, concrete is poured over the horizontal pipe and allowed to set. After the concrete hardens, earth is excavated around the perimeter of the horizontal pipe and placed around the base of the pit. Once the pit is complete, a trap door is cut into the concrete floor to allow access to the horizontal pipe. Inside the horizontal pipe is a series of perforated plates or slots that are spaced evenly along its length. Each perforation or slot is smaller than the width of the horizontal pipe so that water will remain trapped in the area between the horizontal pipe and the wall of the pit.
Manhole covers
These are flat circular plastic covers that cover manholes and pipes. They are held down by the weight of the pipe attached to them, and they have holes at the top for drainage purposes.
Relief valves
They are designed to relieve pressure if over-pressure occurs. They work by releasing air or water from the system to prevent damage.
Siphons
Siphons are pipes that allow fluids to move from place to place without any obstructions. They are commonly used with fire hydrants to connect to a hose, nozzle, or pump.
Stopcocks
Stopcocks are valves that control flow between two conduits. They are normally placed near the end of a pipeline where users need access to the line. Stopcocks are controlled by handle devices, levers, or buttons.
Taps
Taps are the opposite of stopcocks; they open up instead of closing off. They are installed after a piping event to avoid clogs.
Shut-offs
Shut-offs are valves that close off the ends of pipelines. They are used to ensure no accidents occur while working around them.
Fittings
Fittings are pipes connectors and valves. They allow liquids to pass through them safely.
Types of Manhole covers
Concrete Manhole Covers
Concrete manhole covers are the standard model of manhole cover that is installed in most communities. It is a durable covering that lasts for decades before needing replacement. They have a thick concrete base that is poured over the top of the sewer line opening. A gasket is placed around the rim of the opening, and then the lid is put on and cemented into place.
Polymerized PVC Plumbing Covers
PVC manhole covers are plastic covered versions of the concrete style. They are similar to the concrete version except they use polymers instead of cement to hold the cover onto the pipe. They are much lighter than the solid steel type, so they are easier to install and move around. There are several different types of polymerized covers including fiberglass, acrylic, polypropylene, and nylon. These covers last longer than the concrete models, in some cases even 100 years.
Stainless Steel Manhole Covers
Stainless steel covers are also plastic covered versions of the solid metal type. They are similar to concrete covers except stainless steel is used in their manufacture. They have a smooth finish and are often glossy, making them look shiny and attractive. They are long lasting and have been known to outlast concrete covers by many times.
Solid Steel Manhole Covers
Solid steel covers are the standard model for manhole covers, and they are the heaviest and strongest covering options. They are manufactured using heavy metals like iron and steel, making them strong and sturdy. When they do break down, they are replaced, but they can last for decades if not centuries.
Fiberglass Manhole Covers
Fiberglass covers are light weight and lightweight compared to the other styles. They are not as durable as stainless steel type or concrete type covers, but they are still durable enough to keep working for decades. They are less expensive than solid metal covers, and they tend to be cheaper looking as well. Fiberglass covers may need replacing sooner than others.
Concrete Pipe Cover
This type of cover is placed over the top of a concrete pipe. These are used in residential plumbing systems where water is not running 24/7. When water does flow, the cover is removed.
Steel Manhole Cover
These are commonly called sewer covers. They are installed in places where there is no water running at all times. Unlike the concrete pipes covered earlier, these have a hole in the center that allows gas and sewage to pass through. These are often found in commercial settings.
Plastic Manhole Covers
The third option is plastic manhole covers. Like the steel ones, they also have holes in them, but their design makes them less likely to rust than steel ones. Also, since they are plastic, they do not need to be replaced after any damage occurs. However, they do require regular maintenance which includes cleaning and lubrication.
In plumbing, a manhole cover is a lid placed over a manhole drain. A plumbing system's manhole cover is typically covered by what is called a cast iron ring (or simply a ring), cast iron pot, or cast iron plate, depending upon its design. Most plumbing rings are designed to prevent water from flowing off the top of the manhole into storm drains.
There are two types of manhole covers, those that cover open pits and concrete-lined pits. A pit may have either a grate or a slab bottom. Open-pit covers are generally considered less expensive than concrete-lined covers. However, since they lack any sort of protective lining, they can allow rainwater to seep into the soil below, causing erosion and groundwater pollution. When installing a cover for an open pit, make sure that no significant amount of water will be able to flow down into the pit. To do this, use some type of drainage material at the base of the cover. If using a concrete-lined cover, make sure that the area around the manhole cover is well drained. Even if a pit is lined with concrete, moisture still needs to escape from the surrounding ground surface.
A concrete-lined cover is much easier to install than an open-pit version, but it doesn't provide as much protection against water damage. One advantage to having a concrete-lined cover is that it provides additional space between the manhole cover and the sewer pipe beneath the cover, making it possible to build a platform above the pipe. Since platforms cannot be built above a pit, concrete-lined covers often require the addition of wooden supports to hold them upright.
Manhole covers are sized according to the size of their openings. Manholes that are located near bodies of water may need to meet greater standards to prevent leakage. These covers are also required to withstand extreme temperatures, corrosion, and extreme weather conditions.
The most commonly seen designs of manhole covers are round, square, and octagonal. Round covers typically range from 45 to 70 centimeters in diameter; squares range from 30 to 60 centimeters on each side; and octagons range from 35 to 50 centimeters on each side. Many municipalities specify a minimum size requirement for manhole covers. In general, the smallest sizes are recommended for public facilities like schools, parks, and roads. Larger covers are usually specified for commercial and industrial buildings.
Round manhole covers are the cheapest option, but they are also the least effective. As mentioned previously, these covers are prone to leaking, especially if they're not installed properly. Square and octagon covers tend to leak only slightly less than round ones. The only real downside to them is weight. Heavy-duty covers are difficult to lift onto the manhole opening.
Concrete-lined manholes are ideal for underground installations. They are relatively inexpensive and easily installed without requiring special skills. Concrete covers are also extremely durable and long lasting. There are several disadvantages to using concrete-lined covers, however. Water enters the cover from several places. The first being cracks.
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