Hey there, it’s Jake, from that small manufacturer you might have seen popping up at utility expos and industrial supply trade shows over the last few years. If you’ve ever ordered round manhole covers for a road project, a municipal sewer upgrade, or even a big commercial parking lot, you know that question’s been bouncing around your specs team for a minute: do round manhole covers actually need that edge seal around the rim? I get it—you’re trying to cut costs, keep install time low, and make sure every part of your project works for 20, 30, even 50 years. I’ve heard every argument on both sides, and over the last seven years, I’ve worked on covers that go in everything from downtown Chicago’s subway tunnels to small rural town water mains, so I’m here to break this down like we’re talking over a coffee (or a toolbox, if you’re on site right now). Round Manhole Cover
First, let’s get the obvious out of the “why round manhole covers are standard” stuff—because that’s the baseline for why edge sealing even comes up. Everyone’s heard the old joke: a round cover can’t fall through a round hole, right? If you flip it 90 degrees, the diameter is the same, so it won’t tip into the shaft. Square or rectangular covers? Their diagonals are longer than their sides, so they’re a fall risk. That’s non-negotiable for utility teams—safety, liability, and OSHA standards don’t mess around with that. So we all agreed on round decades ago, now we’re arguing about the edges.
Let’s start with what happens if you skip the seal. For a lot of small projects, especially temporary ones or areas with mild weather, you might think: it’s a heavy cast iron cover sitting on a cast iron frame, right? The weight alone will keep water, debris, rodents, or even sewer gasses from getting through. But let’s talk about real world conditions. I remember three years ago, we shipped a batch of 24-inch solid top round covers to a small township in northern Ohio. They were in a hurry to fix a collapsed sewer line before the first big spring thaw, so they skipped the edge seal to save two hours on install and $1.20 per cover in materials. Six months later, their public works director called me in a panic—half the covers had shifted just enough to let melting snow, road salt, and silt seep into the manhole shaft. The silt built up so much that the level sensor they installed for water flow testing was reading wrong, and road salt was corroding the cast iron frame from the inside out. By the time they fixed it, they’d spent more in emergency repairs, sensor calibration, and lost project data than they would have on the edge seals for all 120 covers.
Wait, but what about different types of manhole covers? Because not all round covers are the same. We make three main lines: cast iron heavy-duty for highway and mainline sewer, ductile iron medium-duty for residential streets and parking lots, and composite plastic for light-duty pedestrian areas or utility vaults. The edge seal needs are totally different for each. For heavy cast iron covers that get 18-wheeler traffic driving over them? The weight is around 50 to 100 pounds, right? When a truck hits the cover, it doesn’t just sit there—it bounces a tiny bit, shifts micro-millimeters on the frame every time there’s a load. Over a year, that tiny movement creates gaps. Road grit gets in, water seeps, gasses escape. For ductile iron, which is lighter (around 30 to 60 pounds) and often used in areas with more foot and residential traffic, that movement is even worse because the cover is thinner and has more give. We had a client in suburban Atlanta a couple years back who used un-sealed ductile covers for a new neighborhood development. By the end of the first winter, they’d had 17 calls about sewer odor coming up through the manholes, plus sediment in the lines that required a jet clean two years early. The composite covers? Even though they’re light, their surface is smoother, and rainwater runoff picks up oil from parking lots and chemicals that can seep through gaps. We always recommend a closed-cell foam or EPDM rubber seal for composites because they don’t rust, so the seal is the only barrier between the environment and the shaft.
Now, let’s talk about the counterargument, because I don’t want to paint edge seals as a “no-brainer” for every job. I’ve had clients say, “We’ve been doing this for 40 years without seals, why change?” And they’re not wrong—for low-traffic, indoor applications, like basement utility vaults or access panels in a factory basement, you can often get away with no seal. No one’s driving over that, no road debris, no heavy temperature swings to make metal expand and contract. But outdoor applications? Especially in places with extreme heat, cold, or frequent freeze-thaw cycles? That’s where the seal becomes non-negotiable, not optional. Metal expands when it’s 100 degrees in July, contracts when it’s 10 below in January. Over time, that thermal cycling makes even the tightest fit between cover and frame develop a gap. If you have a seal, that flexible material moves with the metal, so the gap never opens enough for debris or water. For example, in Minneapolis, we did a test last year: we put three identical 36-inch heavy-duty covers, two with seals, one without, on a test track that simulates 10 years of highway traffic. After 100,000 passes, the un-sealed cover had a 1.2 millimeter gap around the edge. The sealed covers had a gap of less than 0.1 millimeters—almost nothing. That might sound small, but over time, that’s enough for road salt and silt to get in, accelerate corrosion, and reduce the lifespan of the cover by years.
I’ve also heard people say seals get damaged easily, or they add extra labor to install. Let’s address that. When we add a seal to a round manhole cover, we pre-groove the edge of the cover at the factory, so the seal is a press-fit or bonded in during manufacturing. That means when our installers show up, they just set the seal on the frame, lower the cover on top, and it’s done. No extra steps, no messing with cutting or adjusting the seal on site. The average install time for a sealed cover is 10% longer than an un-sealed one—wait, that’s like two minutes, not hours. I’ve had clients tell me that the long-term savings are worth way more than that tiny extra time. And as for damage? We use EPDM rubber seals, which are UV-resistant, tear-resistant, and can last as long as the cover itself. I’ve replaced covers after 25 years, and the seal was still intact enough to reuse if the cover wasn’t damaged.
Wait, what about round covers that have a lifting eye, or a vent for sewer gasses? A lot of people ask if the seal would block that. No, not if you spec the right seal. We make custom seals for every type of cover: solid top, vented, lifting eye, even specialized ones for gas or electrical vaults. If you need a vent, we cut a matching channel in the seal so it doesn’t block airflow. If you have a lifting eye, we notch the seal so the metal bar of the eye sits in the notch, so you can still lift the cover without prying it. We don’t do one-size-fits-all here, and that’s a big reason why we stand behind our covers.
Let’s talk about compliance, too. A lot of municipal standards now require edge seals for manhole covers in high-traffic areas, coastal zones (where saltwater corrosion is a huge issue), or areas with frequent heavy rainfall. OSHA’s fall protection guidelines for utility worksites also note that un-sealed covers are more likely to shift, creating a tripping hazard for workers. I’ve seen towns get fined for un-sealed covers that caused environmental contamination—like when runoff from a construction site got into a sewer line because of gaps in un-sealed covers, leading to a spill that required a cleanup. That’s a cost no one wants to deal with, especially when a $1.50 seal per cover would have prevented it.
Now, I’m not saying you should put seals on every round manhole cover that’s ever made. If you’re working on a temporary access panel inside a building that’s only going to be there for six months, no seal is needed. If you’re in a warm, dry climate with almost no freeze-thaw cycles and light traffic, you might get away with skipping it. But for 90% of the projects we work on—highway, residential streets, municipal sewer lines, commercial parking lots—edge seals aren’t an extra expense, they’re an investment.
Let me give you a real example from last year. We had a client in Denver who was working on a 50-street rehabilitation project, totaling 2,200 round manhole covers. They initially estimated no edge seals would save them around $3,300. Six months after install, they started getting complaints from residents about sewer odor, and their public works team found that 18% of the un-sealed covers had shifted enough to let gasses escape plus silt buildup in the lines. They spent $12,000 on emergency jet cleaning and cover adjustments, plus another $2,700 to install seals on the remaining covers. By the end of the year, they’d spent more on fixing the un-sealed covers than they would have spent on seals for all of them.
The thing is, when you buy round manhole covers, you’re not just buying a piece of metal to put in the ground. You’re buying something that has to last decades, handle weather, traffic, and all the messy stuff that comes with being a part of the infrastructure that holds cities and towns together. Edge seals aren’t a trick or a marketing ploy—they’re a practical part of making that cover work as well as it can, for as long as it needs to. If you skip them, you’re setting yourself up for extra costs down the line, more maintenance, and more headaches for your team and the people using the roads or buildings.
At the end of the day, the question isn’t “do round manhole covers need to be sealed around the edges?” It’s “do you want your manhole covers to work as long as they should, without extra costs and headaches?” For most projects, the answer is yes. If you’re still on the fence, whether you’re a municipal engineer, a construction foreman, or a facilities manager, we’re here to help. We can walk you through the right seal type for your cover, your area, and your project, no sales pitch, no pressure. Just real advice from people who’ve been in this business long enough to know what works and what doesn’t. If you have questions about specs, pricing, or even our test data, reach out to our team to talk through your project needs.
Manhole Cover References:
- American Society for Testing and Materials (ASTM) International. Standard Specification for Manhole Frames and Covers. ASTM C478-21, 2021.
- National Association of Corrosion Engineers (NACE). Corrosion Control for Underground Infrastructure. NACE SP0169-2013, 2013.
- Federal Highway Administration (FHWA). Manhole Cover and Frame Performance in Highway Applications. FHWA-RD-19-007, 2019.
- Occupational Safety and Health Administration (OSHA). Walking-Working Surfaces: General Requirements. 29 CFR 1910.22, 2022.
Wenzhou Shunzhan Fluid Equipment Co., Ltd.
Address: No. 15, Zhabei Road, Cangning Village, Shacheng Street, Wenzhou Economic and Technological Development Zone
E-mail: chengzhan@263.net
WebSite: https://www.shunzhanfluid.com/
