Why is a Manhole Round?

By OPW | Aug 29, 2012

If you Google the top ten toughest job interview questions, the question that most frequently appears is, "Why are manhole covers round?" And while the answer to this question has stumped job applicants for years, it certainly would make them take pause the next time they pulled their vehicle into a service station and heard that familiar "clank" while driving over one.

However, unless you happen to be one of those unlucky job applicants, the rest of us never give the manhole covers we drive and walk over at the service station a second thought. But in actuality, manholes are a vital piece of fueling equipment and provide access from grade level to underground equipment, including tank sumps, tank riser pipes, monitoring equipment, submersible pumps, valves and piping connections. Manholes also help ensure that the fuel tanks located beneath the service station are receiving the correct kind of fuel.

In addition to being a valuable piece of fueling equipment, there is also a wide variety of manholes that you will come across in a service station, including:

  • Composite Manholes – Designed for use in many service station, commercial and industrial driveway applications to provide easy and safer access to tank sumps and other underground equipment
  • Cast Iron and Fill Boxes – These manholes are ideal for connecting underground tank lines directly to the surface without sump enclosures
  • Steel Manholes – Designed to provide access to all types of underground equipment, including vapor recovery connections, UST monitoring equipment and submersible pumps
  • Monitoring Well Manholes – Designed for monitoring and observation in applications where limited access and clear identification are essential

Manholes the OPW Way
When it comes to manholes, nobody in the industry does it better than OPW. And recently, OPW Fueling Containment Systems announce the release of a new Watertight Model of its 104 Series Cast Iron Manhole. Heavily ribbed to ensure maximum load bearing capacity, the 104 Series Manholes are ideal for connecting underground tank lines directly to the surface without sump enclosures. A sturdy, steel skirt extends nearly a foot below grade to ensure trouble-free installation in deep concrete, and optional skirts that extend a full 19¼" below grade are available in 12" and 18" diameters for sandy soil locations. A variety of features are available on the 104 Series Manhole, including a watertight model that makes it an ideal choice for a variety of tough applications.

The new watertight manhole model includes:

  • Full-size internal diameters for maximum access and working area
  • Highway 20 Rated (H20) – All OPW manholes exceed the requirements of the Highway 20 rating
  • Cast-in, non-skid finish on cover
  • Sturdy, extra long steel skirts available for 12" and 18" manholes
  • Individually boxed for ease of handling

For more on OPW, please visit us at the 2012 PEI/NACS Show in Booth #4017.

As far as an answer to why manhole covers are round, theories vary, but the most accepted response is that a round manhole cover cannot fall through a circular hole, whereas a square or rectangle manhole cover may fall into the hole.

What type of manholes is your operation utilizing?

We'd love to hear from you!