YOUR COMPREHENSIVE GUIDE TO SELECTING THE RIGHT MANHOLE COVERS.
Manhole covers can be found pretty much everywhere these days, you name it; there’s probably a manhole cover in it or nearby.
Despite being relatively common and widespread, no-one really takes an interest in manhole covers (surprisingly). Well, that is unless you’re the Labour party leader Jeremy Corbyn, who apparently enjoys observing and collecting manhole covers… But that’s another story.
Because of this, when it comes to selecting a suitable manhole cover, most of us are left in the dark, quite literally, so here’s a few handy manhole tips to help you out.
What Are They?
It’s pretty obvious, but a manhole cover is essentially a removable plate forming the lid over the opening of a manhole. This prevents anyone or anything from falling in, as well as keeping unauthorised people out.
What Size Do I Need?
This is often a source of misunderstanding, but manhole covers are manufactured and listed by their ‘clear opening size’, which is essentially the size of the hole that the cover is to span, not the actual diameter of the manhole cover.
For example, a manhole cover listed as 600 x 450mm will more than likely have an overall measurement of nearer 650 x 550mm, but it will be designed to fit a hole size of 600 x 450mm, therefore it’s size will be listed as 600 x 450mm.
It is important that the correct size is sourced, too small and the manhole cover will likely fail. Having the cover too big can be ok, unless the cover has reinforcing on its underside. However its best practice to source the correct sized cover.
Types Of Manhole Sealing
No seal – The cover is usually just placed on top of its frame and that’s that. It is normally heavy duty, cast iron or slide out covers that are unsealed.
Single seal – Most manhole covers manufactured these days are single sealed. It is essentially a tongue and groove joint which is airtight when sealed. The cover surround is normally filled with grease which helps form the seal.
Double seal – This is simply a double tongue and groove joint, which, as you would expect, forms a more comprehensive seal. Again this form of seal prevents air from escaping, providing the manhole is not under pressure. The double seal is often used when foul drainage manholes are situated within buildings.
Types Of Manhole Cover
Solid top (flush): These covers fit flush with the ground and the whole of the cover is visible.
Recessed: Recessed covers have an insert tray which is used where block paving, tiling or any type of infill is required. This leaves only a few mm of the frame visible.
Cast & Ductile Iron: similar to solid top flush fit covers, although there is a sub category for gully gratings etc.
Weight Classes
Steel manhole classifications:
A15 – For areas only accessible to pedestrians and pedal cyclists.
B125 – Suitable for driveways and areas accessible by vehicles.
C250 – Suitable for areas with slow moving heavy traffic.
D400 – Suitable for areas with fast moving heavy traffic – eg carriageways.
Iron manhole classifications:
Class A – suitable for pedestrian usage.
Class AA – suitable for vehicular traffic up to 5 tonnes.
Class AAA – suitable for vehicular traffic up to 10 tonnes.