Municipal Castings Glossary
Bearer bar: Side frame only. Used in pairs on ducts and channel gratings.
Captive hinge: Integral hinge which prevents total removal of cover or grating.
Chequer plate: Non-skid pattern on top surface of covers.
Clear opening: Nominal unobstructed access opening in a frame neglecting minor incursions.In the case of duct covers & linear gratings the clear opening is the duct or channel width x the unit length x the number of units used. (See illustration `duct covers`).
Corbeling: Staggering of brickwork below frame to reduce final gully/manhole opening size to that of the frame.
Double seal: Traditionally double vertical tongue in groove relationship between cover with double rim and frame with double groove.Allows double grease seal against egress of odour limits ingress of rainwater.
Double triangular: Covers or gratings formed from two triangular sections giving stable seating under load and a non-rock performance.
Duct cover: Covers and frames where frame is two bearer bars (side frames) enabling units to be fitted end to end to cover cable or pipe ducts where access may be required at any point
End hinged: Hinge at end at 90deg to kerb. See LEFT and RIGHT HAND OPENING.
Flat top: Cover top surface is all iron i.e. non-recessed.
Kerb hinged: Hinge located at and paralell with the kerb.
Keyways (Closed): Blind lifting holes in covers for lifting keys which prevent ingress of dirt and water.
Keyways (Open): Lifting holes in covers for lifting keys.
Left hand opening: Hinged grating that opens from the left when viewed from the pavement. Standard for the U.K. on two-way roads as would be closed by oncoming traffic.
Loosely coupled: The two half covers/gratings of double triangular units are connected together loosely by nuts & bolts or pins. This prevents the units being dropped in the shaft during lifting and, being a loose connection, still allows the two half covers/gratings to bed indepentently and retain their non-rock facility
Non-rock: Cover/grating and frame design which gives quiet stable seating by means of 3 point non-rock seating, i.e. double triangular.Machined seatings (Pametic) and gasket seatings (Ax-S 400) are other non-rock designs.A requirement of BS EN124 Class D400.
Pressure tight: Cover and frame which can withstand internal pressure as in surcharged drain systems.Obtained by use of bolt down MSG sealplate as in Inter-Ax, machined seating as in Pametic or units with sealing rings and bolt down cover as with Pamtight.No pressure tight unit can be sealed retrospectively.
Prising slot: Slot in cover edge or occasionally on inside of frame that allows the use of a crow bar to loosen covers before removal.
Recessed cover: Top of cover recessed to allow infilling with a chosen material, concrete, quarry tiles etc., usually to match the surrounding area. Note most iron covers have a shallow recess and may not be suitable for use with pavior blocks.
Safety grid: A fabricated galvanized mild steel grid, which normally drop fits on the frame below the cover to prevent covers and other objects being dropped into the shaft.
Seal plate ( Bolt Down ): Galvanized mild steel plate, fitted with a gasket, which is bolted to the frame to prevent egress of odours and which may limit the ingress of water.Capable of withstanding a back pressure of 0.5bar.Cannot be fitted retrospectively.
Seal plate ( Push Fit ): Glass re-inforced plastic (GRP) plate, fitted with gasket, which is a push fit into the frame and prevents egress of odours and which may limit the ingress of water and, especially in countries with high ambient temperature, acts as a barrier against the corrosive properties of the sewer gases. Not capable of sealing under backpressure. May be fitted retrospectively.
Sealed: Covers and frames which are sealed in some way to at least prevent the egress of odours from the sewer.There are different methods of sealing and these give varying standards of performance.See DOUBLE SEAL, SINGLE SEAL, SEAL PLATES and PRESSURE TIGHT.
Seating: Bearing /contact area between cover and frame. Also type of contact:
• Three point seating
• Non-rock seating
• Machined seating
• Gasket (rubber) seating
Single piece: Cover/grating comprises one piece.
Single seal: Traditionally single vertical tongue in groove relationship between cover with single rim and frame with single groove.Allows single grease seal against egress of odour limits ingress of rainwater. Also see SEAL PLATE.
Slide out: Cover removed by lifting one end and then sliding out rather than direct vertical lift.Can reduce the effort of removal.
Ventilated cover: Cover with slots or holes that allow free circulation of air within the shaft and help prevent pressure build up. Minimum vented area is specified in BS EN 124.
Waterway area: Free area of grating which allows the passage of water (total area of slots).