Method of installing manhole safety steps and plugs therefor

Details Method of installing manhole safety steps and plugs therefor Method of installing manhole safety steps and plugs therefor

1979-01-30

1980-12-30

Murtagh, John E.

52 20, E02D 2912

Patent

active

042415438

ABSTRACT:
An improved method of manufacturing a concrete manhole casing and plugs for use therein. The method comprises fabricating a form for the manhole and securing a plurality of retractable arbors on the inside thereof. The arbors are extended through the form and a sealed plug is inserted on the end of each arbor. The concrete is poured into the form; vibrated and compacted. The arbors are withdrawn leaving the sealed plugs in place. The plugs carry a threading on their periphery and a novel locking structure on the inside surface.

REFERENCES:
patent: 890573 (1908-06-01), Phelan
patent: 3374859 (1968-03-01), Dobert
patent: 3436051 (1969-04-01), Nakahara

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