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wht is the purpose of holes in man hole covers
- Thread starter DUNBAR87
- Start date
They could also be for air ingress and egress if the manhole covers a pit where an air valve on a pipeline is placed. Otherwise the air valve wont function or the cover could be blown off.
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His Holiness the Dalai Lama.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
For whatever it is worth I believe at one time there was quite a bit of discussion and indeed maybe some practice in areas regarding “holes” in manhole covers (beyond modern “pick holes” in gray or ductile cast iron covers) e.g. as mentioned in ASCE Manual #37, “Design and Construction of Sanitary and Storm Sewers” (1982), e.g. “…ostensibly to aid ventilation”. However, the 1982 version of this manual also provided several possible hints as to why this and other publications (e.g. ASCE MOP No. 60/WPCF MOP No. FD-5, “Gravity Sanitary Sewer Design and Construction” 1982) have not really promoted this as a function of manhole covers in recent years. These hints included the following:
1. “At most, a ventilated cover may permit partial drying of the manhole but it cannot affect appreciably conditions in the pipe between manholes.”
2. “In exceptional conditions where ventilation may be needed to relieve pressure differences or prevent oxygen depletion, special vents should be provided.” (I believe Mr. stanier’s application might fit this bill, and I think “special vents” in that context were probably meant to potentially refer to structures beyond simple cored or drilled holes in the cover.)
3. “On sanitary sewers, holes in the covers allow the undesirable entry of stormwater and grit, as well as the mischievous entry of sticks; and they favor the escape of sewer air, causing odor nuisances.” (i.e. holes are likely to increase volume to be treated, particularly in low lying areas or areas subject to flooding etc., where alas many sewers are wont to be!)
For these reasons I believe modern trends are more likely to want tighter overall systems and manholes, including covers.
1. “At most, a ventilated cover may permit partial drying of the manhole but it cannot affect appreciably conditions in the pipe between manholes.”
2. “In exceptional conditions where ventilation may be needed to relieve pressure differences or prevent oxygen depletion, special vents should be provided.” (I believe Mr. stanier’s application might fit this bill, and I think “special vents” in that context were probably meant to potentially refer to structures beyond simple cored or drilled holes in the cover.)
3. “On sanitary sewers, holes in the covers allow the undesirable entry of stormwater and grit, as well as the mischievous entry of sticks; and they favor the escape of sewer air, causing odor nuisances.” (i.e. holes are likely to increase volume to be treated, particularly in low lying areas or areas subject to flooding etc., where alas many sewers are wont to be!)
For these reasons I believe modern trends are more likely to want tighter overall systems and manholes, including covers.
Holes have also come up in concurrent discussion at (Some suggest holes should make a “comeback”.)
dicksewerrat
Civil/Environmental
Have you ever tried to open a MH without pick holes, alone and only a pick in the car?
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
Many years ago I was told that the holes in gravity sewer lines were there to compensate for for changing flows or levels especially large diameter lines.
Addenda:
In front of the old home place there is 12' diameter brick gravity sewer that comes from Birmingham, Alabama. The manholes are spaced quite close to gather as I could see three standing on sidewalk in front of the house. While walking to school one morning the air was still enough that you could get whiff of H2S as you passed by a manhole. That morning as I got to the one in the street in front of the school and about 15' from the manhole there was an explosion in the sewer line which lifted every cover in sight to way above he 50' telephone poles. The one by me came down through the telephone wires and took out about 1/3 of them. from that time on I avoided hanging around any sewer manholes.
Addenda:
In front of the old home place there is 12' diameter brick gravity sewer that comes from Birmingham, Alabama. The manholes are spaced quite close to gather as I could see three standing on sidewalk in front of the house. While walking to school one morning the air was still enough that you could get whiff of H2S as you passed by a manhole. That morning as I got to the one in the street in front of the school and about 15' from the manhole there was an explosion in the sewer line which lifted every cover in sight to way above he 50' telephone poles. The one by me came down through the telephone wires and took out about 1/3 of them. from that time on I avoided hanging around any sewer manholes.
Sanitary manholes are no longer constructed with open grates. Since all manholes now are essentially sealed, how would you expect the venting to occur?
Note that gravity sewers do not operate with full pipes, there is air above the fluid.
Note that when you drive down a northern residential street in the winter, you can observe the venting and condenstation.
If you remain unconvinced, perhaps you should consider reviewing a book like Metcalf & Eddy's Collection & Pumping of Wastewater. The link contains a pertinent section discussing house venting.
Note that gravity sewers do not operate with full pipes, there is air above the fluid.
Note that when you drive down a northern residential street in the winter, you can observe the venting and condenstation.
If you remain unconvinced, perhaps you should consider reviewing a book like Metcalf & Eddy's Collection & Pumping of Wastewater. The link contains a pertinent section discussing house venting.
johnabcd
Bioengineer
- Jun 3, 2011
- 2
- 0
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These days most of the manholes are completely sealed packed. We have generally circular manhole covers. And about the holes, the presence of holes make the air pass through them so that the pressure created by the gases generated from the sewage do not exceed.
Thanks Bimr for sharing a great stuff with all.
John
Thanks Bimr for sharing a great stuff with all.
John
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