# nitrogen tanks on NYC sidewalks **URL:** \ **Category:** Factual Questions\ **Created:** [August 11, 2005, 12:29am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532 "2005-08-11T00:29:20Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![abby](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@abby](https://boards.straightdope.com/u/abby)\ **Post date:** [August 11, 2005, 12:29am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/1 "2005-08-11T00:29:20Z")
Hiya Visiting New York City this week, and I saw a bunch of stainless steel nitorgen tanks near power poles on sidewalks, with thin red hoses going a few feet out on to the road, then down into a manhole. What are these for? a ---
**Author:** ![abby](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@abby](https://boards.straightdope.com/u/abby)\ **Post date:** [August 11, 2005, 12:32am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/2 "2005-08-11T00:32:08Z")
Of course, I meant Nitrogen. a ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [August 11, 2005, 2:02am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/3 "2005-08-11T02:02:22Z")
> [@abby](#): > > HiyaVisiting New York City this week, and I saw a bunch of stainless steel nitorgen tanks near power poles on sidewalks, with thin red hoses going a few feet out on to the road, then down into a manhole. What are these for? To pressurize the phone line with dry nitrogen and keep out moisture till repairs can be made or the cable replaced. Insures integrity of lines and maintains service. ---
**Author:** ![abby](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@abby](https://boards.straightdope.com/u/abby)\ **Post date:** [August 11, 2005, 2:06am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/4 "2005-08-11T02:06:39Z")
**spingears** , asked and answered, thank you! ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 11, 2005, 2:07am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/5 "2005-08-11T02:07:21Z")
> [@spingears](#): > > To pressurize the phone line with dry nitrogen and keep out moisture till repairs can be made or the cable replaced. > Insures integrity of lines and maintains service. Almost. The dry nitrogen tanks are normally connected _after_ a repair or splice has been made, to drive out any moisture which may have condensed inside the cabling while it was exposed. Once the nitrogen has done its job, the tanks are disconnected and the pressure in the cables is maintained by dry, filtered air pumped in from the central office. Moisture doesn’t physically affect the cabling - the plastic insulation is pretty well impervious to anything - but it affects transmission quality in various ways. ---
**Author:** ![glilly](https://avatars.discourse-cdn.com/v4/letter/g/48db29/32.png) [@glilly](https://boards.straightdope.com/u/glilly)\ **Post date:** [August 11, 2005, 3:12am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/6 "2005-08-11T03:12:01Z")
> [@Q.E.D.](#): > > Almost. The dry nitrogen tanks are normally connected _after_ a repair or splice has been made, to drive out any moisture which may have condensed inside the cabling while it was exposed. Once the nitrogen has done its job, the tanks are disconnected and the pressure in the cables is maintained by dry, filtered air pumped in from the central office. Moisture doesn’t physically affect the cabling - the plastic insulation is pretty well impervious to anything - but it affects transmission quality in various ways. Holy crap! Are you telling us that the phone cables have dry air running through them from the offices? Surely this is flowing air to make up for leaks. What is the flow rate from the main office? Are there dry air substations? What is the pressure in the lines? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 11, 2005, 3:23am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/7 "2005-08-11T03:23:38Z")
Sure, there’s small leaks, typically pinhole-sized, so there must be a constant flow of air in to maintain pressure. I don’t know specifically what the pressure level is, but it’s low; probably only a few PSI. The central offices each have a special pump with filters, dehumidifiers and whatnot to clean and dry the air and feed it to the cabling. I don’t know how the longer trunk lines are handled, but there are usually repeater substations on these, to periodically amplify the signals to make up for line losses, and it seems likely that these could have the pumps, as well. Some older lines are not continuously pressurized and have to be periodically dried with either compressed or liquid dry nitrogen whether repairs are made or not. ---
**Author:** ![Metacom](https://avatars.discourse-cdn.com/v4/letter/m/ecae2f/32.png) [@Metacom](https://boards.straightdope.com/u/Metacom)\ **Post date:** [August 11, 2005, 3:25am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/8 "2005-08-11T03:25:18Z")
> [@glilly](#): > > Holy crap! Are you telling us that the phone cables have dry air running through them from the offices? Surely this is flowing air to make up for leaks. What is the flow rate from the main office? Are there dry air substations? What is the pressure in the lines? Yup! In every central office I’ve ever been in (a couple dozen?) there was a compressor, tanks, and an air drier immediate above the cable vault (where all the big cables enter the CO and get routed up to the frame). I have no idea what the flow rate is, but there were certainly gauges on the equipment. Maybe someone who currently has access to a CO can give you more info. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 11, 2005, 3:32am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/9 "2005-08-11T03:32:09Z")
The exact flow rate is going to depend on the number and size of leaks in the cabling. The more leaks and the larger they are, the more rapidly air needs to be pumped in to maintain the pressure. I’ll see if any of my telecom references have any data on cable pressure levels. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 11, 2005, 3:35am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/10 "2005-08-11T03:35:48Z")
> [@](#): > > Copper cables used in the Telecom industry use the latest developments in technology to deliver high speed internet access and broadband services. These cables develop holes in the sheath leading to deterioration and replacement of cable lengths. When pressurized with sufficiently dry air, these cables will provide decades of reliable use in return for very low maintenance costs. Drallim dehydrators used in such networks create adequate air pressure, volume and dryness in the cable with pressurized air. Drallim has dehydrators of different capacities to meet all requirements of the industry. The dehydrators are available from 1 to 80 outlets with dry air delivery from 30 to 185 Cubic Ft/hr at an output pressure of 3 to 15 psi. From [here](http://www.telectron.co.ae/telecom.htm), a manufacturer of the aforementioned equipment. Looks like between 3 and 15 PSI is typical. I’ll go out on a limb and say typically 9 PSI. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [August 11, 2005, 4:48am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/11 "2005-08-11T04:48:13Z")
I’m a bit puzzled. I’ve never seen stainless steel tanks for pressurized gas just the insulated cryogenic tanks for liquid nitrogen which I would think would not be suitable for pressurizing phone lines. Am I missing something? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 11, 2005, 4:58am UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/12 "2005-08-11T04:58:35Z")
> [@Padeye](#): > > I’ve never seen stainless steel tanks for pressurized gas just the insulated cryogenic tanks for liquid nitrogen which I would think would not be suitable for pressurizing phone lines. I’ve seen both. The liquid nitrogen tanks work in a similar way: the liquid nitrogen evaporates gradually, keeping the pressure maintained. It’s just a way to store more nitrogen in the same volume, is all. ---
**Author:** ![Bookkeeper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bookkeeper/32/281_2.png) [@Bookkeeper](https://boards.straightdope.com/u/Bookkeeper)\ **Post date:** [August 11, 2005, 3:40pm UTC](https://boards.straightdope.com/t/nitrogen-tanks-on-nyc-sidewalks/316532/13 "2005-08-11T15:40:29Z")
Mnay, many years ago when I was an army reservist, I worked full-time for a while at CFB Carp, which was then the location of the nuclear war bomb shelter and command centre for the Canadian government. While we were waiting for it to be put to its planned use, it was used as a communications centre. The radio antennas were all located at widely dispersed sites (to survive the A-bomb blast) and were connected through pressurized cables to the base. We would spend about half our time driving back roads to isolated manholes and humping fresh nitrogen tanks into them to keep the lines pressurized.