GSA Emails Recount Inside Story of Exploding Toilets

First time accepted submitter v3rgEz writes "Six months ago, the toilets of the General Services Administration started exploding, injuring two employees and beginning the agency's spiral down the drain of bad press (this is the same GSA now under fire for pricey Vegas conference flings). E-mails just released under FOIA now show the culprit: Compressed air + ancient plumbing + leaving it all unattended."

Comments

Re:So what?

[jbengt]

No air compressor need be connected to the water system in order to get compressed air in the system.
This has a better explanation.

Though very rare, it is not unheard of for flush valve water closets to explode. The flush valves need 20+psig to operate, and most codes allow up to 80 psig. Water is, practically, incompressible, so the release of pressure from a suddenly opening valve will create sudden acceleration that may cause "water hammer" and jerk the pipes some. But air is compressible, and if there is air in the pipes, a sudden release of pressure can cause the air to expand explosively, adding much greater acceleration and velocity to the water entering the fixture, and possibly rupturing the brittle ceramics that the fixture is made of.

In most buildings more than a few stories high, you need a pump to raise the water to the top floors and still have enough pressure. Especially in older buildings, this pump is a constant RPM centrifugal pump, which cannot adjust to the variability in flow rates, especially at times of low usage. So the discharge of the pump fills a bladder tank, which contains water on one side of the bladder and air compressed by the water on the other. The pump does not have to turn on and off all the time, because the bladder tank holds enough water and pressure to keep the water flowing for a minute or two after the pump turns off (much longer in times of low flow) and it takes a minute or two for the tank to fill to full pressure while the pump is running ( longer at times of high demand).

Apparently, in this case, the air got into the system because some part of the system failed, the water pressure dropped, and air got sucked in. It was then pressurized by the normal water pressures.

Re:For the Plumbers in the Audience

[evilviper]

But why would you have compressed air flowing into the building's water tank?

Water doesn't flow uphill, and water towers are out of fashion. An unpressurized tank at ground level would just barely dribble out of wide-open faucets on the first floor, at best. And finally, water is non-compressible, itself, so air is used as a propellant.

A water tank typically comes with an air-filled bladder taking up most of the volume. When your well pump kicks-in, water flows into the opposite side of the bladder, compressing the air behind the bladder in the process. When the tank is nearly full, the pump shuts off, and the water is under pressure. This means you have significant water pressure, and more importantly, the well pump doesn't have to turn on to maintain pressure, every single time someone uses a tiny amount of water (otherwise it would burn out the motor in short-order).

There are also (cheaper) bladder-less tank designs, where there's no hard barrier strictly keeping the air and water separate, and those are the ones that most often need to have a compressor hooked-up to them and air added, as a routine maintenance step.

http://inspectapedia.com/water/WaterTankAir2.htm

Look-up "Hydro-pneumatic tank" if you want to know more about them. If you ever get off of city water, you'll really, really need to.

http://www.highlandtank.com/PressureVessels/Products.asp?ProdID=Hydropneumatic