Watch it happen!
Thanks for the illustration. It sure shows how important admitting air can be. It reminds me of a simple experiment in physics. You take a gallon can with a screw top, put a little water in it and boil the water until the can is filled with steam. Then take the can off the fire and screw on the top. You can run cold water over it or just let it stand and watch the slow collapse as it implodes.
WHOOPS! posted to the wrong thread! Sorry about that.
Well. I do have something to say here too… the collapse is often NOT “slow”. Once the stress reaches a certain point the vessal will start to collapse and once over the starting point, it occurs very rapidly.
I didn’t intend to suggest that a tank car which is drained without allowing air to enter would collapse slowly. Rather, in the experiment I describe if the steam filled can is allowed to cool slowly the collapse will be slow because it takes the steam a while to condense. When a tank car is incorrectly drained the vacuum is produced very quickly so I would expect the collapse to be fairly quick.
I am surprised that no fail safe system to prevent such a collapse has been found. Tank cars have been around for a pretty long time now so the problem must not be new.
Most nonpressure cars equipped with bottom outlets have a “vacuum breaker” valve for exactly that reason.
Mac
Since pressure relief valves are commonly used even on hot water heaters it did seem to me that relieving the vacuum inside a tank car should not be difficult. After all, the problem is excess pressure in the atmosphere.
What diameter outlet or hose ?
The 10 psi would greatly speed up the process, too. The average pressure of the syrup in an 8 ft. diameter (guess) tank from gravity only would be on the order of 2 psi*, so with the 10 psi added that’s 6 times greater.
*Assuming corn syrup has roughly the same density as water - 62.4 lbs. per cubic foot / 144 sq. inches per square foot = 0.43 psi per foot of depth, so under gravity only (no air pressure added) the pressure at the outlet would vary from about 3.5 psi when the 8 ft. diam. / high tank is full to 0 when it is empty. No idea on the viscosity or ‘flowability’ of the corn syrup, or at what temperature, etc.
- Paul North.
Sparing everyone the math, and ignoring friction, ‘head losses’, ‘edge’, orifice, or ‘inlet control’ effects, etc.:
A 6" diam. outlet has an area of about 0.20 sq. ft.
A 10 ft. diam. tank at half-full (5 ft.) of water at normal temps. will discharge at about 18 ft./ sec. (per Bernoulli’s equation).
With various measurement unit conversions, that works out to about 1,600 gals. per minute, if I’ve done the basic math right this late at night.
So to unload that 30,000 gal. tank car through a single outlet would take about 20 mins., more or less.
Details and refinements, etc. are invited.
- Paul North.
The first photo is the result of a plant worker steam cleaning a tank car, exiting the car and closing the manway hatch, without opening the tank car drain and safety valve.
The video is from Brazil, it is a training tape made for plant workers showing what happens when a non-pressure differential tank car is drained without opening the safety valve.
All US tank cars that carry pressurized gas and liquids have what Mac says, a vacuum breaker valve, which is a one way valve that allows outside air to enter the car.
High Fructose Corn Syrup (HFCS) is actually quite a bit more dense than water. Not all HFCS in commercial use is exactly the same, but generally it is of similar density to honey. Roughly, water is 8 lbs per gallon, honey is 12 lbs per gal. A typical HFCS product is about 11.5 lb per gallon.
(I am also a beekeeper, and honey, sugar, and substitutes are hot topics on beekeeping forums. [:-,])
Stuff I haul every now and then I might get 2 loads a month has the consistency of 90W Gear Oil when Cold. Compared to the Acid I haul it is a Very and I mean VERY Stable load inside those Smooth Bore Tankers. We use a Standard 4 Inch line to Drain the trailer and no more than 10 PSI otherwise the relief Valve will pop and then you got a Problem. WPG is right around 12 how we haul so much to the Factory is Simple they do not have a Direct Rail Unload Point at their Factory. However my Boss has a Trans Shipment Point less than 20 miles away. So we load up and go with a FULL and I mean FULL tanker load and get it over there when they call for one. Best part is getting the Free Stuff from this Plant every Now and then like Cookies and such.
Well, I’m just a little concerded, that you’re hauling truckloads of gear oil and acid to a cookie factory, but I guess that everybody has their own secret ingredients that make the cookies taste good.[C=:-)]
Besides how to unload and implode a rail car, how to unload and explode a rail car.
Concentrated sulfuric acid is nasty commodity. Tank trucks unloaded it using air pressure. Drivers loved the plant’s house air. It was higher volume and pressure than their PTO driven compressor could generate.
The problem was bursting the rupture disk required to prevent excessive pressure. One trick drivers knew was to insert a piece of a beer can in place of a rupture disk. This violation expedited unloading.
When unloading was completed, drivers would remove the beer can metal and replace it with a new rupture disk. When they returned to their terminal, or went through a D. O. T. road inspection, nobody was any the wiser.
Is this practice a known problem with rail cars?
Trust me the Boss has 2 Trailers Dedicated to this and they are Food Grade Tankers and after every load they haul they get a Through and I mean Through Washing with a Soap that is SO Strong that well lets just say the Drain lines at the wash rack have NEVER and I mean NEVER needed to be cleaned out since he got this one. The Acid tanks are a different trailer all together and the Gear oil 99% of the time is carried in a Van as they only ship it in 55 Gallon Drums.
Heck the Cookie plant wanted to use the Soap we use to clean out their Storage tanks one time and when they found out that we CUT IT 10/1 to clean a trailer they passed on it. For a Trailer Wash out they might use 2 Quarts of this stuff.
I sure hope you knew I was kidding. [:o)]
I know you where but with some people on here they might have taken what you said as the Truth. When people get bent out of shape over peoples jokes this place needs to lighten up.
I haul milk in a 6500 gallon smooth-bore tank, it can unload through a 3" hose, 2" thread (on the pump) in about 30 minutes, even with 30+ foot of “head” inside the storage tank. It can gravity unload (four foot drop, 3" hose) in about the same. Pump flow is about 200 gal/minute.
Brad
Thanks for that data, Brad. A 6" hose has 4 times the area, so about 4+ times the flow rate, hence 4+ times the volume in the same time: 4 x 6,500 = 26,000 gals. in 30 mins., pro-rate to about 35 mins. for 30,000 gals. Pretty good correlation for such an ‘off-the-cuff’ analysis.
And with a bigger hose, just get bigger (or multiple) pumps to handle larger flows.
- Paul North.
Paul,
Minor nitpick: For a given flow velocity in a conduit, the pressure drop should decrease with increasing diameter, so you “should” get more than 4X the flow rate with 4X the area. OTOH, there may be gotchas that increase the friction factor to make up for the reduction in L/D (that’s Length/diameter, not Lift/Drag for you aviation fans…).
Having said that, good job on the off-the-cuff analysis.
- Erik
Things like Head Pressure aka how Far you have to Pump it and how High your Pumping it come into Play Big Time. I have a Saltwater tank that holds about 300 Gallons in the Tank with a 5 FT head between where the Pump is mounted and the nozzle of the tank. Now I am only Pumping Water and I lost over 30% of what that pump could do in that little Distance however I am only Pumping 3200 GPH even at 5 Feet.