Hello,
Is there any way to figure out the capacity of a portable air tank?
I was given a nice but used "Speedaire" (made by Dayton) portable air tank. It looks to me like a 6 or 7 gallon tank (9.5" Dia. X 19" approximate length). Unfortunately, there is no rating plate which states the maximum capacity. The gauge goes go up to 125 PSIG before it reads "DANGER", however I do know that it is not the original gauge.
I looked up the model # (4Z492) in my Grainger catalog, but it must be discontinued or something.
Anyone familiar with these tanks? Thank you in advance for any help you can provide.

 

Kenny,

Rounding down, for wall thickness and rounded ends:

( ( Diameter x length x Pi ) / cu-inches-per-cu-ft ) * gallons-per-cu-ft

( ( 9" x 18" x 3.14159 ) / 1728 ) * 7.5 = 2.2 gallons

But, I was never very good at math...

[i][font color=red]-Mark[i]

[font color=green]'85 F250 4WD 460
'85 Yamaha XJ700 Maxim
'83 Mustang convertible up on blocks

[font color=blue][i]"If a man speaks and no woman hears him, is he still wrong?"[i]

 

I have an air tank whith about the same dimensions. It is a 7 gallon tank. The guage is probably the orig. and trust it. Don't go over 125 in that tank can get dangerous. If you do there should be a relief valve but personaly I don't trust them.

 

Mark-

Your rounding factors were probably pretty good assumptions so I will use the same figures. You forgot one thing; Area =(pi) x Radius(squared). You had the formula for circumference. Keep working on the math homework.

So we can calculate the area of the end of the tank and take that times the length of the tank to get the number of cubic inches in the tank. Then we can divide by the number of cubic inches in a gallon(231).

Since 9" in diameter is a 4.5" radius.

3.1416 x 4.5 x 4.5 x 18 = 1,145 cubic inches (neglect the decimals)

1,145 / 231 = 4.9 gallons

Since we were "guesstimating" on dimensions, and the original designer was probably shooting for a round figure...
Call it a 5 gallon tank!

There should be a pressure relief valve, if there is not, you can get them most anywhere. Get the type with a ring on the end so you can give it a pull every so often when pressurized to make sure it is not all corroded up. It should release air when you help the spring by pulling on it.

Most air tanks are designed and constructed for a certain safety factor to allow for abuse and corrosion. A portable air tank for normal service work should be rated for use at 125psi.

Pull the fittings out of the tank if you can and clean it out. A portable tank needs draining just like a regular air tank to keep moisture from rusting out the tank bottom. You just have to drain it thru the hose...

-And yes, you are still wrong by definition. It does not matter whether a woman is around.

 

Thank you for the very quick responses!
Don't worry, I definately would never go over 125 PSI! In fact, my biggest concern was if the tank would explode at 70, 80, or 90 PSI if the gauge was meant for a larger capacity tank. I also never realized that the pressure release valve with the ring on it was an overfilling safety feature. I had thought it was only to empty the tank. The tank has been emptied and cleaned out, and I'm now ready to use it with confidence. You guys are the best! I learned a lot. Thanks again!

 

Have you checked to see if speedaire might have a website or check with a compressor shop if there is one near you i think speedaire is still in business.I have a compressor shop less than a mile from me if you come up dry on your end maybe i can help.





Wiz

 

Kenny-

One other thing that you can do to ease your mind is get the tank pressure tested. This process uses a liquid in the tank to avoid the explosive effects of air if something gives. It also costs $$$ and kind of kills the "free" tank. If the tank is in good shape externally and you didn't get a whole lot of crud out of it you should have no problems. Rust will usually show up as pinhole leaks in the tank unless a seam is involved. The welded seam should not be on the bottom of that type of tank. A little detergent type motor oil poured into the tank will help prevent corrosion by keeping the water in suspension and coat the tank.

More topics to check on air tips:

Get the Water Out!
Air Tool Lubrication
Check the warning on PVC pipe with compressed air [DON'T]!!! Kenny should be familiar with this one.

There is also a thread on choosing a compressor with lots of info.

 

I work in the LP Gas Industry and while I will not swear to it most ASME Pressure vessels are built to a 4 to 1 "saftey" margin. Meaning if the "working" pressure is 250psi then the "burst" pressure would be 1000psi. By all means make sure you have a new relief valve in it and keep it drained.

Regards
Gasman

 

Update.....
First, I want to say thank you to all who replied! I learned some very valuable info from all of you.
I was able to contact Grainger via. e-mail, and they looked up my obsolete model number. They told me what I have is a 6 Gal. tank, and they gave me a cross reference (new) model number for ordering replacement parts in the future. Thanks again, you guys are the best!

 

Check your dimensions and run them thru the formula. Unless your dimensions are wrong they may be rating that tank like the new phony Horsepower ratings :-)

The steel in the tank is at least 1/8" thick but should be around 3/16" thick. You can find the diameter of the tank by measuring the circumference and dividing by 3.1416. Reduce the diameter by the thickness of the tank walls x2 (3/8"?) then use that for the inside diameter of the tank.

Of course you could always weigh the tank empty w/o fittings and figure the surface area, then back figure the steel thickness... But I doub't if you want to go that far. -hehe But if you do, I can run you thru the calculations.