Stay from those old compressor---

[superwelder]

ya no ****. give it a couple weeks and your see a thread titled "why did my compressor blow up".

also, i was looking through this thread and saw that all a hydro test is is a pressure test with water. i don't understand what that tells you, you will see that it will hold pressure but in no way tells you what condition the tank is in on the inside. thats what i was worried about.

[anickode]

A hydro test is pressurizing the tank with water, while it's submerged in a tank of water. The large tank has a very precise measuring device on it, allowing to read the variance in displacement between the unpressurized and pressurized states of the tank.

They measure initial depressurized volume, stretch volume under pressure, and depressurized volume again, to tell whether the tank is fully returning to spec'd dimensions each cycle.

[DSW]

i don't understand what that tells you, you will see that it will hold pressure but in no way tells you what condition the tank is in on the inside. thats what i was worried about.

Compressed gas cylinders are also hydro tested. I'm most familiar with those, so I'll use that as an example, but compressor tanks are tested in a similar manner.

Test pressure varies based on cylinder type and material. For example DOT 3AA 2015 steel cylinders are hydro tested to 5/3rd their working pressure and held at that pressure for a given length of time. If they are plus rated, they go up an additional 10%. So a 2015 would have been taken up to 3360 psi, and if plus tested, it would have checked out at 3700 roughly. As mentioned they check what the displacement is at the start and compare it to the displacement at the end. a cylinder or tank with heavy pitting and rust will usually fail in some way at the elevated pressure. Either it will deform and not return to it's original dimensions, or it will "burst" and the pressure will drop prior to the test ending.

A rusty air tank would most likely "burst" when tested if the walls were thin from rust. Because the tank is filled with water, not air, you get a leak, not a bang. So indirectly you would get an idea what the interior surface was like. You could also get the walls tested by ultra sound that will pick up differences in wall thickness, but that will not tell you what a "safe" working pressure is. All it will tell you is that the wall is a different thickness there. You also have to cover ever inch of the tank with the ultra sound to know for sure what the walls are like. Hydro tests everything at once, and the weakest point, no matter where it is will let go first.


Note that generally with compressed gas cylinders, the "safety" or burst disk is usually set at the hydro test pressure for the cylinder or just below it. These disks are guaranteed to let go at or below the listed pressure, so chances that a cylinder would ever exceed the pressure it's been proven to hold is very low. In theory the same general idea applies to air tanks. The blow off should be set at a "safe" pressure, and should be tested regularly to make sure it still functions. Should the compressor not shut down, the safety should let go and vent the cylinder before something else lets go.

Unfortunately air tanks are seldom maintained well. Safeties often get frozen and will not open and because no one tests them you never know the problem exists.Tanks also aren't drained and develop rust and weak spots. These weaknesses aren't caught because people seldom bother to hydro test the tanks. Start adding all these factors up and that's when bad things can happen.

[superwelder]

well i do make sure the safety works because i use it to bleed the air out. as for the water/rust, i'm guilty of that, i do drain it but not as often as i should. about how much should i expect to pay for a hydro test and how do i find a place that does it? would it be cheaper just to get another compressor?

[ThorsHammer]

if you go back on this thread someone shows a tester that can do the preasurizing, but doesn't measure the deformation and return. You'd have to figure out something for that if you wanted to do it yourself. If you plan to maintain the compressor/tank on a regular basis this would be what I would do.

[superwelder]

ya i saw that setup, thats why i asked. i'm thinking about getting a bigger compressor anyway so i might just keep this on the side for when i need a portable one.

how can i completely dry the inside of it?

[ThorsHammer]

how can i completely dry the inside of it?

cut it open and make a BBQ out of it.

[superwelder]

already have a 120 gal. waiting for that to happen to it.

[fredschrom]

The head on that POS won't last six months, the tank will outlast it. Those are some pretty crappy welds patching that propane tank, its Somolian pressure rated.

[woi2ld]

a big Wayne Dresser explodes in a tire shop. Saw this today, remembered this thread, thought i would share...

[Rora]

If you think that's bad, check out hydraulic accumulator which can have up to 10,000 psi in a unit about the size of a basketball. One unfortunate fellow tried to work on one without depressurizing it and it blew through 2 internal walls then another and ended up outside. I don't recall if he lived or not...

[weldbead]

What do we think? Stuck pressure switch and inaccurate gauge?
I wonder why the relief didn't blow off?

Doesn't look like a rust-weakened reservoir failure, just looks like overpressure.

Good Luck

i aint sayin all my tanks get blown out on a regular basis..i bet that one blew on the bottom cause it was weaker there from whatever condensate it held all its life..

[blackbart]

I also work on a volunteer fire dept. In 30 years I have seen two tank explosions, one took the guys legs off. I don't think there is a hydro test date interval on air tanks, but started noticing "take out of service by...."stickers on new compressors.

[blackbart]

Of course I realize my last post totally contradicts my other post on how much fun it is to vent a 250 gallon propane tank with a lit rag........sometimes making memories overcomes my common sense.

[Charleyhorse]

if you don't know their history. The pics will tell more than I can type since I only (fortunately) have the use of my dominant right hand. Our son was given an old craftsman 3 hp 220 v. we got him a brad nailer for christmas, so he bought an air hose to try it out. i was hunkered down beside it watching the gauges. when it hit 130 psi i pulled out on the pressure relief to make sure it worked and it did. when it hit 150 psi i was about to lose my nerve and shut it down. then the tank blew, luckily for me, out the bottom...............

Well, I was just looking in the tools section in Craigslist and here is the very same compressor. Would you like to try your luck on one of these a second time? This one seems to be ready to blow. The ad says it has a small leak on the bottom of the tank that can be fixed by a bit of welding. It's all yours for the hot price of just a hundred dollars:

http://knoxville.craigslist.org/tls/4351600999.html

Sears Air Compressor
This is an older compressor but works very well. Has a large air tank with a small leak on the bottom. Could easily be repaired by a welder, but the leak is so slow it doesn't affect the use of the compressor. Will hold pressure for 30 min or more no problem. Has had the compressor portion replaced about 5 years ago. Runs on 240V. I have replaced this with a smaller 120V compressor since the places I could plug it in at 240V in my house were limited.

[DSW]

"for sale, live grenade, some parts missing ( pin)...."

[socoj2]

If you think that's bad, check out hydraulic accumulator which can have up to 10,000 psi in a unit about the size of a basketball. One unfortunate fellow tried to work on one without depressurizing it and it blew through 2 internal walls then another and ended up outside. I don't recall if he lived or not...

Doesnt sound right. Since its fluid not compressed Air. Ie See hydraulic vs Compressed air explosion

[ltvtom]

How Accumulators Work

http://www.epa.gov/otaq/technology/r...ccumulator.htm

[mla2ofus]

Doesnt sound right. Since its fluid not compressed Air. Ie See hydraulic vs Compressed air explosion

A hyd accumulator usually has a nitrogen filled bladder in it designed to absorb shock loads to the system. It also can have other uses in a hyd system.
Mike

[tanglediver]

"for sale, live grenade, some parts missing ( pin)...."

Ha! Got that right!

[Poppa Steve]

Late to this thread, Wow! I'm glad things weren't worse than they are.

[woi2ld]

Our 120 gallon ingersoll rand came apart worse than this before it landed in the shop parking lot. I think mexico and other countries are not as strict as us with their pressure vessels. I thought maybe the pump and motor was good untill i notice the flywheel was probly broken off in this video. Lol, and i think he's saying the pressure switch didnt work, or maybe "this pin is still in the grenade what happened"

[docwelder]

they are very lucky to be around to tell what happened.

[gnm109]

I'm sorry to hear about the OP's injuries. I hope for a good recovery.

I just scrapped an old compressor that I bought on Craigslist last year. I got about 6 months use out of it. I only used it for an airbrush in an upstairs workshop. It developed leaks in the underside so out it went. You really can't be welding on those old tanks. There's no metal left to weld to.

My other compressor is a USA built 80 gallon vertical with a real 5 hp motor. I drain it all of the time and it's been good for more than ten years now.

When I got it, the high pressure was set to shut off at 175 psi. I immediately turned that down to 125 psi since I never use my air tools at more than 90 psi. t starts at 100 psi and shuts off at 125 and that works OK for me.

[pepi]

Here is a suggestion, I use this on my compressor, as auto drains go this is a winner, no timers to set, no need for electric service, and the price is great. The range I have seen for the Moisture Minder is 80 - 130 $$ the link below is the lowest price I found, of course I quit looking after I installed mine.

http://www.rite-products.com/Moistur..._p_800394.html

See the line T ed, goes down to the top of the valve, that is the trigger for the drain cycle



Because the tank always has pressure, allows the valve to be mounted above the lowest point. The air is always forcing the water out of the tank. Gravity has no effect if the tank is at pressure.


Tsunami Moisture Minder, Automatic Drain Valve

Automatic; operates each time your compressor cycles
Requires NO ELECTRICITY
Stainless Steel Reservoir
Seals made of Teflon and Viton
Rated to 300 PSI
Valve Creates NO LOSS in air system
Manufactured in the USA

The Tsunami Moisture Minder is a universal solution for your air compressor auto-drain needs. Working with the cycling of the air compressor, this drain valve drains your air tank each time the compressor turns on and off.

Great insurance, I have run this thing for a year now, check the drain manually and it is always dry