Killer compressors
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
For most people never! Let alone drain water. Most compressors also have very thin tank walls in the light duty class. I have also seen plenty of pressure ratings exceeded and tank safety releases replaced with pipe plugs. I have been doing pressure vessel inspections for decades in the industrial sector and there is no lack of surprises. I have seen tanks so rusted they still passed a hydro test but fail a visual. On the other hand I have seen clean tanks pass visual but fail hydro at just 10% over rating. The amount of stored energy is unbelievable in a pressure vessel and its not often you walk away from a failure unharmed.
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Fleet Owner
Joined: Apr 2012
Posts: 27,307
Likes: 549
From: Spanaway
The one place we see a increased risk in onboard compressors and storage tanks on our trucks.
I would bet that those little tanks get ignored more than the larger units that sit in shops or under
a bench out in the garage. That is not even taking into account the really cheap tanks from China.
I would bet that those little tanks get ignored more than the larger units that sit in shops or under
a bench out in the garage. That is not even taking into account the really cheap tanks from China.
Hotshot
Joined: Dec 2014
Posts: 17,823
Likes: 3,101
From: Jersey Shore
I've been looking at replacing mine for the last few months. I replaced one at the test facility that was made by our company when they were making them. The unit was from the '40s but massively heavy due to the tank wall. The electric motor was crazy built too.
I've drained mine routinely but always amazed at how much water is in the tank. I'll have to go back in and record the video from a borescope inspection.
I've drained mine routinely but always amazed at how much water is in the tank. I'll have to go back in and record the video from a borescope inspection.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
The next issue on light duty compressors is self induced. These compressors use very cheap 3450rpm motors and often the pumps are direct drive or sheaved to run the pump above 1800 rpm. This creates massive heat and the water turns to vapor and condenses in the tank quickly. This is why you see very little moisture on industrial compressors in the tank especially when pump speed is below 800rpm and often at 680rpm. These pumps don't super heat the air like the low displacement high rpm pumps. My personal shop compressor is a Quincy 375 Pump that runs 550rpm and moisture in the tank is never a issue. I do have a auto drain set for every 60 min which helps but the pump never gets very hot even on the second stage.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
I use auto drains on tanks because (as a welder) I see PLENTY of chitty welds on almost all tanks I look at.
The non-destructive tests they use at the factory only work when new. ALL tanks have problems with water / moisture over time, then you get the destructive tests (pictured above). Tanks are like concrete over time (99.9999% of it cracks).
The non-destructive tests they use at the factory only work when new. ALL tanks have problems with water / moisture over time, then you get the destructive tests (pictured above). Tanks are like concrete over time (99.9999% of it cracks).
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Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
Thankfully I'm never hugging my 60 gallon compressor tank. And it gets drained of water every day I'm done using it. On the truck OBA tank it is drained every time I service the truck and barely a half of a teaspoon of water comes out. I'd like to think most others do the same. Maybe not.
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Fleet Owner
Joined: Nov 2003
Posts: 27,872
Likes: 3,592
Thankfully I'm never hugging my 60 gallon compressor tank. And it gets drained of water every day I'm done using it. On the truck OBA tank it is drained every time I service the truck and barely a half of a teaspoon of water comes out. I'd like to think most others do the same. Maybe not.
That said, my portable tank I carry in the truck is stainless.
Hotshot
Joined: Dec 2014
Posts: 17,823
Likes: 3,101
From: Jersey Shore
I do the same, drained at the end of use and depressurized. I shut off the power, open the drain, and let it all bleed down that way. I replaced the original valve with a 1/4 turn Swageloc stainless, extended it to the side. There is no reason to leave a potential bomb for the wife or firefighters.
It's interesting in Sean's added video that it blew down the seam.
It's interesting in Sean's added video that it blew down the seam.
Fleet Mechanic
Joined: Sep 2006
Posts: 1,491
Likes: 295
From: Fresno, CA
Good example is micro-waving a hot-dog. Always splits down the middle, doesn't blow the end off.
Hotshot
Joined: Dec 2014
Posts: 17,823
Likes: 3,101
From: Jersey Shore
I was just pointing it out.
I'll add IMO weld seams are usually the weak point, not the weld itself, but the material next to the weld gets annealed and the crystalline structure is altered. Same as doing the stupid move of hardening the base material for a valve seat.
Depending on the filler and base metal, also the potential for creating a galvanic cell (accelerated corrosion) at that location due to the dissimilar metals, as well as any oxygen concentration gradients that may have been created, or any hydrides or oxides which may have formed during the process. Not what you want in an air compressor tank, and why the good ones are more expensive. Way farther down the rabbit hole then I was intending for the comment; geez it's just a diesel forum.....
I'll add IMO weld seams are usually the weak point, not the weld itself, but the material next to the weld gets annealed and the crystalline structure is altered. Same as doing the stupid move of hardening the base material for a valve seat.
Depending on the filler and base metal, also the potential for creating a galvanic cell (accelerated corrosion) at that location due to the dissimilar metals, as well as any oxygen concentration gradients that may have been created, or any hydrides or oxides which may have formed during the process. Not what you want in an air compressor tank, and why the good ones are more expensive. Way farther down the rabbit hole then I was intending for the comment; geez it's just a diesel forum.....
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Fleet Owner
Joined: Apr 2012
Posts: 27,307
Likes: 549
From: Spanaway
Jack your forgetting that it's not just a Diesel Forum but a Diesel Truck Forum.
There are quite a few people out there that put a compressor in the trucks.
There are some out there that have put the small cheap tanks in that run the risk
of a tank failure.
There are quite a few people out there that put a compressor in the trucks.
There are some out there that have put the small cheap tanks in that run the risk
of a tank failure.