Leave pressure in my compressor tank, or drain it every time I shut it off?

[wayback machine]

I leave mine full, with a ball valve to shut off the whole system.
When I'm not using it, I shut the compressor off - With the tank full, and the power off, there's still pressure a week or more later.
If there's 125psi in the tank when I shut it, there will still be at least 90-100 psi left.
I've learned not to leave the system open to any quick connects, with or without tools attached, if I'm not using it - The tank valve is the key.

 

[Winegrower]

I added an auto drain, so every time the compressor starts there's 4 seconds of drain. I've never found any water at the in-line sumps. I also added a remote low voltage shutoff switch and when I remember I turn off the compressor overnight. It's about at half the next morning.

 

[PNW_Guy]

I either close the valve or throw the power when I leave. I always turn off the power if I'm going to be away for any length of time.

 

[B2]

My quick disconnects bleed down anyway. However, what about safety. If a line breaks or a child is fooling around? On the other hand a couple of hundred PSI in a steel shop tank probably does not harm the tank. Water in the tank is the bigger issue. My father-in-law had a compressor and during his latter years I don't think he could work in the shop much as he had mobility issues, so the tank seldom got drained. It developed a rust hole!

By the way, I Scuba dive .. a little. In this case, the filled pressure is ~3000psi and the air is suppose to be dry as water is not suppose to get into the regulator and gauges. I have a couple of Al 80 cubic foot (80 at STP when filled to 3000psi) tanks. They have to be inspected via pressure tested every 5 years to ensure there are safe to use. I am not for sure, but I think the test takes them up to 5000psi or so. I think constant fill pressure in the tanks can increase the likely hood of cracks forming. One can also remove the valve and inspect the tanks visually or inductively for cracks, but the 5 year pressure testing is required before it can be refilled. On the other hand one never wants to completely empty a Scuba diving tank as this would either indicate it was emptied under water during a dive and could indicate that there was no back pressure on the value .... to prevent water from getting inside. Dive shops should not fill a tank that has been completely emptied without first inspecting the insides. Getting water, especially salt water, into the regulators means that the regulator has to be rebuilt! There is a rule, return from the dive while there is still a few hundred pounds of pressure left in the tank .... 500psi, but even 100psi will do.


Dave L.

 

[brino]

When I shut mine off, the system bleeds down in a couple of hours. The quick connects are usually the culprits.

My quick disconnects bleed down anyway.

The best upgrade I have made to my air system was following John's (@pontiac428) advice here:
https://www.hobby-machinist.com/threads/what-did-you-buy-today.55645/post-1026530

Just replacing all my quick connects with the Milton red ones made a world of difference!
The system now takes days to leak down instead of hours.
I can get them on Amazon for about a dollar a piece.
Sure is surprising how many of them there are in my modest little shop.

Brian

 

[epanzella]

My 60 gal compressor tank is always pressurized. I put a ball valve right on the output of the tank and close that when I'm not using air. This prevents leak down and cycling 100%. My tank is vertical so draining it required getting on my knees and reaching under the tank to open the petcock. I extended the drain out the front with a ball valve that I can open and close with my foot. Now I drain the tank muck more frequently.

 

[PNW_Guy]

My quick disconnects bleed down anyway. However, what about safety. If a line breaks or a child is fooling around?

If there's an unsupervised child in my shop, something has gone very, very wrong. There's more than 1,000 ways to die in there - and absolutely no reasonable way to child proof it.

I have a ball valve on the outlet, so a line shouldn't break but if it does nothing happens after the line pressure bleeds off.

 

[verbotenwhisky]

Mine does 22CFM at 120PSI and 30CFM at 90 PSI with a 1 gallon receiver; so, I have no opinion...

 

[alloy]

I have a ball shut off valve and thankfully it doesn't leak at all. I do howerer have to replace the automatic drain every once in awhile. It sticks open and can't do anything but replace it.

I had to look at my compressor, it is 24cfm @175psi. It pumps up fast, but thats a lot of motor to be spinning over for no reason.

So I guess I'll keep leaving Jeannie in the bottle

 

[RaisedByWolves]

To the folks advocating bleed down, why does it ever make sense to bleed your compressor down?

GsT

I’ve only read this far in the thread, but food for thought.

It takes oxygen to allow oxidation to form and eat away at the walls of your tank.

A non pressurized tank will only have so much oxygen in it available to allow oxidation, while a pressurized tank will have ~10 times as much air, hence oxygen in it.

With this in mind you can see how much more potential for oxidation on a pressurized tank long term vs one that is blown down.

Will it ever matter? I don’t know, but that is the long/short of it, and you usually don’t find good tanks that need a new pump, it’s usually the other way round.

I see wear and tear on the pump as being negligible and I don’t worry bout the lectric as I get it delivered fresh daily.