discussion Preventing rust in compressor tank

[HAWKERHUNTER]

Morning chaps
I am just awaiting the arrival of a new compressor with tank. I have been reading that the steel tank can be prone to rusting internally. I am aware that the general advice is to drain the tank after each use but this compressor will live in my workshop which most of you will know is in a stand a lone garage and can get very damp at times. Is there any other precautionary steps I can take to prevent rusting in the tank. Thanks.

 

[PaulTRose]

It will take a lot of use of along time to get rust in the tank

How you going to know anyway? Its a sealed tank

Ive burnt out motors and electrics long before corrosion is a worry

 

[HAWKERHUNTER]

How you going to know anyway? Its a sealed tank

You will know when you start getting rust coloured water in the trap. I would imagine that some more expensive models may be fitted with a stainless steel tank but this is not high end so I am assuming it will have a steel tank.

 

[Mr Bowcat]

I have both an airbrush compressor and a 50l workshop compressor, and take the time to drain the tanks at the end of each use. Although unlikely, if the tank gives up from rust when fully pressurised it's going to be a bad day. Better safe than sorry.

 

[Jim R]

I always release the tank pressure with the drain valve at the bottom of the tank and then leave the drain off until I want to use it again.

 

[Andy T]

I do as Jim does, draining after each session then leaving the drain open to allow any remaining humidity to escape.

The number of times I've switched it on and forgot to close the drain first...

 

[Tim Marlow]

For those that don’t know……

1. Compressor tanks are usually made from mild steel.
2. Mild steel, in conjunction with moisture and oxygen, will rust.
3. All air holds moisture.
4. When you compress air it warms up, and will then hold more moisture.
5. When you draw off compressed air the resultant pressure drop cools the air, making it less able to hold moisture. The excess moisture then coagulates as condensation. This happens in both the tank and the delivery tube during normal use. As a rough measure, my tankless compressor generates about 20mL of water in a decent session. As my compressor is tankless this is captured in the moisture trap on the air feed to the airbrush. It’s worse on damp days.
6. Condensation formed in the compressor tank will congregate at the bottom of the tank because the air outlet is at the top. Unless you drain this off it will cause rusting in your compressor tank. The rust will be localised at the bottom of the tank and over time will significantly weaken that area, possibly with explosive results during use.
7. Draining the tank via the drain valve at the end of the session is therefore a very good idea.

Slightly tongue in cheek, but I’d rather teach you all to suck eggs than hear someone has had a nasty accident…..please don’t take offence.

 

[John Race]

Very true Tim, ask any one who was in the Army what that had to do at night on their vehicle, drain the air. The amount of moisture that came out was amazing.

 

[pjgtech]

One of my other hobbies is airgun shooting, and as well as Springers I have PCP's (Pre Charged Pneumatic) guns which use high pressure air, eg: anything from 160 bar to 300 bar, and I use a compressor (user rated for 300bar, safety tested to 450 bar!). One of the things airgun users worry about is corrosion inside the gun or its pressurised cylinder, (not inside the compressor) so we have filters on the compressors to stop moisture getting into the gun.
The compressor obviously takes air from its surroundings, (atmosphere) which has water vapour in it, unless you have very, very low humidity.
When air is compressed the water vapour is squeezed out of it, hence the liquid water droplets.
When I fill my guns there is always a little (tiny) bit of water at the end that comes out of the compressor, after turning it off and releasing the pressure relief valve.
So I suppose if you are are really worried about it could you fit some sort of filter on the air intake side of the compressor? or as above, just make sure you drain it whenever you can...