Compressor tank needs cleaning?

I picked up a really nice Peerless 40L compressor recently, just for occasional small tool uses. It's only a couple of years old and has around 1000 hrs on it. I opened up the pump to service it but all the seals and internals are looking mint.
But there is a little bit of cruddy brown fluid in the tank. Even after several bleeds from maximum pressure there's still a tiny bit. I opened the end plugs on the tank to check it out.

Attachment 535591 Attachment 535592 Attachment 535593

The colour is wrong for rust, I'm pretty sure its just oil/water mix.
Thoughts?
is it enough that I should try and clear it, or is this just normal?

I'd say it was normal. Air contains CO and CO2, NOx and SOx. These dissolve in the water that condenses out from the compressed that cools inside the tank. As they dissolve they form weak acids which over time cause corrosion. About all you can do is make sure you regularly vent the water inside the tank. I have mine set up with an auto tank venting solenoid connected after the vent tap and leave the vent tap open.

I've tried the $40-$50 auto tank venting valves that are available on ebay.
1/2" Automatic Electronic Timed Air Compressor Auto Drain Valve AC 220V | eBay
I set mine up so it get its power from the Pressure switch only while the compressor is switched on. Ideally you want to bleed the water some time after the last compression cycle so that the water vapour it has time to cool down and condense. If you draw power from the pressure switch only when the motor is running it's unlikely that the vent valve cycle will coincide with the compressor motor cycle so it never vents. I set mine up so they are powered as long as the compressor is switched on at the mains - ie independent of whether the motor is running. They typical bleed 0.5 - 10 s of air every 0.5-45 min so if you forget to turn off the mains switch the entire tank will eventually be vented to air. You can of course just provide power directly to these valves but then you need to remember to switch them on off.


Another problem with these auto vent valves is they seem to fail after 2-3 years and I have gone thru 3 of them. Since then I've used a HD 240V solenoid powered independently and switched on/off by a small Arduino controller programmed that vents in the same manner. I installed the first of these early in 2019 and it just failed, so based on a grand total of one failure, it looks like I get 5 years from them.
AC 220V DC 12V-24V Normal Closed Electric Solenoid Valve Water Air Brass N/C AU | eBay

You could hook up one of these and just manually switch these every now and then.

Thanks for the feedback BobL :)
There's a really good Jorc auto drain that came on it, but I removed that because it wasnt having any effect, and I planned to just do a manual bleed every now and then instead. It was connected to a port on top of the tank (here's the original setup) that had a drain hose running down to the bottom. But as you can see in these pics it doesnt go down far enough.
It never occurred to me to fit the auto drain to the underside bleed port instead :doh: I might give that a go instead.
Looking at whats still left in the tank in these pics, do you reckon I should try to flush it out before I seal the tank back up?

I bought a 1976 Ford Louisville truck in 1980 on which the air tanks were equipped with automatic drain vents. Working in the high humidity of the Pilbara they were not draining the condensation from the tanks efficiently. I ditched them and replaced them with manual valves which I would open and leave open at the end of the day. In the morning I would fire the engine up then close the valves after a minute or so, over the subsequent twenty years of running that truck I never had any problems with condensation getting further down the lines.
My shed compressor I treat the same, I open the drain valve at the end of the day and close it next time I go to use it.

Cheers,
Geoff.

Quote:

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Originally Posted by Boringgeoff

I bought a 1976 Ford Louisville truck in 1980 on which the air tanks were equipped with automatic drain vents. Working in the high humidity of the Pilbara they were not draining the condensation from the tanks efficiently. I ditched them and replaced them with manual valves which I would open and leave open at the end of the day. In the morning I would fire the engine up then close the valves after a minute or so, over the subsequent twenty years of running that truck I never had any problems with condensation getting further down the lines.
My shed compressor I treat the same, I open the drain valve at the end of the day and close it next time I go to use it.

Cheers,
Geoff.

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Sounds like a good way to run it. Did you ever get a look inside the tanks or the lines, see how they handled it?

When you release the parking brake air is fed down the lines to the four rear brake boosters to hold them in the off position, when you put your foot on the brake pedal air goes down another six lines to the four rear and two front brakes to engage them.
From memory, bearing in mind this was over forty years ago, I disconnected all the lines at their destinations and operated the park and foot brakes to blow whatever moisture there was out of the lines.
I can't remember trying to look inside the tanks, but as the truck was only a bit over four years old at the time, I probably assumed they were not corroded.

Cheers,
Geoff.