Air venturi compressor question

Hey dudes I recently bought a used air venturi electric compressor. It's the big one not the nomad. Anyway I want to replace the oil and water and do whatever maintenance I should do. My question is what oil works best? I have heard that there is the air venturi oil, synthetic motor oil, and standard motor oil. However I know from experience with industrial machinery that not all oils are created equal and often a different brand of oil works better than the brand of the machine. I think Royal purple was mentioned to me earlier. Also are the oil filters the same as the Ali express gold filters? I can save alot of doe if they are the same size. Also any tips or tricks would be great. I want this to last as long as possible. Thanks dudes. 
 
When dealing with "air compressors", it's Always Best to use "air compressor specific oils". 
I skip over all of the other options, and exclusively go with Royal Purple. It's amazing stuff, and I Highly Recommend it. 

https://www.royalpurple.com/product/synfilm-recip-100-reciprocating-air-compressor-oil/

I grab mine at whatever 'NeverAnyPartsAvailable' that I'm closest to - Usually around $20 bucks for the quart size. 
Some people cry about the price, but, I'll spend a bit extra to have a better and longer running compressor as time goes on.
Also, I've been using it exclusively for almost 20 years when it comes to home / industrial / shop compressors.

Anyways.. Here's an interesting one for ya..
The last time I had to do an oil change on my [now over 1 year old] YH compressor, I drained the oil into a paper towel & coffee strainer, 
inspected it, and the used oil still looked perfectly fine.. No worrisome debris/flakes, so I continue on..
Then get sidetracked because, well, if I see anything shiny, my attention span is shot..

Get things buttoned back up [or so I thought] and fired up the compressor..

I had to completely fill a 97 cu/ft Great White carbon fiber tank.. from 0 to 300 bar, AND, top off my other 88 cu/ft tank from 220-300 bar.

The comp ran, and ran, and ran.. I double checked the tank PSI and checked for any air-leaks, 
and That's When I Remembered - - - I Had Completely Forgotten To Refill The Comp With Oil.

D-E-R-P ! ! ! ! 

Talk about a rookie-mistake! And from someone who's been a mechanic for over 20 years.. 
[And I'm admitting this publicly to show 1 how good the Royal Purple is and 2 to show that everyone makes mistakes. At least once per lifetime. lol ]

Back to the ramble..

I shut off the comp, let the water continue to circulate to help completely cool things down. [Which - Temps were Still Not Excessively High Anyways]
Then with a light and scope, I inspected the inside of the comp's block, and nothing looked out of the ordinary.. I was actually a bit amazed..
I did a quick oil-fill/drain/flush, and inspected that oil for any bits, debris, filings, etc. Nada. Everything looked good..

This Time - I Remembered To Fill The Comp With Oil. hahaha

I then proceeded to run it [obviously periodically stopping for intermittent cool-downs] for long enough to Completely Fill the 1 tank and top off the other! 

Zero Issues! Now, this could be happen chance.. It's not *luck* because I only have 'bad-luck'. 
In my professional opinion, the Royal Purple definitely played a part in keeping the comp's internals amazingly lubricated, etc. while it was running.. 

At this point, I had a few other oil that I was intending on trying out, but, not anymore.. Sticking to the RP forever now. haha

Alright, I'm done..

[/Mini-Novel]

🤣👍 

Sam -
 
I feel like there is more oil mixed with water than I was expecting when bleeding the air out. Is this normal?

When bleeding out moisture/pressure, yeah, with almost all OEM setups, it's pretty much 'normal' to expect to see 
somewhat of an oily-watery mix to some extent.. This is why it's always a great idea to run an external / in-line 'moisture / oil separator' 
or moisture/oil-filtration system. The cotton filtered versions will work in a pinch, but, the best is to go with something using desiccant.. 

The issue can be caused by gaskets/sealing, heat, cooling, condensation, etc. 
Pretty much not 100% avoidable, but, we can definitely limit the amount for sure.