Oil isn't oil

A good-condition Bundy trumpet recently came across the bench with stuck valves and a request for a cleaning. That sounded simple enough, especially knowing that stuck valves usually just need to have their crud broken loose and they'll slip the rest of the way out. That wasn't the case here, though, as the valves refused to move at all. Removing the top and bottom caps revealed a thick green sludge throughout all three casings that was holding the valves tight. It was clear that someone had oiled this instrument with vegetable oil, perhaps under the mistaken belief that all oils are equal. I'd hate to be that guy's mechanic.

On facing this project, though, I thought it would be a good opportunity to share a couple pieces of research on why vegetable oil is unsuitable as a valve lubricant.

Mineral Oils and Organic Oils are fundamentally different.
If you use any regular (non-synthetic) valve oil, you'll see on the the side of the bottle that it contains petroleum distillates. A petroleum distillate is just a product made from refining crude oil, like kerosene, mineral spirits, motor oil, or in this case valve oil. Collectively these products are known as mineral oils, to differentiate them from organic oils like vegetable oil. To make things more confusing, mineral oil is also used to describe a specific type of petroleum distillate. It's the main ingredient in baby oil, is used as an animal laxative, and makes up the majority of commercial grade valve oils. 
Organic oils, on the other hand, are lipids produced by a diverse array of animals and plants. They share some basic chemical properties with mineral oils in that they contain a lot of hydrogen and carbon and repel water, but are derived in a completely different way from different sources.

Mineral Oils and Organic Oils have different physical properties
Mineral oils are thin at room temperature, with a relatively low surface tension between 22 and 28 dynes/cm. The average vegetable oil, on the other hand, has a surface tension of around 35 dynes/cm at room temperature. That added viscosity means that vegetable oils are too thick to fit in the small space between, say, a trumpet piston and its casing, which averages .025mm.

Organic Oils oxidize
Like the plants or animals from which they're derived, organic oils spoil after a time. It may take months or years, but vegetable oils will eventually go bad, and the high-humidity environment inside a brass instrument speeds up that process. Probably not a huge concern unless you plan to cook with it after you've used it to oil your trumpet, but worth mentioning.

Fortunately for me, Wayne Tanabe of Yamaha has a quick method for extracting the valves using a mouthpiece puller. I hope that posting these pictures won't infringe on his intellectual property, but the simple principle is that the valves don't need a huge amount of force to be pulled free, they just need a moderate amount of force, applied consistently. It does, however, require more force than your humble author could provide with my bare hands. A mouthpiece puller can provide it, though, thanks to that wildly popular simple machine, the screw.

The Bobcat made quick work of the valves. It really didn't take much pressure.

The oil got everwhere in the pistons, casings, and caps, and even oozed into the 1st and 2nd slides.

Having extracted all three valves, it was easy to see why they were so stuck. The buildup was thick and stubborn. Two cleanings in an ultrasonic only removed about half of the offending crud, and the rest had to be attacked with naphtha (a petroleum distillate!) and a large pile of cotton swabs.

If you want to know more about mineral oils, organic oils, or even synthetic oils, just visit your local library!

Just kidding, nobody goes to the library anymore. Go to Wikipedia. Or these other sites:

http://www.northerntails.com/images/What_are_Petroleum_Distillates.pdf

http://www.protectall.com/artpetdist.aspx

http://www.canitgobad.net/can-vegetable-oil-go-bad/