Any case that is waterproof should have a purge valve. It lets air flow freely in & out of the case, but prevents water & dust from entering. A purge valve is important on watertight cases because the atmospheric pressure at different altitudes will cause the pressure inside of the case to be different than the outside. This causes a vacuum & will prevent the case from opening. For example take a plunger and push it down on smooth tile or glass. It will be next to impossible to remove the plunger because you’ve created a vacuum. In essence the atmospheric pressure within the plunger is different than the outside.
This concept works the same with cases. In a real life example if you travel from Florida (at 0 ft above sea level) to Iceland (6,920 ft) above sea level your case will most likely break or significantly disfigure without a purge valve.
There are two main types of purge valves. Automatic purge valves found on most cases such as Pelican or SKB & manual purge valves found on lesser known brands. If the purge valve is automatic you don’t have to do anything to make it work as it functions automatically as you travel. Manual purge valves on the other hand usually require you to push a button to release the pressure. Be careful though! If your case has a manual purge valve it could already be disfigured or damaged by the time you reach your destination which defeats the purpose of a purge valve altogether.
Finally remember… If someone says a case which has an automatic purge valve (like Pelican or SKB) is airtight they are wrong. The case is not airtight, but rather watertight because as you just learned an airtight purge valve would be pointless!
So you need a waterproof case, but want to avoid spending a ton of money on a name brand like Pelican? Well you’re in luck. Nowadays there are so many case manufacturers competing for your business you can still get “Pelican Case” quality at a much lower price.
Here is a top 5 list of waterproof (military spec) case companies from most expensive to least expensive. As a professional I would be happy using any one of these for my shipping needs.
Short answer with all things considered we choose:SKB Cases
Long Answer to understand the short answer:
Currently the top 3 case manufacturers are Pelican, Storm & SKB. Well… Kind of. Lets clarify a few things first by going back in time a few years.
Pelican was the innovator of waterproof cases. They were the first to market & by far the largest case company in the word. Most industries recognize the Pelican brand & for good reason. Their cases are some of the best money can buy. Storm cases on the other hand (once owned by a company called Hardigg) was #2 & SKB was still an unknown brand. As time past & competition grew more fierce between Pelican & Hardigg a change occurred. Pelican bought Hardigg & therefore inherited their Storm cases. They chose to keep the Storm line & sell them as “Pelican Storm Cases.” That’s why Storm cases are priced almost exactly the same as Pelican cases.
After the Hardigg acquisition by Pelican they raised prices on both the Storm line & Pelican line simply because there was no competition. They owned the market. By raising prices however they opened an opportunity for smaller waterproof case companies to enter the market. That’s when SKB started to lead the pack. They created cases which had the same features & lifetime warranty as Pelican yet they offered the cases at a more affordable price. Although the SKB case brand is not as recognized as Pelican the quality is still on par. In essence by purchasing SKB you’re buying quality & a lifetime warranty, but not the “Pelican” name brand.
Therefore, all things being equal I would choose a SKB case as it gives you the best value for your money.