@WH401: Be honest, that's really a vacuum cleaner bag.
@radioman: Inlet restriction gauges aren't exactly precision instruments, but they're not all junk. If something doesn't seem right then double-check it with a manometer; if the restriction gauge is way off then junk it. Your dealer should have maximum inlet restriction specification (in inches of water) for your engine.
@mattman & Hematite: Amen! If your air filters are pluging up too quickly then there are a few things you can do like pre-cleaners/cyclonic separators but simply relocating or raising the air inlet a few feet can help. Those inlet snorkels on some large trucks aren't for fording...
Some thoughts about air filters:
The restriction indicators are important. Every time you pull out the air filter you let a little dust into the engine; it's even worse if you're doing the service at a dusty worksite. Changing filters too often means that you're exposing your engines to this more often than necessary. All that trouble light is truly good for is looking for holes/tears in the element.
I can't abide cleaning air filters with compressed air. You can put small tears or holes in the filter paper and, with dust blowing everywhere, some will get into the filter's clean side. If this is done near the filter box then even more harm is done.
The temptation to use air might creep into your mind when you're on a really dusty worksite where filters last less than a week and the costs start adding up. Fight the temptation and eat the cost of replacing them, add a pre-cleaner or have them professionally cleaned; up here in Canada, Finning offers filter cleaning services.
Actually, a filter cleaner is on my list of shame: The list of things I'd like to make that I haven't gotten around to doing. The idea is stolen from a friend who has what he calls his wall of shame; a bookshelf reserved for books he's bought but not yet read.
