What’s so important about valve caps?

To begin with, a lot of people don’t know what they do. The fact is, the valve cap is the final seal that keeps air inside your tires.

What about the valve itself?

The core that’s inside the valve stem is only designed to temporarily seal the tire against air loss while you’re inflating it or checking the air pressure. It’s not designed to be the main seal.

Inside your value stems, the value opens and closes, letting air in or out.		If water or dirt get into value stems, they can disrupt the seal, causing the value to leak.		The Alligator V2B value cap is a double-seal, flow through value cap distributed by Myers Tire Supply.

Why not?

Consider what the valve has to do. It has to open when you press on it, then close up again when you stop. It has a little spring inside and a rubber seal that allow it to do that.

Trouble is, as a mechanical device, it’s vulnerable to mechanical problems, often caused by water or dirt.

What sort of problems?

If you leave your valve stems uncovered, as way too many people do, water and dirt can get down into them. Dirt can get into the seals, and hold the valve partially open, allowing air to escape, quickly – or slowly, depending on the amount of dirt.

And water?

Water can become a problem in the wintertime. It’s one of the curious characteristics of water that unlike most things, it expands when it freezes. Get a little water into your valves and when it freezes, it can cause them to open, creating the same kind of leaks that dirt can cause.

And, get enough ice in your valve stems, and you may not be able to add air to your tires at all.

So the answer is valve caps?

Good valve caps. That means a cap that’s metal, with a heat-resistant internal rubber seal. Plastic caps may be good enough for low-pressure automobile tires, but at the pressures used on truck tires, metal is essential.

Besides, metal won’t crack or split as a result of exposure to the sun. The internal rubber seal, of course, is important to make sure the cap actually closes off the valve stem completely, keeping the air inside.

And, you should always carry a few spares.

Why is that?

Because you can almost always get valve caps off, but sometimes, you have difficulty finding them again when it’s time to put them back on.

For a real education, if you haven’t done it yourself, watch a driver checking air pressures in the dead of winter on a snowy day.

First, because the handholes and valve caps are so small, the gloves usually have to come off, especially to get that cap off the inside dual stem. Quickly, fingers get cold and numb, and before you know it, a cap gets away. Invariably, it drops into the snow between the duals.

Now it’s lost in the snow in an awkward spot – in many cases, never to be found again. The driver is frustrated, half-frostbitten, and inclined to give up the hunt. That’s where a few extra caps stored in the tool kit can save the day – and maybe a tire.

And occasionally, there are those situations where the last guy to put the cap on “gorilla’d it” onto the stem (or cross-threaded it), and you practically need a wrench to get it off.

Is there something better than regular valve caps?

In our opinion, there is. Some of our biggest customers use them, and our own experience is that they work. They’re called “double-seal, flow-through valve caps.”

How do they work?

The valve cap contains an internal check valve, somewhat similar to, but simpler than the one in the stem. When you apply the air hose, pressure gauge or air chuck to the valve cap, the air flows through the cap and its internal valve then, through the valve stem into the tire.

What does “double seal” mean?

The cap has a ring-like seal that seals it, like a conventional valve cap, to the valve stem. Then, inside the cap is a second seal that keeps the valve inside the cap closed – until you apply an air hose or gauge.

Not only does this provide a positive seal, but if the core inside the stem should fail, the pressure of air trying to escape actually causes the valve cap seal to seal more tightly, providing additional protection.

What makes these so much better?

For one thing, because you inflate through the valve cap, there’s no need to remove it. If you’re not removing caps, you’re not dropping them into snow or gravel between tires and you’re not having to fish for them.

For another, because this makes checking pressures and adding air easier, it makes it more likely that drivers will actually check pressures and add air.

TMC estimates that it should take only about 20 minutes to check every tire on a tractor-trailer rig. With flow-through caps, that time could be reduced to six or seven minutes. What about dirt and water? Take a look at the flow-through cap we’ve shown here. Notice that the top is completely sealed, and the end has a slight dome shape to shed water and dirt. Can we still use a clip-on air chuck? The end of the flow-through cap is grooved, so your chuck will clip on exactly the way it does to the bare stem. Only with these caps, once you detach the chuck, you’re through, and you don’t have to add the cap. Are these caps expensive? Not in our opinion. When you consider what your tires are worth, and how much you stand to lose if they aren’t kept properly inflated, these special caps seem like cheap insurance. Typical price for these caps is about 62 cents apiece, so you can outfit an entire rig for a little over $11. Do they wear out or need to be replaced? The only vulnerable part, really, is the seals. You should probably replace the valve cap whenever you replace the valve stem. Where can we get these caps? Although there are several different kinds, the ones we’re familiar with and that are recommended by our customers are the Alligator V2B caps, sold by Myers Tire Supply. You can get more information by calling Myers at 800-998-9897 or visiting them on the Internet at www.myerstiresupply.com.