How to Use/Set Tyre Deflators

Brass automatic tyre deflator on valve stem of mud covered off-road tyre.

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Table of Contents

How to Set and Use Automatic Tyre Deflators

Staun deflators or any other brand of brass automatic tyre deflators, all work the same and are very easy to set.

Most will come with a pre-set pressure out of the box, but it’s likely you’ll want to set yours to a pressure you know will come in handy frequently. If I’m doing a trip that will involve a lot of beach driving, I will set mine to 20psi before the trip, but otherwise leave them set at 28. I find 28 to be a very handy all round tyre pressure that reduces the effect of corrugations, rocks/bumps while also significantly improving traction off-road, compared to the 40psi I run for highway pressures.

Just be aware that most brands of automatic tyre deflators will be available for a specific range. As far as I can tell, these just have different spring rates but if you’re buying new, get ones that will suit your intended pressures. With that said, if you’ve bought them from a 4WD accessories retailer, you should be getting the ones for a standard 4WD and not a truck or a quad. Staun for example, have a 6-30psi range as one of their options. That would be the go for 99% of off-roading.

Set Your Reference Pressure

muddy off-road wheel without valve cap
Knock the dirt/mud off the valve stem first as the exhaust holes in the deflators are quite small and can be easily blocked.

tyre gauge on off-road wheel's valve stem

First step is to use an accurate (or close enough in my case) tyre gauge/deflator to let one of your tyres down to the desired pressure. Here I’m dropping one of my tyres from 40psi to 28psi.

Set Your Deflators to Match the Reference Pressure

You’re deflators will more than likely already be set to a pressure. Whether that’s pre-set from factory, a previous setting from yourself that might need to be changed or they’ve just been rolling around in the glove box and who knows what they’re set to now. They should look something like the below image which shows them partially wound out with some of the thread visible.

Screw the Deflators All the Way In

brass automatic tyre deflator sitting on bonnet

The small ring is a lock nut which holds everything in place once your pressure has been set. Screw that all the way down/in like the below picture.

brass automatic tyre deflator sitting on bonnet

Now screw the main cap all the way in, as pictured below. This main cap is the part that adjusts the pressure setting. By having it all the way in, it will not allow any air out of the tyre

brass automatic tyre deflator sitting on bonnet

Setting the Pressure on Your Tyre

automatic tyre deflator on valve stem

With the deflator now set to where it won’t allow any air out of the tyre, you can screw it on to the valve stem without it changing the pressure on the reference tyre.

It’s then simply a case of winding out the main cap until air starts coming through the vent holes. Once air is coming out, then screw it back in ever so slightly until the air stops. I personally leave it with a minor trickle of air coming through as it tends to be more accurate when deflating other tyres to match the reference tyre. I think that’s just because it’s such a tiny amount of air that it won’t practically result in a lower than intended pressure, but it removes the chance of accidentally winding it back in too far.

The final step is to unwind the lock nut so that it holds the main cap in place. Just make sure to hold the main cap in place so it doesn’t twist while holding the lock nut.

It should look something like the picture below.

brass automatic tyre deflator sitting on bonnet
I forgot to take a photo post-adjustment while it was still on the tyre.

Simply repeat the steps with the other three. Once you’ve got them all set, the next time you’re on the side of the track you can just do a quick lap of the car and put one on each tyre. I do find though, they’re never as accurate as what the manufacturer claims, so don’t walk off to make a cup of tea and do keep a bit of an eye on them. If you’re in a situation where you need very accurate pressures, it might be best to have your automatic deflators set to a higher pressure and then you can manually adjust them down a bit more with an accurate gauge.

These days, there’s so many great options for deflating tyres quickly and accurately. A double deflator with a gauge is going to be a better option for accuracy, which could come in handy on a beach where you want to run pressures as low as possible, without going too far and running the risk of rolling the bead on your tyre. Dual deflators are a great bit of kit, and while the extra expense is a hindrance, I find the biggest down side is that you can’t leave them unobtrusively in a glove box or door for those times when you’re on a more spontaneous trip that you haven’t prepared for.

Bang for buck and for size, automatic deflators, such as those from Staun offer the best value.

How Automatic Tyre Deflators Work.

automatic tyre deflator disassembled to show spring

As you can see above, the adjuster/cap compresses a spring based on how much you wind it in/out.

disassembled tyre deflator showing valve

That spring then pushes down a brass “plug”, that presses against the opening from where the tyre’s air is coming through.

valve and o-ring of an automatic tyre deflator

The plug has an o-ring on it to form a seal.

completely disassembled tyre deflator showing passages that allow the air out

When the cap is screwed all the way in and the spring is completely compressed, the o-ring is pushed firm against the seat and it creates a seal. As you unscrew and back off the spring’s compression, it allows air out until the spring can overcome the pressure remaining in the tyre, sealing again and stopping the deflation from going any further.

Freedom does not come automatically, it is achieved. And it is not gained in a single bound; it must be achieved each day”

– Rollo May, Man’s Search for Himself

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