A flat tyre can be upsetting and frustrating. A tyre can go flat from a variety of things: a puncture in the tread or sidewall, a broken bead seal or a faulty air valve. Over time, a valve stem seal can grow weak or crack and air will leak out of your tyre quickly. Replacing a tyre valve is fairly simple process and well worth the £6 to £13 you will save by not taking it to a mechanic.
Remove the flat tyre from your car. Lay the tyre flat on the ground so the side of the tire the valve protrudes from is up. Kneel onto the side of the tyre, with the section where the valve is between your knees.
Pry the tyre away from the rim with the flathead screwdriver.
Grab the exposed tyre valve with the pliers and pull it down and out.
Take the old tyre valve to your local car parts shop and buy the exact same valve.
Squirt a half-teaspoon of washing up liquid onto the new tyre valve. Rub the soap over the entire valve. The soap will act as a lubricant to help the valve slide in and once it dries it becomes a sealant.
Kneel back onto the side of the tyre. Push the new soap-covered tyre valve through the hole you pulled the old one out of. Grab the top of the valve you pushed through the rim with the pliers and twist on it while pulling it out; this will ensure you got enough of the valve pulled out and will secure the soap seal.
Stand up and let the tyre raise back up to the rim. Wrap the strap ratchet around the circumference of the tyre. Ratchet the strap until it becomes tight and the tyre inner bead begins to touch the rim. Inflate the tyre through the new valve to the proper pressure with an air compressor. Put the tyre back on the car.