- Credit: Cycle Tech

Pneumatic valve springs

Ingenious motorsport technology that's rarely in the spotlight

Ever wondered why even the best of road-legal engines don't rev up as high or as far as an F1 car or a MotoGP bike? There are a plethora of answers to that question but one of them is the type of valve springs they use.

Unlike a plebeian road car, motorsport engines don't have the burden of having to last thousands of miles (except for Le Mans racers but they're not a part of this conversation). The lifting of such a heavy burden allows for some clever engineering to make these engines go even faster. A shining example of said clever engineering is pneumatic valve springs.

First used in Renault's 1986 EF-type F1 engine, pneumatic valve springs eliminate solid springs and instead use highly compressed nitrogen gas to actuate the valve. In simple terms, this removes physical and mechanical limits that were imposed by the spring and allows the valve to be actuated in sync with the timing no matter how fast the engine is running, allowing for a larger rev range, more power and most importantly, fewer chances of the engine failing mid-race. But the biggest issue which pneumatic springs rectify is a phenomenon called valve float. As we all know, springs have a natural tendency to bounce back to their original position after an applied force is removed. In a regular engine, said forces are applied to valve springs hundreds of times a second by cam lobes. The springs have to be soft enough to depress easily and firm enough to retract almost instantly. However, in high-revving motorsport engines, this retraction can sometimes be a touch too slow at extremely high RPMs, which means that the valve is being depressed by the cam before it has retracted to its neutral position i.e. the valve is not able to close fully and the engine is losing valuable compression and thus, power. Not an ideal situation for a sport which relies on the latter.

So how do pneumatic valve springs look? Almost exactly the same as a conventional spring setup, minus the spring. There's not much to describe here, so I hope the images will be more than enough.

Functionally, a pneumatic valve spring is mostly the same as a normal spring but with a few differences. Inside the chamber is compressed nitrogen sitting at about 10 bar of pressure. This chamber is connected via a one-way valve to a huge tank full of nitrogen at 200 bar. Whenever the cam lobe depresses the valve, a miniscule amount of air escapes the chamber and the pressure drops slightly. This is detected by a pressure sensor and the one-way valve opens to refill the chamber back to its original pressure. All of this happens hundreds of times a second and in between valve openings. Incredibly neat system, but what happens when the tank runs out of gas?

Nitrogen tank on a MotoGP bike. Credits: Shifting Gears

Nitrogen tank on a MotoGP bike. Credits: Shifting Gears

This is where the drawbacks of pneumatic springs manifest. The reliance of the entire system on a single component is its biggest failing. If the tank runs out, the engine will be virtually defunct until it has been refilled. There is another problem as well. As stated before, nitrogen is stored in the chamber at very high pressure, which means it's incredibly difficult to keep it there when the engine is not running for extended periods of time. The gas will slowly leak out of the chamber and when that happens, there will be nothing stopping the valve from falling into the cylinder. I don't think I need to describe how horrible that situation is.

So to sum up, pneumatic valve springs are a genius bit of tech that solve a lot of problems presented by conventional springs when it comes to speed and power. But when it comes to reliability, ease of maintenance and most importantly, cost, the plebeian springs continue to reign supreme.

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