There is no need to explain the popoff valves (also called pop off ventil, dump valve, diverter valve, bypass, power pop etc.) so I will not go into boring details.

There is plenty of information on the Internet and various forums, which cannot be consulted by just anybody and is readily available. I will simply provide some technical information, in as clear and simple way possible, so that even unspecialised people are able to understand what I am saying and at the same time attempt to fill in some gaps or complete the information for those who know a bit more. You may be asking why I am writing this article; let me tell you straight away! We spend a great deal of our time giving answers and information to those who ask us “ what do your valves sound like? “. It is certainly not easy to answer this question over the phone. So we have decided to put it in writing!

The first thing people should know about popoff ventil, dump valve, diverter valve, bypass, power pop et is that their acoustic features are very similar to a musical wind instrument, which can be conformed to the passages of air in the best way possible and made of suitable material to be able to produce resonances and vibrations and can be tuned to perfection…but whatever it will ever be able to produce will always be a sound based on the quantity and pressure of the air that passes through it. Logically speaking, the more air and higher its pressure, the stronger the sound will be and vice versa.

Having said this, we now understand that the sound and the hissing of the popoff ventil, dump valve, diverter valve, bypass and power pop, is not 100% due to how they are made. We still have not established what the percentage of the valid component is in judging the special features and goodness of the same. If we were to install a valve in a vehicle with aspirated engine, what would the results be? Absolutely nothing at all! No turbine produces air! So, at this stage, should we say that the goodness of the sound or of the hissing produced by the pop off valves is 100% due to the vehicle on which they are installed and proportionally to the overfuelling pressure? This too would be a rough statement, because if we had a valve made of poor materials, with unsuitable sliders inside and maybe not even self-lubricating, there would certainly be high levels of friction, such to create opening delays, thus preventing the air from producing the beneficial hissing effect. This is because, when a valve opens with a delay, instead of passing through its orifices, the air bounces like a ball between the three opposite ends (accelerator throttle closed, air filter box and compressor impeller).

This bouncing phase also produces a sound, which many people, or rather too many people, mistake for the sound created by the popoff ventil, dump valve, bypass, power pop valves etc.

If you go to this link you can hear the sound of a valve that is too restricted. It opens initially and hisses for about half a second then it is saturated with air and, not being unable to vent it, it starts to bounce between the accelerator throttle closed, air filter and compressor impeller. Those who use it are however convinced that it is the sound created by the valve, when it could be simply eliminated to have the same dangerous sound. In fact, when people contact us to purchase a valve, they are indeed looking for this sound; we therefore have to make them realise that the sound is not the valve opening, but a valve that does not open at all or opens way too late compared with the pressure wave that should pass through it, or with the orifices not open enough for the amount of air that should pass through them.

This can happen (as we said earlier) due to a valve that is not designed properly or that is built incorrectly. It also happens when you want to fit a pneumatic valve on a vehicle where an electric valve is installed standard.

If you go to this link you can hear another example of a pneumatic valve fitted in the place of an electric valve. In this case, you can clearly hear the air bouncing without any opening through which it can vent externally.

To provide complete information, you should be aware that when we are speaking of electric or pneumatic valves, we always mean valves with the same identical functions.

The differences are merely in the opening command.

In the electric valve, there is a magnet that is energised by the flow of current, which pulls a plunger toward it, which in turn opens an orifice where the air to be vented passes. The discharge may be open (valve with hissing) or closed with recirculation (silent valve).   In the pneumatic valve, the opening and closing command is given by a small tube that has to take pressure and vacuum to fill or empty a chamber with either a diaphragm or a piston inside it. In the pressure phase, the force of the same applied on the face of the piston or diaphragm, keeps it pressed down, closing the venting orifice, while in the vacuum phase, on the face of the piston or the diaphragm, a negative force will be applied that pulls upwards, thus freeing the orifice below and venting the air. Having said this, it is clear that the electrical execution speed is way higher than that of air. For even further detail, we will also explain why there is this delay.

In all the following explanations on the operation of the valve, we intentionally do not mention the contrast springs, which are a part of the valve closing system. Relying on the fact that the manufacturer of the valves has considered the spring as an essential element for closure and for hissing, because this option has to be controlled with the clearance of the sections and of the diameters in the design phase, avoiding other inappropriate adjustments.   In the electric valve, the control unit sends a current pulse to the valve and it opens in real time as the current arrives.(delay equal to little more than zero). The response time can be compared with when we press on the horn to when we hear its sound.   In the pneumatic valve piloted by the control unit, the control unit sends a signal to the solenoid valve, which switches the pressure/vacuum waves, which must then reach the valve. So, if there was pressure in the valve before, the circuit must first be emptied of the pressure and then it must be saturated with vacuum and vice versa in the closing phase.(delay of approximately slightly less than 1 second)   In the pneumatic valve piloted by the phases of the engine or by the closure of the accelerator throttle, the pressure in the suction manifold (with the turbo running), is taken by the customary tube to the valve, which remains closed due to the pressure. Then, when the throttle closes completely and the wave sign changes in the manifold and switches to vacuum, the same is taken to the valve, again through the tube (opening it). In this case, in addition to the air movement delay, the engine is also slow in changing the wave sign, because the closure of the throttle does not cause a sudden change in sign, because the engine must first intake all the air of the manifold, then by continuing to turn, it has to intake the same amount to send as vacuum into the space of the manifold (delay of slightly more than one second).

There is a third type of valve with a different control system, namely that with pressure both above and under the piston. The two pressures are the same and keep the piston still. Then you simply eliminate the pressure above so that the piston rises as it is pushed by the force of the pressure below.

Considering that the speeds of the air inside the engine are near to that of sound………..it is easy to understand that opening delays are definitely to be avoided.

Over the years, engines have gradually become more and more powerful and with greater torques, but without increasing the displacement and without exaggerating with the overfuelling pressures. This has been achieved by studying the materials thoroughly, as well as the frictions and above all the volumetric filling. Designers have managed to make the engine take in more air by improving the venting and admission lines, taking the speeds of the air and the pressure waves favourable for filling to truly high levels, compared with some years ago. These speeds also require quick controllers to be managed and maybe not completely with feedback system, as they were in the past, especially with regard to overfuelling. Starting from electric or electronic waste gates, continuing with the accelerator throttle completely freed from the decisions of the foot of the driver and convinced to follow the program set and continuing with the pop off valve, which in the meantime has become electric (the command).

Now, having understood all this, an old pneumatic valve can be installed where there was an electric valve. However, in terms of performance and settings, it is definitely counter-productive. Would you be willing to swap your smart phone with a mobile phone of just 2 years ago? Maybe I should stop here, as I think no other comments or explanations are necessary!  

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