There is a great deal of confusion as to what the internal pressure of tennis and paddle balls is. In many pages it is said that the pressure is around 12 – 14 psi, depending on the brand and the use of the ball and in some others it is maintained that it is much higher; from 26 to 33 psi, also depending on the use and brand.
How is it possible that there are such large discrepancies? Who are right? The ones that claim they are 14 psi or the 33 psi?
In this article we are going to reveal it with reliable and scientific evidence. Let's go for it:
To begin with, we will say that in the regulations on tennis balls there is no concept of pressure, only rebound. All types of balls, except those used in extreme altitude conditions, must bounce between 1.35 and 1.47 m when dropped from a height of 2.54 cm (100 inches) onto a concrete floor. The tennis regulations do not speak at any time of internal pressure of the balls, so, as long as they comply with the measurements, weight and rebound, they will be suitable for the game.
Regarding the rebound, the paddle tennis rules establish similar values, with two centimeters less rebound at the upper threshold of the range, that is, a paddle ball dropped from a height of 2.54 m must bounce between 1.35 and 1.45m.
In paddle tennis, however and surprisingly, there is a rule on the pressure of the balls, which must be between 4.6 and 5.2 kg per 2.54 cm2, that is, a theoretical pressure of 25.7 and 29 psi, which, as we will show later, is completely impossible unless these figures indicate absolute pressure = internal pressure + atmospheric pressure.
We summarize the data in this table
The first thing we notice about this impossible rule about pressure is that it is given in a mixture of units. Pressure is usually measured in kg/cm2 or psi (pounds per square inch), which are the units used by the International System and the British Imperial System, respectively. Since paddle tennis is derived from tennis, a sport created in England, it would seem logical that the pressure of the balls be given in psi. However, for some reason unknown to us, the people who wrote the padel regulations (original sport from Mexico but developed in Spain), decided, probably due to some confusion, to give a pressure value in kg/ 2.54 cm2, something never seen before and that probably comes from the equivalence of an inch, which is 2.54 cm. One square inch is therefore 2.54 x 2.54 cm2 = 6.45 cm2.
At this point, it is worth asking why they chose those values of pressure. We imagine, although we cannot say for sure, that the regulations must have been written in the 70s and that it was written in relation to the balls based on the tennis regulations of that time since there were only tennis balls to be able to play tennis. paddle, as they were not manufactured specifically for that sport.
Since no internal pressure is specified in the rules of tennis, we imagine they went to the literature and found that most tennis balls are pressurized to a relative pressure of 12-14 psi, which is equivalent to a absolute pressure at sea level of 12 + 14.7 = 26.7 – 28.7 psi, a value very close to that indicated in the paddle tennis regulations.
In addition, to demonstrate that the regulation must refer to the absolute pressure of the balls, we have proceeded to measure the relative internal pressure of the pressurized cans and the balls with a manometer to which we have attached a needle to pierce them. As you can see in the video, the pressures obtained do not exceed 14 psi in any case.
We hope that this article and the demonstration videos have clarified once and for all the matter of the pressure of tennis and paddle balls. All the best.
The Ball Rescuer Team