Instead of saying a %, like 40-100-125% pressure, it should be 40-100-125 pressure, pressure units, or psi. Purely flavour, but it is more intuitive.

As is, 40% pressure of t1 pipemeans, I believe, is 40% of the pressure of a t4 pipe. If you said it had 40 pressure, or pressure units, (though pu is already used for pollution units I believe) or even just use psi. Sure, not accurate as you said before, but you don't use steam temperature either.

Letting you describe a pipe as having a min pressure of 0 and max pressure of 40, while a tank has 0-125 makes more sense than using a t4 pipe as an arbitrary seeming baseline.

Also valves. Instead of 75% pressure to overflow, say that a source pressure of 75 psi causes it to overflow.

The purpose is to allow easier explanation. Percentage is always used for a fraction of something else, which is either universal, a common unit, or another measurement explicitly stated. When I tried to explain it, I often had to explain that the percentage part is basically exposed internal code, and then translate it into an arbitrary measurement, to avoid percentage multiplied by percentage of an arbitrary value