Steam does escape, through the vent, otherwise pressure would increase to enormous levels. The vent is just controlled by a weight so it only lets out enough steam to keep the pressure at about 12psi in my case. I thought condensation on the lid would replenish the water, but the lid was >100C so I guess that didn’t happen.
I fried up the onions and chili, then dumped in raw chickpeas, two cartons of chopped toms and a bit more water than I’d usually add, it was a bit thick soupy, to avoid the sauce sticking to the pan whilst I boiled it up to pressure.
It worked a treat. It reduced a bit, the dal is on the runny side of acceptable, the chickpeas are much softer, smoother and more mellow tasting than usual, and the sauce is fruity and tomatoey. 20 mins, and the chickpeas had only been soaking for 6-7 hours.