This is NOT a "problem", it's a rather a question. Let's say I've got a vacuum chamber, and I suck the air out of it using a vacuum pump that is capable of doing -200 Kpa. Let's also say that there is a valve on this chamber. After a full vacuum has reached, I open this valve WHILE the pump is still running (thus creating a suction at the valve opening). What would be this pressure of suction? Is it -100 Kpa (100 Kpa which is atmospheric pressure, subtract 200 Kpa which is pump capability) OR is it just 0 Kpa since we are at vacuum?