As I know that before Galileo,all the scientists believe that vacuum cannot exists. But how suction pump(which itself remove air)was discovered before Galileo. What was the steps involved in it to make suction pump?
Aristotle believed that no void(vacuum) could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void. Even in his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular.
But much before Galileo, in the 13th and 14th century, considerable attention was given on these issues by European scholars such as Roger Bacon, Blasius of Parma and Walter Burley . Eventually following Stoic physics in this instance, scholars from the 14th century onward increasingly departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion widely acknowledged by the 17th century, which helped to segregate natural and theological concerns.
Using geometry, Ibn al-Haytham(965–1039) mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī also states that "there is no observable evidence that rules out the possibility of vacuum". These steps led to the making of suction pump which appeared in Europe from the 15th century.
Thus, it is not true that scientists before Galileo did not believe about the existence of vacuum or void but were aware of it.