Quote:
Originally Posted by entwisi
To me pushed infers that 'positive pressure' is in action.
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It depends where you are. In the cylinder you have negative pressure relative to outside it, outside the engine you have positive pressure relative to inside it. The air will move from a high pressure area to a low pressure one. That is why the air is pushed in. It's still works the same way in a turbo charged car.
You would not say the air is sucked out of you tyre when you press the valve in. The air will move from the high pressure inside the tyre to the low pressure outside. The word suction is commonly used when pressures under 1 bar are involved.
In the end it comes down to using the scientifically correct words. As in a bulb is where daffodils come from whereas light comes from a lamp. It does not really matter which way you describe it. They put that question in to catch people out.
I was discussing this with my mate, an ex fireman. He said they were always taught that if you are pumping water from a pond, the pump does not suck the water out of the pond. Atmospheric pressure acting on the surface of the pond pushes the water into the low pressure area created in the pumps inlet pipe.
The input to a pump is commonly known as the suction side and the output is known as the pressure side. That's stupid English language for you.