Do you have a well pump on your house?
Imagine if it was pumping something thicker than water.
Molasses is good because its extreme, but honey, or ketchup is Ok if that's easier for you to picture.
Now go open a faucet on an upper floor.
How much would flow out compared to water?
What would the pressure be at the pump?
How 'bout at the faucet?
Repeat the above scenario except open all of the facuets on the first floor as well as the upper floors.
Then take these analogies back to the engine and make it less extreme.
