DNA stores the genetic memory of an entity. RNA transports that memory to where it needs to go. For a good breakdown of the difference between the two, scroll down to the related links and check out that site.
The hot water supply valve you turned off to allow you to cut into the hot water pipe is still turned off. This valve was probably an old gat typr valve that failed in the closed position and although the handle moved the mechanism insid did not. This is a common failure with that type of valve.
The proper suction pressure of any air conditioning or refrigeration system is determined by the type of refrigerant used and sometimes the amount of charge. : Suction pressure used is also directly related to the temperature required. : The temperature required in the evaporator relates to the pressure required in the suction line since, the fluid is at saturation in the evaporator. : Knowing the temperature required, use the fluid's saturation tables to find the corresponding pressure required.
This is all thanks to Air pressure and water pressure. Lets say that you are drinking water from a glass with the help of a straw. When you suck at the straw, you are essentially drawing air out of the straw. This decreases air pressure which was in the straw right above the level of the water. In the mean time the air pressure around your glass of water is constantly pushing the drink level to go down. And the water pressure of your drink is pushing the water level to go up. Since you just helped decrease the air pressure in the straw, the water finds an outlet and thus goes up the straw till it reaches your mouth.