how does pressure drop affect volume of flow? i know more pressure drop, more flow. what is the physics behind

Answer 1

Bernoulli's equation.
The idealized case is that there is no loss of energy. When a tank of fluid is under pressure, that pressure represents a potential source of energy. When the fluid is allowed to flow, some of the pressure energy (the "static head") is converted to kinetic energy (the "dynamic head").

The conversion is given by P1-P0 = 1/2 (rho) (v^2)
where P1-P0 is the difference in static head between the stationary and moving conditions of the fluid, rho is the mass density and v is the speed. This applies to liquid flows, where the fluid is incompressible and rho is a constant. Gas flows can be a bit more complicated.

In real flows, the assumption of "no energy loss" is not correct, and the speed given by this equation will be larger than the actual. Nonetheless In many practical situations the error is small and the above equation is still very useful.

Fior greater accuracy, the pressure drop term can be modified to account for friction losses due to piping and fittings.

Answer 2

Maybe you should reverse your thinking. More pressure drop doesn't cause more flow. More flow causes more pressure drop. The pressure drop is a result of pipe roughness, pipe diameter, pipe configuration, presence of fittings and bends in the pipe. You can understand how roughness would impede liquid flow. Think of a creek, with and without rocks on the bottom. The rocks impede flow. Same with any obstructions in the pipe. It takes energy to make liquids in motion change direction. Use of this energy results in pressure drop.

Answer 3

Sounds like the water pressure valve on the boiler has failed. You won't see any leaks because the water runs out through the overflow pipe. This pipe is connected to the pressure valve. The answer is to have the valve replaced. Common fault on most boilers. By the way, all undreground pipes must be protected from corrosion (Even Copper pipes) by wrapping the pipe with "Denzo" tape.