wallaka":2vbip91z said:
I've never heard that pumps produce pressure......
You are using the equation to try and prove the wrong thing. The pressure is an external factor, not integral to the pump.
I have not responded in the hope that some one else might chime in to avoid what could appear as bickering between us, but that has not happened so I will say my piece then shut up.
I only know how to demonstate this by a mechanical analogy.
A company has an industrial trash compactor. It is the type where a plate moves horizontally to compress the trash against the end of the container similar to the system on a dumpster truck.
On this particular unit, the plate is pulled forward by two steel cables that wrap around the drum of a winch powered by a gasoline engine.
When the compaction cycle starts, the plate is pulled forward from the fully retracted position until it hits the trash. During that stage the winch only has to overcome friction effects so the tension in the cables is quite low.
After the plate reaches the trash, it can only continue forward if the winch increases the pull on the cables. The tension in the cables increases and as the winch is required to provide more grunt, the engine must provide more power and governor opens up the throttle. To continue compressing the trash the winch must provide an increasing amount of pull on the cables. The tension in the cables increases and at the same time you can hear the engine working hard as the governor opens up the throttle.
I doubt anyone would dispute the tension in the cable is created by the winch pulling the cables.
After years of service the gearbox is worn and the cables frayed so the owner decides to replace them. This time he installs a hydraulic ram that pushes directly against the plate, all the necessary hydraulic pipes and controls, and a pump driven by the old gas engine.
Now, when the compaction cycle starts, the plate is pushed forward by the ram from the fully retracted position until it hits the trash. During that stage the ram only has to overcome friction effects so the fluid pressure is quite low.
After the plate reaches the trash, it can only continue forward if the ram increases the force against the plate and this means the pump must supply oil at a higher pressure at the same time drawing more power from the engine. To continue compressing the trash the pump must provide fluid at increasing pressure, and as the pump needs increased power to do this you can hear the engine working harder as the governor opens up the throttle.
Sound familiar, just as the winch applied tension to the cables, the pump generates pressure to force the fluid through the pipes.
Any person still not convinced the pump generates the pressure should install pressure gauges all the way along the lines of a working hydraulic system. The highest pressure will be at the outlet of the pump, and it will progressively fall as the fluid moves along the pipe, around bends, and through control valves. If the pressure is generated by the constriction then it would be highest at the constriction and lowest at the pump.
So, the constriction does not “make†pressure, it creates a demand for pressure that is provided by the pump. If the pump fails to produce pressure or the engine stops supplying power to drive the pump, the system comes to a halt.
And there is a parallel to this which is quite close to home. Your kid needs $20 to go to the movies so you give him a bill from your pay packet. Did the kid “make†the $20, no he created a demand that was provided by the money you have because you worked hard last week. If there is not enough money left in the pay packet or you stop working, there will be no visits to the movies.