# Basic Hydraulics: Flow, Pressure, Force, Area, Energy

by thender
Tags: basic, energy, flow, fluid power, force, hydraulics, pressure
 P: 15 Hello, I am trying to get a grip on the basic relationships in hydraulics. I do not need the advanced math and engineering, compensation for frictional losses, and fluid viscosity and turbulence effects. Just a good basic understanding. The first concept that comes to mind is the concept of energy, I believe the total energy in a system is the sum of the potential and kinetic energies. And that energy within a system is the conserved property. Like the amount of work that can be done, has been done, and is being done if added up should always be the same in a closed system. Another concept is Pressure. I believe that pressure describes force distributed by a fluid over an area. Force is something that can be measured for a fixed area. Like if I have 100 PSI and apply it to something with .5 square inches, it generates 50 pounds of Force. I consider flow to be the mass of a fluid per unit time that moves past a point. I think that's the volumetric flow rate. A related concept is the velocity of the flow. Flow seems to be related to the pressure differential between two points. And by this point I've lost my grip. Using a basic example, if I open the faucet outside and let water flow out of a garden hose, it will come out steadily, if I then restrict the hose by placing my thumb over the end, the water gushes out violently. I don't believe that restricting the hose with my thumb changes the total energy in the system. I think that the water sprays out farther because its force increased, and its force increased because the same pressure was applied to a smaller area. Flow probably decreased. If I compare a faucet that is only slightly cracked open, it will just drip, compared to one fully open that is gushing, I think the flow is inversely related to the restriction. I'm lost. In the same system I can have high pressure, low flow output, or high flow, low pressure output. So I think flow * pressure = power (conserved). And I think flow is proportional to the difference in pressures and the area. A higher pressure differential should result in more flow for an orifice of the same area. And a larger orifice should increase flow. So flow = pressure1 / pressure2 * area. Thus putting my finger over the end of a garden hose reduces the effective area the pressure differential is applied across, which reduces the flow, and increases the pressure, result - spraying water ten feet. HELP! I need basic working theory!
 P: 584 This might help: http://hydraulicspneumatics.com/eboo...d-power-basics The writing is tailored more towards industrial users, but it should answer many of your questions.
 P: 737 Mass of the fluid per unit time is mass flow rate. Volume of the fluid per unit time is the volumetric flowrate. I wrote a post in another thread a while back which might help a little, too. http://www.physicsforums.com/showthread.php?t=674896

 Related Discussions Engineering, Comp Sci, & Technology Homework 2 Introductory Physics Homework 6 Introductory Physics Homework 1 Introductory Physics Homework 9 Mechanical Engineering 10