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

• thender
In summary, the conversation discusses the basic relationships in hydraulics and the concept of energy, pressure, and flow. The total energy in a system is the sum of potential and kinetic energies, and energy is a conserved property. Pressure is the force distributed by a fluid over an area, and flow is the mass or volume of fluid per unit time. The flow is related to the pressure differential between two points and the size of the orifice. Restricting the orifice can increase pressure and decrease flow, resulting in a greater force. The conversation also mentions a resource that may provide more information on fluid power basics.
thender
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!

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. https://www.physicsforums.com/showthread.php?t=674896

## What is flow in basic hydraulics?

Flow refers to the movement of fluid through a hydraulic system. It is typically measured in gallons per minute (GPM) or liters per minute (LPM).

## How is pressure related to basic hydraulics?

Pressure is the force exerted on a fluid per unit area. In a hydraulic system, pressure is created by a pump and is distributed through the fluid to create movement or force. It is typically measured in pounds per square inch (psi) or kilopascals (kPa).

## What role does force play in basic hydraulics?

Force is the amount of push or pull that is applied to an object. In hydraulics, force is used to move or lift objects through the use of pressurized fluids. The amount of force is determined by the pressure and area of the hydraulic system.

## How does area affect basic hydraulics?

Area refers to the size of the surface that is being acted upon by a force. In a hydraulic system, the size of the area determines the amount of force that can be exerted. A larger area can distribute force over a larger surface, resulting in a greater force.

## How is energy conserved in basic hydraulics?

The principle of energy conservation states that energy cannot be created or destroyed, only transferred or converted. In basic hydraulics, energy is conserved as the pressure and flow of the fluid is converted into force and work. This allows for efficient use of energy in hydraulic systems.

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