In order to under how fluid flows through a pipe, you need to consider two concepts: static and dynamic flow (or pressure).

Other ways in which fluid flow can happen include turbulent flow and laminar - or linear - flow. However, these are less common. Turbulent flow, for example, happens only when there is high turbulence in the water, and involves having the water flow constantly change direction, pressure, and velocity mid stream in the pipe. As a general rule, this is not a common situation with most pipes, especially pipes that reach homes and other residential areas. Dynamic water flow is the stream of water that actually pushes the air molecules out of its way as it moves, while the static water flow is all the other "stuff" that gets carried along with it in its wake (like soap suds). The velocity of water molecules changes as they interact with other molecules. However, the action of dynamic and static pressure ensures that the sum of all the velocity of water molecules results in an ordered motion that will push water through the pipes. Not only does it tell us that matter can change its state, but also that molecular motion can create energy. It is this kinetic energy, or "flow," that carries the water molecules through the resistance they meet in a pipe and helps liquid flow through a pipe. It is also what makes a raindrop bounce off the sidewalk rather than soak in and join the molecules of cement. The motion of water can be manipulated by changing the shape or position of what the water flows through (just watch what happens to a stream as it flows between two rocks), but this does not change its molecular behaviour.

How do water pressure and flow work?

Water flow and pressure is due to the molecular motion (kinetic energy) present in water. The faster the molecules are moving, the greater the pressure created as they hit against a wall (generally a pipe wall if the water - or other liquids - are flowing through a pipe) or another object that is trying to stop them.

Water flow

When there are molecules with an excess amount of kinetic energy (water), these molecules will overcome any resistance and continue its travel at full force until it reaches a new position where it can slow down (like a circular pipe wall) or find equilibrium with its surroundings.

What does water flow depend on?

Water flow depends on several different factors such as the shape/size of the container holding it, gravitational pull, temperature differences, and air pressure just to name a few. For example, if you have a container that is long and narrow, the speed of fluids flowing will be faster because there is less resistance and high flows of water will be more common. If water flow is measured at the same depth in two different containers (one tall and skinny and one short and wide), then there will be more water flowing through the long and skinny container than there is water flowing through the short and wide one because there isn't as much resistance or friction in this scenario.

Definition of water pressure

Pressure is defined as a force per unit area. The SI unit of pressure is the Pascal (Pa), which represents one Newton per square meter of surface area. Every point in space has an associated pressure, and while it may not be possible to measure this pressure at all points in space, almost any location can be represented by some combination of several pressures.

How do I find my water pressure?

The easiest way to measure your water pressure is with a handheld gauge that can be easily attached to the main water shutoff valves. This will allow you to see what the pressure is at all times, but keep in mind that this reading will be influenced by whether or not any appliances are running.

Another common method involves installing a pressure gauge just before the entrance of the cold-water pipe on your plumbing fixtures and appliances. This is useful for measuring how much "head" (pressure) you have available for an appliance. It also offers the added benefit of hampering a potential leak while preserving water flow through a pipe and through most taps and toilets without slowing down the flow rate noticeably.

How do I repair low water pressure?

There are several ways you can repair low water pressure, but the best way to fix this is to replace any worn-out parts like washers or any other materials that will allow for increased flow. Locate and determine the cause of the problem then repair it.

If you have a small hose leading from your garden pond or spigot into a bucket in order to fill up your water tank/reservoir, check the hose first. Common areas where leaks occur are joints between hoses and threaded fittings. If you have a water pressure pump, check to see if this is broken or damaged in any way.

You can also check your owner's manual for help. Most manuals have a figure of the product (like a pipe, pump, hose, etc.) with all the parts labelled. You can refer to this figure to make it easier to check each part and figure out where the issue is.

Simplifying Bernoulli's equation

Bernoulli's equation is a mathematical equation that predicts how pressure, velocity, density, and flow interact with each other. The formula takes into account several factors, including:

  • Fluid mass density.

  • Acceleration due to gravity.

  • Pressure, velocity, and height of the fluid in a pipe.

This equation only applies to non-viscous fluids. Viscosity is essentially the opposite of flow. It considers how resistant a fluid is to changing shape when flowing through something like a piping system - the higher the viscosity, the greater the resistance. Viscous fluids are ones that allow what they flow through to stick and become embedded into the flow of the mass resulting in friction just like the wind does when it flows past your body at high speeds. In order for this equation to work, there must be no friction caused by another substance forcing its way into the natural flow of water around or through an object. Friction also results in energy loss, which reduces the speed at which the fluid is flowing inside pipes. In order to get more energy in a pipe system, the pipes must be cleaned regularly. Adjust the pipe run to prevent sagging, insulate the pipe, and use better quality materials. You should also improve your pipe system's efficiency, which will ensure the fluids have far more energy than if the pipe system wasn't optimized. The equation also holds that if a small volume of a liquid is flowing from an area of high pressure to one of low pressure, there is more pressure behind than in front. This helps increase how fast the fluid is flowing. It also states that when the flow is incompressible, the density is constant.

How do I use Bernoulli's equation?

Bernoulli's equation allows the calculation of several aspects related to the speed, pressure, and shape of an object. In relation to water, the equation can be used to determine the pressure at a certain point in a fluid given information on the speed and shape of a section of the fluid. This is helpful when determining how water flows through a bendy pipe like the ones found within the plumbing.

Additionally, after you have the measurement of the speed of the fluid flowing in the pipes, it is possible to then reduce the flow's diameter. The lower the diameter, the more the rate of flow increases.

Furthermore, since a lower diameter means a smaller pipe, this will also result in higher pressure, where a larger pipe size would result in pressure loss and lower pressure (keep in mind that higher water pressure will also result in an increase in pipe thickness, which may be a concern for some people). This is because a smaller cross sectional area results in the pipe pushing high flows of water to your taps, while a larger one will allow the water to flow uniformly.

The advantage of considering water with Bernoulli's equation in order to increase pressure is that you don't need to worry about the effect of it being compressed. Water is essentially incompressible, so no matter how small an inlet it is forced through, it will not compress so much that there is any danger, unlike several other fluids. If you are after an easier description of Bernoulli's equation, NASA has a quick guide.