What is the difference between water pressure and flow rate?

Water pressure and flow chart

Written by admin

October 6, 2021

It can be extremely frustrating having to deal with inadequate water flow and water pressure, but there is something you can do to improve the situation.

Even though water flow (or flow rate) and pressure are two different measurements, they are still related to each other.

Water flow refers to how much water comes out of a tap or other fixtures in a specific time.

Water Pressure refers to the force that the water is under to make it move in the desired direction, or the amount of force the water exerts on the pipe and fittings containing it.

What’s the difference between water pressure and water flow or flow rate?
  • Water flow is measured in litres per minute, so it has to do with volume over time.
  • Pressure is measured in bar or PSI (pounds per square inch), so this equation has to do with weight and surface area.

When a tap is closed the flow is zero, but the pressure can be 3 bar for example. As soon as the tap is opened the flow increases and the pressure drops. There is a sweet spot between flow and pressure that is ideal for household applications and various factors influence both. A pressure pump can help homeowners to achieve the desired flow and pressure.

What affects flow and pressure?

Water flow and pressure are both affected by friction. Friction is caused by the inside diameter of the pipe, elbow fittings, height, etc.

As water moves through a pipe, friction will slow it to a certain degree, depending on the texture and diameter of the pipe. The smoother the pipe, the less friction there will be, and the faster water can move through the pipe, provided that the water pressure is sufficient. With good water pressure, the friction in smaller pipes can be overcome so that the water flow remains high.

How do I overcome friction?

A professionally installed water pressure booster pump can help to overcome limiting friction inside a water system.

A water pressure booster pump increases the pressure the water experiences on demand, overcoming friction to be delivered to where it is needed. Because the friction is overcome, higher pressure will also lead to higher flow rates, because both flow and pressure are affected by friction. 

(For illustration purposes only)

For a visual representation of flow and pressure many pumps will have a flow chart, depicting its characteristics under different circumstances.

Homeowners need to find their sweetspot

Pressure is indicated on the vertical axis and flow on the horizontal axis. As illustrated pressure is highest when the flow is lowest, and vice versa. The sweet spot for household water delivery is a balance between flow and pressure and the pressure booster pump you choose should create this balance.

Check out the interview with Pascali’s technical advisor on this very subject!

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