Air Supplies Handy Guide to Everything you Need to Know about Pressure and Flow

When looking for a power washer, it is often hard to find the right model, as there are so many different options out there. 

psi guage

With pressure cleaning becoming an increasingly popular way to clean driveways, house facades, cars and pretty much anything else, more and more manufacturers are putting their own models on the market. This means there are some superb models out there, but also some very sub-par setups that just are not fit for purpose.

Pressure and flow ratings can also create confusion, as most people are unaware of what these ratings mean.


When it comes to power cleaning, pressure is obviously an important part of the equation.

Many manufacturers make the entirety of their selling platform the pressure that their power washer produces. However, these ratings are often misleading. This is because manufacturers will state the maximum pressure their power cleaner can perform at, but that does not always translate to the actual pressure or cleaning power you will receive.

This is because pressure is only half of the story when it comes to cleaning.

A true indication of a power washer’s capabilities comes from its flow – measured in litres per minute (Lpm) and Bar – the pressure it produces.

  • Pressure ratings – often overstated by manufacturers – are just a part of what you need to know
  • A real measure of a power cleaner’s capabilities is the combination of its flow – measured in litres per minute (Lpm) and Bar- the power the washer will generate when cleaning.

Bar is the measurement given to a unit of pressure, with 1 bar equal to 14 pound per square inch (PSI). As a general rule of thumb, the higher these ratings are, the more powerful the power washer is. It is important to think of these two ratings – Lpm and Bar, as mutually important – one can be high, but if the other is low then you are likely in for an underwhelming cleaning experience.

For example, a usual car wash with a power cleaner will require around 1820 psi at 10Lpm, whilst cleaning a driveway needs 2100 psi at 14Lpm.


The flow rate of a power cleaner – measured in Lpm, has as much impact on cleaning results as the pressure rating.

Flow rate can differ greatly depending on the level of the cleaner. A DIY power cleaner, available in any hardware or high street store will usually clock in at around 6 Lpm at the lower end rising to around 10Lpm. An industrial model could offer Lpm rates of 10 to 40Lpm, depending on the application.

This is obviously quite a gulf, but most DIY users have no need for the power that industrial power cleaners provide. A well rated and balanced power cleaner in the lower, DIY range can provide all of the cleaning force that most home users require. Stripping paint with power, for example, requires 14000 psi, which presents real dangers if misused and should remain in the hands of experienced, trained professionals.

  • DIY power cleaners tend to fall in the 6-10 Lpm range
  • Industrial models deliver 10-40 Lpm
  • Higher rated power cleaners can cause real damage – to property and persons, so should remain in the hands of professionals

Pressure and Flow Together

Because there are so many different models of power cleaner on the market, working out there difference between them is a difficult task.

Ultimately, everything comes down to performance for price – everyone is searching for the very best performance for the cheapest price. A good way to work out the power differences between two power cleaners is by using a simple calculation.

Known as the ‘cleaning effect’ in the power cleaning business, it is how businesses work out just what they are getting for their buck:

The Cleaning Effect Equation: Pressure (In Bar) x Flow(In Lpm) /600


This calculation is not something that features on manufacturer’s boxes, but is a rough, reliable measuring stick for the power you can expect.

You can break down the results of the calculation by the following levels, which will tell you just how good the power cleaner you want it:

1.0 - The cleaner is nothing spectacular, but useable.

1.5 – A reasonable power washer that can handle medium-level tasks

2.0 – A top-class domestic power cleaner.

2.3+ - A hire shop machine, this will deliver all the power you could probably need for any home-based, DIY task

The key to picking the right power washer is finding the perfect cost-to-power ratio for your needs. Buying the most powerful model available does not mean the best value; it may simply mean that you have a power cleaner way overmatched for your needs.

Assessing the right cleaner for the right job is essential. Just as an industrial cleaning crew would not use a low-powered DIY set-up, there is no need for DIY users to go for raw power.