Pressure Cleaner Service Fundamentals

This story is contributed by John Hales, Chief Engineer at Aussie Pumps, who has played a major role in the evolution of the Aussie Pump Scud range of cold water pressure cleaners in the 3,000 psi to 7,000 psi range. These machines are highly regarded not just in Australia but with exports to many countries around the world.

Being asked to write a story about this subject is no easy task. It may have to turn into a series! Our purpose is to take the mystery out of high pressure pump technology by showing in simple and easy to understand terms just how this high pressure system works – the pitfalls, potential dangers and practical advice on how it can be effectively used. And, the best way to tell it is from the point of view of our own experiences at Australian Pump Industries.


When we decided to start building pressure cleaners, we knew there was an already overcrowded market. The logic from there went that if we were going to be in the game, we had to do it better and give users something that was an improvement over those machines that were already available.

By looking at the competitors we saw there were a lot of European machines, some cheap Chinese units and existing manufacturers who have been in the game for a long time.

To challenge that, we knew we had to give something extra to people who were already using the equipment. We found that our first priority was going to be the pump and products that delivered more in terms of longevity, performance and value for money.

The result was an exclusive relationship with Bertolini pumps in Northern Italy. Bertolini is a great company, producing a range of triplex pumps – all the way through to 15000 PSI (1,000 bar). 

Aussie Pumps Hamish Lorenz shows a solid ceramic piston. Note the fins on the Bertolini pump.


  1. We call them ‘Big Bertys’ because they’re built with strength and quality. They have premium oversized bearings for extended pump life.  
  2. They have extra long forged steel crankshafts, providing a solid coupling for pump and motor (engine).
  3. They have oversized con rods for extra strength and easier lubrication.
  4. Large stainless steel Martinistic plunger rods are stronger, harder and smoother and provide longer seal life.
  5. They have high quality ceramic pistons for years of uninterrupted high pressure performance. That’s an important factor. You’ll see some products advertised with ceramic pistons that are in fact not ceramic pistons at all. They are stainless steel pistons with what they call the ceramic coating. It’s a much cheaper solution but it doesn’t have anything like the wear characteristics of solid ceramic. 
  6. Bertolini developed an exclusive ‘double V’ and ‘double U’ self-lubricating packing seal.  They have an elastomer designed to prevent water from contaminating the oil in the crankcase and provide years of leak free operation.
  7. Bertolini design ‘rapid action mirror finish’ 316 stainless steel check valves. That means no corrosion, as opposed to cheap grades of stainless that provide real problems down the track.
  8. Low stress valve caps are unique to Bertolini. They put the sealing ring at the bottom of the thread of the valve caps, not at the top.  This keeps any leakage from the high pressure water chamber in the pump from getting into the threads.  That solves a problem before it begins.
  9. High efficiency brass head, thicker walls to withstand high pressure.
  10. New “cool fin” Smart crankcase and pronounced fins for extra cooling. Lower running temperatures extends pump life!  

We also like the idea that the ‘Big Berty’ pumps were available for a gearbox engine drive with 4000 psi pump. At the time when we got started, 3000psi was the norm. We built the first 4000psi heavy machines in the market. They offer top quality accessories and first world Honda twin cylinder engine. That extra grunt surprised the market.


The simple explanation is that the pressure produced in a pressure washer system is the result of forcing a known volume of water through a restricted orifice (the spray tip).  This pressure is measured in bar or pounds per square inch (PSI). 


The flow is determined by the speed that the pump shaft is rotated (RPM). The faster the shaft is rotated, the higher the output volume. This water flow is measured in litres per minute. Thus, the operation is simple – the pump draws water in through a series of inlet check valves as the plungers move back. As the plungers move forward again, the Inlet valves close, forcing the water to travel through a series of outlet check valves and to the pump.

The water exits the pump and the direction of flow is controlled by means of downloader or regulator valve.  The positive displacement pump always delivers a certain volume of water regardless of whether the gun trigger is open or closed. The unloader controls the direction of flow either to the gun or, when the triggers are closed, directing the by-pass fluid back to the inlet of the pump. 

Every pressure cleaner operating with a gun system must have a pressure relief valve. We use only the best from a company in Northern Italy called PA, who are second to none in terms of quality. We use their unloader valve all the way through the range from our 4000 PSI Scud all the way through to our 7000 PSI Raptor machines. 


Setting the unloader valve for the required pressure of the machine depends entirely on the correct nozzle selection. The correct nozzle orifice can be selected to suit any specific pressure flow combination. We produce a great chart on this that makes it easy for operators to make the right selection.

We tell everybody that nozzles wear. That’s because water is abrasive and over a period of time, the orifice in the nozzle will get larger, resulting in a pressure drop.  Changing nozzles regularly is an inexpensive way of keeping the machine operating at its maximum rated performance.  

Nozzle sizes are based on the capacity of the machine being coefficient with pressure. Nozzles are available in a wide range of angles, depending on the type of job being done. We standardize on 0 degrees for laser-like cutting applications, while 15 degrees and 25 degrees are the most common. 40 degrees is also an option where large flat surfaces are to be cleaned. 

An explanation drawing on how the high-pressure circuit works is shown above.

You will notice there are other components mentioned. They include suction filter (essential), a safety valve (also essential) are standard equipment on all Aussie machines as well as a top quality high pressure gun/lance combination. 

Users and suppliers need to be conscious of using quality high pressure hose and guns sized and specified correctly for the machine’s capability. In other words, you don’t use a 3000 PSI rated gun and hose with a 5000 or 7000 PSI rated machine.  That can result in serious injury and of course nobody wants that.


Over the next months, we will be producing a series of this article moving more into product selection, horsepower calculations, and of course, safety.  This is one of the most important factors in using pressure cleaners. Ultimately, as we get towards the end of 2022, we will move on a continuous dialogue on specific application recommendations and high pressure accessories.

Copies of our free Aussie Blaster Service Fundamentals booklet is readily available, along with our safety training course online. 

For further information, contact John Hales at Aussie Pumps.