'Aquastop' is a coupling that should not be used on high-pressure washers because it has a non-return valve.
The rule generally applies to high-pressure washers and covers all types of water stop systems that must ensure that water does not escape when you disconnect accessories from the garden hose. These go by many different names, but the common denominator is that a non-return valve opens when something is connected, and closes when it is disconnected.
This function gets a lot of strain when used on a high-pressure washer (due to how pressure in the pump head, attached to the valve is modulated), and can thus also be damaged more easily than when in normal use.
When such a connection fails, it can suddenly block water returning altogether. A sudden blockage can cause damage to the pump. The user manuals of most high-pressure washer brands mention the risk of this in one form or another, or they point out that such a valve should be on the opposite side of the hose, i.e. away from the machine.
AVA V4 and V6 pumps also have a function that is usually only found on large professional washers: they reduce the pressure in standby, which increases the life of the pump and accessories. Some of the pressure is released back to the low pressure side of the water system, so here there is an increased risk by having a valve that blocks this relief on the water intake if you have a valve in the way.
Many are afraid of throttling the water going into the machine, but a high-pressure washer only uses a fraction of the water you usually get from a garden hose, and a pump will always have enough water at the start. If there is too little water, the machine's sound changes markedly after a while and you would be able to hear if something was wrong.
We are currently working on translating and rewriting all of our articles into English from the original Norwegian. Whilst we are proud of the quality of our language skills here at AVA, we are aware that there may be some slightly odd syntax and wording present in the articles that have been translated. The approach we have taken to this translation process is in order to get as much information as possible out to our customers in a timely fashion. Thusly the ongoing revision and updating of these articles by our British-Norwegian team will include slight changes to how the text is put together in order to bring it more into line with correct British English.