Any pressure washer that uses a trigger mechanism or valve to stop the flow of water must have an unloader valve fitted.
If the trigger is not pulled or the flow of water is stopped due to a blockage then the unloader valve will come into action – it allows the flow of water to be redirected back to the inlet side of the pump or to an external tank instead of to the nozzle. This means that the water has still got somewhere to go and prevents the motor from stalling and damage being caused to the motor or pump unit. When the unloader valve senses the trigger is being pulled again, it should then allow the flow of water to the nozzle again.
Some machines are setup to bypass back to the inlet side of the pump, meaning that when the trigger is not being pulled the water is continually flowing from high to low pressure or “ in a loop ”, the problem with this setup can be it relies on the users expertise – water which is bypassing in this type of loop will get hot over a period of minutes due to the transfer of heat from the pump, which if left long enough can do damage to the pump itself Therefore with this type of system it is important that the machine is not left idling, or bypassing for any period of time ( we usually recommend no more than 2 minutes ). There are several ways around this problem, for example we produce a version of machine which will shutdown after 2 minutes of inactivity thus preventing damage to the pump. Another solution to the problem could be to have the unloader bypassing back to an external tank from which the machine itself is drawing water, the type of setup we use on our engine driven machines – however this solution cannot be used if the machine uses high pressure chemical because it would fill the tank with detergent and is not ideal if space is at a premium.
Types of Pressure Washer Unloaders
There are two main types of unloader, a trapped pressure unloader valve which means that when the user lets go of the trigger mechanism that there is always pressure in the high pressure hose, even after the machine is turned off, until the trigger is operated again. Some trapped pressure unloaders may have a pressure switch built in to allow them to be used on machines featuring a total stop / start system, i.e. the machine stops when the trigger isn’t pulled and starts as soon as the trigger is operated again.
The other main type of unloader for pressure washers is the flow sensitive unloader which bypasses water when it senses the flow of water decreasing between itself and the trigger. This is the type of unloader used on our Britclean 3000 SSH timed shutdown machines and means that once the machine has shut off – there is no pressure in the high pressure hoses and they are safe to disconnect. The only downside is that unlike a trapped pressure unloader, you can not reduce the flow of water by reducing the nozzle size, because the valve will sense it and go into bypass mode.
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To summarise, each unloader has its purpose, fitting the wrong one could result in your machine not working correctly and damage to the components, so if you are in any doubt as to which unloader you require please contact us with the details of your machine and we will be happy to advise you.
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