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Domestic Pressure Washer - Inlet hose keeps blowing off ?

-alan-

-alan-

pfm Member
I bought a little domestic Nilfisk pressure washer today.

Cannot get the thing to work properly - it keeps blowing the inlet hose off when you release the trigger on the lance to stop the flow

The thing works fine and for as long as you keep the trigger in and keep spraying, but as soon as you stop, there seems to be a build up of back-pressure which blows the threaded female connector right off the connector off its male counterpart on the back of the machine. A bit of googling suggests the problem may be down to an auto-stop valve on the brass connections on the hose upstream of the connector.

Finding it impossible to get to speak to anybody at the manufacturers customer service line currently.

Before I go and buy a new set of hose-connectors thought I'd ask if anybody here has come across the problem - and is that indeed the right fix ?
 
I have a nilfisk and have never had this problem. To blow the threaded connector off the back of the machine would take pressure at dangerous levels.

If it is brand new, talk to the vendor.
 
Warning. The following contains many obvious double-entendres:

Get someone to do some spraying for a while and then check how tight the male connector is to the female connector. I can only think of one way this is happening and that is that the connection is loosened as you spray and then the back pressure when you stop is enough to blow it off.

I guess the male connector is round with a few ridges? Try applying a pipe wrench to it and tightening it, without stripping the thread of course :eek:

Cav might not be seeing it because of variations in water pressure at different locations.
 
The inlet connector connects over a rubber O ring usually, sounds like that connector is not up to the job of suddenly taking mains water pressure.
It could also be that the seat of the female part is not sitting to the male part correctly, I have had this with some 'made to look strong' plastic female hose ends, my advise would be try some different ones.
 
Thanks for the inputs and ideas chaps - appreciated

The increase in pressure didn't blow the area around the O-ring section btw - it somehow managed to blow the whole threaded connector off the mating threaded stub on the machine (without stripping the threads strangely.)

I think I've actually found a fix - albeit not fully understanding why .. A bit of further head scratching and then more googling suggested that hose connections with the little internal valves to stop the outflow unless there is a suitable 'male' attachment in place can be problematic with pressure washers.

- I checked, and found the brass hose-connector set I have were indeed so equipped. Took a punch, drill, and a pair of needle nosed pliers to the offending valve and removed it - and everything now seems to work as it should. Haven't fully figured out why yet, but I'll take it as a result in the meantime :)

(I have a sneaking suspicion that when you release the trigger in the lance, there is a momentary rise in pressure internally within the washer before the motor cuts off - and with the internal - possibly non-return ? - valve in the hose connector, the pressure was rising to the point where it forced the connector off. Anyways - with the internal valve removed, there seems to be some mechanism whereby the momentary increase in pressure doesn't get to the point where it blows the connector before the motor shuts down.)
 
I bet it says somewhere in the literature to not use a ‘water stop’ hose fitting on the end that connects to the machine.

Do you have another hose end you could try?

edit - sorry read the question, not your solution, but I’m sure that’s it. Nice work.
 
-alan- said:
(I have a sneaking suspicion that when you release the trigger in the lance, there is a momentary rise in pressure internally within the washer before the motor cuts off - and with the internal - possibly non-return ? - valve in the hose connector, the pressure was rising to the point where it forced the connector off. Anyways - with the internal valve removed, there seems to be some mechanism whereby the momentary increase in pressure doesn't get to the point where it blows the connector before the motor shuts down.)
Click to expand...
There will be a pulse of pressure when you shut the nozzle. This goes back down the chain. Hydraulics being what they are, if you have a rigid non return valve in the system it has nowhere to go and will break things. If there is no restriction back to the flexible garden hose inlet this can stretch to absorb the pressure pulse.
 
stevec67 said:
There will be a pulse of pressure when you shut the nozzle. This goes back down the chain. Hydraulics being what they are, if you have a rigid non return valve in the system it has nowhere to go and will break things. If there is no restriction back to the flexible garden hose inlet this can stretch to absorb the pressure pulse.
Click to expand...

Ah - that could be it. Couldn't figure how having the hose in play reduced the pressure, but 10-15m of relatively soft walled tubing could make enough of an 'expansion chamber' to absorb the pulse.

I knew the collective wisdom on here would figure it out :)

Thanks Steve et al.
 
Wouldn't allow one near my cars, you can cut a brick in half with a decent pressure washer.

Years ago i stripped half the paint from my Morris 1000 van with a pressure washer.
 
A bit like razors then in that respect Dweezil I guess - you can easily cut your arm, or indeed head off with one of those too if you're cack-handed enough :)
 
I am getting things ready - bought the Nilfisk to get the driveway cleaned in readiness for that pristine Por-sha of yours..

You're welcome anytime of course :)
 
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