Non-return valve when using a pressure washer

Not a lot! What are you expecting to happen?

I think that, legally, you're supposed to use a double check valve when using hosepipes etc. outside to avoid any danger of dirty water getting sucked into the mains system in the event of a mains failure. I would have thought that the risk of that was negligible when using a pressure washer.

Thanks for that - I wasn't expecting a lot to happen, but as it is mentioned in the instruction book, and I couldn't find one locally, thought I'd see if I could get someone knowledgeable to advise.

Thanks

Graham

Not so much a mains failure, as the gentlemen in large red trucks turning on their pumps. A hose filling up a swimming pool or a pond can easily suck the water back into the mains unless a non-return valve is fitted. This is less of an issue with a pressure washer because the end is usually not dipped under water.

Yup, its just to comply with the water board regs.

Plus a set of inlet & outlet valves! Back siphonage virtually impossible.

A water authority plonker once told me, after admitting that back siphonage was about as likely as a lightning strike, that if the water main were shut off, the suction from the pressure washer could cause a 6" plastic water main to collapse.

He didn't specify what size pressure washer might be able to do this - I reckon about 500hp :-)

On 31 Dec, 17:26, "The Medway Handyman"

He's talking crap anyway - thickwalled plastic water main (and yellow gas pipe) makes a perfectly fine vacuum chamber, if you put a suitable domed end cap onto it. You might suck a flat plate endcap inside out, but you won't collapse a _cylinder_ of this material.

I did try to tell said plonker this...... but he wasn't listening.