Pressure washers, how do they work?

[busastars]

Realy stupid question Not like me is it to ask stupid questions

Ive taken the handle off my JCB pressure washers expecting to see some kind of cable going to a switch, BUT nope just seems to be a ball bearing that lifts when the triger is pressed.

Reason I ask is because I want to use my pressure washers to have a go at Hydroforming some tube/pipes. I carnt work out if it will work or not as I dont understand how the pressure washers works because I would need quite high preasure.

 

[madkayaker]

there is a pressure switch in the unit that cuts out when its up to pressure

 

[rtbcomp]

Mine had an on/off switch to control the motor, the motor rotated a crinkly plate (swash plate?) which in turn operated three pumps.

There was a relief valve between the inlets and outlets of the pumps and the trigger on the lance just cut off the water to the jet.

With the trigger valve closed water just went round in a circle from outlet to inlet via the relief valve, opening the trigger valve the water took the path of least resistance throgh the nozzle

 

[busastars]

So will I encounter any problems with attaching the hose before the lance to a Hydralic fitting to do some hydroforming.

I know ill probably have to use the on/off switch to control it and also the pressure washers will probably fail in time (its only an old one I have no problem if it goes belly up)

 

[madkayaker]

i managed to snap a fitting on an extension house so decided to use it for cleaning drains. i found i get better flow with the pump off than i do with pump on

 

[rtbcomp]

So will I encounter any problems with attaching the hose before the lance to a Hydralic fitting to do some hydroforming.

I know ill probably have to use the on/off switch to control it and also the pressure washers will probably fail in time (its only an old one I have no problem if it goes belly up)

I don't see any problems.

 

[shenion]

Mine does odd things, you can disconnect the wand and water just dribbles out. It cuts down the pressure if the wand is closed off.

When you pull the trigger, it comes out slow and then builds up pressure.

These have pressure relief valves to protect the pump from overheating. Mine is gas though, so needs the protection.

The electric one I had was similar, the motor ran all the time but it changes speeds depending on the back pressure and the flow. If you adjusted the nozzle for high pressure (more backpressure) the motor kicked up to a higher speed.

 

[busastars]

Mine is just a cheap JCB preasure washer, it seems to be running all the time but as you pull the trigger it kicks into gear.

Im gessing with the chamber that it will slowly fill but motor will kick into action the more the preasure builds up.

Now I need to figure out hydralic conections/fittings for different sizes. Get ready for some more stupid questions reguarding them

 

[pedrobedro]

On mine the back pressure operates a switch inside the unit when you let go of the trigger and the motor cuts out. When you press the trigger the pressure drops and the motor kicks back in

 

[busastars]

Right back to stupid question time


Hydraulic fittings:

Ive just measured the outside thread on the lance, its 14mm. Here is a photo of the fitting:

What type of hydraulic fitting would I need?

Also at the other end I will be using a garden brass tap, dont know the size but will need a hydraulic fitting for that aswell.

Got to be steel as I will need to weld the other end of the hydraulic fitting to a steel pipe/tube.


Probably realy easy thing and take someone 2 seconds to drop me a link to what I need but I have never touched them so havent a clue what is what or if ill even buy the right thing.

Chears

 

[busastars]

I wont edit the above post but digging through my box of bits ive found:

14mm Compressor tool fitting,this is steel and fits

Also found a Washing Machine tap, like the ones that go on the wall. It has aproximatly 26mm thread one side and 20.5mm the other side. I checked with a magnet and its not steel, looks to be brass but chromed, can I get a steel fitting for this????

 

[Dune]

Mine does odd things, you can disconnect the wand and water just dribbles out. It cuts down the pressure if the wand is closed off.

When you pull the trigger, it comes out slow and then builds up pressure.

These have pressure relief valves to protect the pump from overheating. Mine is gas though, so needs the protection.

The electric one I had was similar, the motor ran all the time but it changes speeds depending on the back pressure and the flow. If you adjusted the nozzle for high pressure (more backpressure) the motor kicked up to a higher speed.

The equation that controls the flow is Q=VxA. So Q = discharge V velocity and A is the cross section of the hole or pipe. If you reduce the exit hole the velocity will increase so your discharge can remain constant. Now with a cheap pressure washer the pumps are only there to keep the initial head within the pipeline. The water pipeline in this country is controled to keep the pressure low as its stops pipes bursting etc. and reduces pipe hammer in the system. Pipe hammer in large systems like the water network can be disasterous, pipe exploding pumpng stations being destroyed. So when it comes to turning off a tap the discharge is controlled and the pressure kept constant (to a certain degree). So back to the pressure washer, as the hole on the pressure washer is very small you need to keep the water moving through the system to create the high pressure at the nozzle.

Hope this helps to explain.

 

[pidgeon chit welder]

I think I'm correct in saying ...Remember that you only get the pressure when the nozzle is fitted and forcing water through the jet ..so working back from the spray jet hole size go to the bore of the pump and flow rate to get an idea of what pressures you can expect within your hydro forming jig as you start to get it pumped up to max pressure .

Be careful though for If I'm wrong in what I've said you could be pushing 12,000 to 24,000 psi depending on machine capability over a large surface area of the jig and likely to get a very dangerous explosive leak unless it is massively strong.

 

[busastars]

Thats all good.

Ill have a good old play BUT before I do I just need help with the tap end.

I have this tap, it has aproximatly 26mm thread one side and 20.5mm the other side. I checked with a magnet and its not steel, looks to be brass but chromed, can I get a steel fitting for this?

Would I be better of getting a brass outside tap and getting a steel hydraulic fitting for this? If so can someone recumend one please.

 

[Angusdog]

Be careful though for If I'm wrong in what I've said you could be pushing 12,000 to 24,000 psi depending on machine capability over a large surface area of the jig and likely to get a very dangerous explosive leak unless it is massively strong.

I'm no expert, but since water doesn't compress there is no explosive effect if the vessel ruptures which is why hyroforming is a neat way of making complex organic shapes. I'm thinking of the lickable 2 stroke expansion chambers on GP bikes, mmmmmm

Anyway, we had a hydraulic pump in the welding class that tested our welded vessels (made from tigging cubes from squares of steel) and pumped them up until they ruptured. From memory, mine got to 21,000psi before it leaked, and when it did it was nothing more than a thin squirt of water less than 1mm in diameter, so it's not at all dangerous. Unlike gas under pressure which is. Obviously.

Anyway, I doubt a pressure washer would generate the PSI needed to deform steel, but I would be very happily surprised if it did - for a back yard bodger like me, it sounds like a lot of fun. You make it work and I'll copy you. In other words, you be a western inventor and I'll be China

 

[busastars]

Angusdog, take a quick look at this on youtube:

http://www.youtube.com/watch?v=I_Z3AIFSd60

I know a few people who build there expansion chambers just like this, still im doing my best to get all the bits together.

Just need to sort the tap out (someone throw me a bone here please
Ill be having a go now within two weeks

 

[Angusdog]

Far out - I stand corrected said the man in orthopedic shoes! The thing about this method (as we learnt in welding class) is it requires performance welding and not just sticking metal together, which was why we did it. The neat thing is if it leaks, you can just go over it with the TIG and pump it again. In the vid, it looks like it needs another go to get the wrinkles out, but the method works obviously. I've got a 2 stroke pressure washer, so I'm going to be thinking of all sorts of projects now that use this method. It would be great for sculpture.

 

[busastars]

Still anyone else intrested here is a good write up on doing Hydroforming:

http://www.gifford.ca/hydroform.html

Also Mick Abbey (top UK tunner)

http://www.two-stroke-addicts.freeserve.co.uk/mick/home.htm

I will post up a full write up....... Just need Tap help before I can start, sure someone will tell me.

 

[Dune]

I'm no expert, but since water doesn't compress there is no explosive effect if the vessel ruptures which is why hyroforming is a neat way of making complex organic shapes. I'm thinking of the lickable 2 stroke expansion chambers on GP bikes, mmmmmm

Your right water doesnt compress, the gases entrained in the liquid does. Thats why you can get explosions with compressed water

 

[Master-of-none]

Garden taps are normally 3/4" BSP
It would probably be more controllable to use a hand operated hydraulic test pump rather than a jet wash, especially if the jet wash has a pressure/flow shutdown.