Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

On 01/04/2012 15:28, Hugo Nebula wrote:

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?

There's certainly no need for them to shift vast volumes of water to be
effective. I think the point is that they generate (or should do) a very
high pressure by pumping water through a very small orifice. Certainly
my Karcher blasts out a very effective jet, but the actual flow rate is
way less than provided by a mains-fed tap.

David

[Default] On Sun, 01 Apr 2012 16:03:42 +0100, a certain chimpanzee,
Lobster , randomly hit the keyboard
and wrote:

There's certainly no need for them to shift vast volumes of water to be
effective. I think the point is that they generate (or should do) a very
high pressure by pumping water through a very small orifice. Certainly
my Karcher blasts out a very effective jet, but the actual flow rate is
way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

In message , Hugo Nebula
writes
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?


They, as the name suggests, provide extra pressure and not flow rate, so
I would expect an open hose to provide a higher flow rate, otherwise
they would be sucking water out of your mains.

I use a middle of the road Karcher and it is marvellous, fetches paving
slabs and concrete back to a nice crisp finish and clears most of the
dirt off the car. If you have it on a pencil jet and it cuts the rubber
trim around the windows then it is OK. A problem I had when I first
used mine years ago. Quite good at taking paint off painted bumpers too
if there are any stone chips.
--
Bill

"Bill" wrote in message
...
In message , Hugo Nebula
writes
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?


They, as the name suggests, provide extra pressure and not flow rate, so I
would expect an open hose to provide a higher flow rate, otherwise they
would be sucking water out of your mains.

I use a middle of the road Karcher and it is marvellous, fetches paving
slabs and concrete back to a nice crisp finish and clears most of the dirt
off the car.

Those are mainly what I use mine for, plus with not-so-great drainage in my
back garden, I can clean it all without flooding the garden because it uses
less water than a hose. The patio looks like new at the moment, I don't
think anything else would bring it up that clean.

I'm assuming the best way to compare tap versus jetwasher is the bar
measurement rather than flow rate. I think my washer is about 120bar, that's
way more than a tap. You can stop a tap running with your thumb over it, you
ain't stopping a jet from these machines.

On Sun, 01 Apr 2012 16:13:06 +0100
Hugo Nebula wrote:

[Default] On Sun, 01 Apr 2012 16:03:42 +0100, a certain chimpanzee,
Lobster , randomly hit the keyboard
and wrote:

There's certainly no need for them to shift vast volumes of water to
be effective. I think the point is that they generate (or should do)
a very high pressure by pumping water through a very small orifice.
Certainly my Karcher blasts out a very effective jet, but the actual
flow rate is way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?

No, because you can't generate more pressure than you start with
without some extra force, such as a pump.
--
Davey.

"Hugo Nebula" wrote in message
...
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

Pressure washers are a positive displacement pump.
They deliver a fixed amount of water.
http://en.wikipedia.org/wiki/Positiv...acement_p ump

The pressure you get depends on how small the outlet orifice is.

So to get a higher pressure you adjust the outlet down.
If the outlet is wide open, you just get a miserable dribble.
(But it is the same volume of water.

There is a relief/bypass valve inside opens if over pressure ocurrs.
eg when the operating valve on the lance is closed.

In article ,
Hugo Nebula writes:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure
can take the paint off.

I do use one for washing the car, but the main purpose is to
pump the water from the water butt. I never point a high pressure
jet straight at the paintwork, or elsewhere where it might cause
damage. I use a soft brush attachment for washing, and a misting
spray for rinsing.

Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

The flow rate from most is quite low.

Am I missing something here? Is pressure a function of the flow rate,

No.

To a first approximation, pressure x flow rate will be proportional
to the power consumption, but that ignores that some have efficient
induction motors, and others apparently have less efficient (and
probably shorter life) universal motors.

and if so, what's the point of a pressure washer if it gives less than
mains pressure?

They are much higher pressure than mains.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 01/04/2012 16:13, Hugo Nebula wrote:
[Default] On Sun, 01 Apr 2012 16:03:42 +0100, a certain chimpanzee,
, randomly hit the keyboard
and wrote:

There's certainly no need for them to shift vast volumes of water to be
effective. I think the point is that they generate (or should do) a very
high pressure by pumping water through a very small orifice. Certainly
my Karcher blasts out a very effective jet, but the actual flow rate is
way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?

There is a limit to the flow rate through a small nozzle unless you
apply a much larger pressure (ie pump) to the back side of it. People
make terrible mistakes with leaking high pressure hydraulics systems.

A small amount of water carrying a large amount of kinetic energy can do
a lot of damage. I would not use one on my car as I don't want to grit
blast the surface or strip the paint. YMMV Fine for use on dirty patios
though and stone doesn't suffer much from additional scratches.

--
Regards,
Martin Brown

On Sun, 01 Apr 2012 15:28:07 +0100, Hugo Nebula wrote:

Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

Road film is remarkably resistant to simply being blasted off. You
still need some form of rubbing to get it off, either a brush or
cloth. If just pressurised water was enough do you think automatic
car washers would have
great big rotating brushes?

http://www.diyfaq.org.uk/electrical/...washer_faq.htm

--
Cheers
Dave.

On 01/04/2012 15:28, Hugo Nebula wrote:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

The dirt on cars is known as 'traffic film' and comprises of unburnt
fuel residue, oil/grease residue, small amount of rubber & general
grime. It's basically oil based & forms an extremely good bond to
vehicle paintwork. In addition, since the vehicle is moving while it
gets dirty, a static bond is also generated.

It short, it's a bugger to remove without mechanical agitation.

Pressurised water alone will not shift traffic film. A specific
detergent - known as a Traffic Film Remover or TFR is needed to remove
it. You won't find a decent product in a DIY place, proper TFR is
pretty nasty stuff - pH of around 13. You need to go to a specialised
pressure washer dealer.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Pressure washers were developed in Denmark & Germany when water & it's
disposal has always been very expensive. The concept was that you could
do the same amount of cleaning with much less water. In the UK, where
water has been cheaper, they were sold as labour saving, not water saving.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?

You are confusing flow & pressure. A household tap may give 5 bar at 15
litres a minute. Connecting a pressure washer to that tap gives say 100
bar at 10 litres/min - which is a tenfold increase in cleaning power.

The balance of pressure/flow is important. 120 bar @ 6.5 l/min is less
powerful than 100 bar @ 8 l/min.

Have a look here;

http://wiki.diyfaq.org.uk/index.php?...ure_washer_FAQ

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

Andrew Gabriel wrote:

Hugo writes:

a pressure washer is needed to wash one's car properly.

Really? I thought a problem with them for this purpose is the
pressure can take the paint off.

Not for blasting the dirt (and paint) off, but for applying the
snow-foam ...

http://youtu.be/RG9djNcu23M

On 01/04/2012 17:41, Andrew Gabriel wrote:
In ,
Hugo writes:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure
can take the paint off.

Urban myth.

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

Hugo Nebula wrote:

Reading car forums, the overwhelming opinion is that a pressure
washer is needed to wash one's car properly. So I went and
bought a cheap Halfords one, complete with snow foam
attachment. The results were disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It amounts
to 1,000 litres per hour, nearly three times the flow rate of the PW. Some
of the best pressure washers only appear to give half of that.

Am I missing something here?

Yep.

Is pressure a function of the flow rate,

Nope.

and if so, what's the point of a pressure washer if it gives less than mains pressure?

It doesnt with a decent one.

Hugo Nebula wrote
Lobster wrote

There's certainly no need for them to shift vast volumes of water
to be effective. I think the point is that they generate (or should do)
a very high pressure by pumping water through a very small orifice.
Certainly my Karcher blasts out a very effective jet, but the actual
flow rate is way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?

Nope, the pressure is much lower than with a decent pressure washer.

In message , The Medway Handyman
writes
On 01/04/2012 17:41, Andrew Gabriel wrote:
In ,
Hugo writes:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure
can take the paint off.

Urban myth.

Tell that to the painted plastic bumper on a Mondeo I had! :-)

There again it didn't harm the painted metalwork.


--
Bill

Bill wrote:

The Medway Handyman writes

On 01/04/2012 17:41, Andrew Gabriel wrote:

I thought a problem with them for this purpose is the pressure
can take the paint off.

Urban myth.

Tell that to the painted plastic bumper on a Mondeo I had!

Ditto bumper on an old car of mine.

The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.

On 01/04/2012 19:08, Rod Speed wrote:
The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.


I sold pressure washers for 30 odd years. I only know of on instance of
paint removal & that was a Lada the owner had hand painted.

'If' a pressure washer takes paint off - the paint was coming off anyway
- the pressure washer just brought the date forward.

--
Dave - The Medway Handyman www.medwayhandyman.co.uk

The Medway Handyman wrote
Rod Speed wrote
The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.

I sold pressure washers for 30 odd years. I only know of on instance
of paint removal & that was a Lada the owner had hand painted.

Irrelevant to what others have seen.

'If' a pressure washer takes paint off - the paint was coming off
anyway - the pressure washer just brought the date forward.

That is just plain wrong with the motorbike I was talking about.

On Sun, 01 Apr 2012 19:13:17 +0100, The Medway Handyman
wrote:

On 01/04/2012 19:08, Rod Speed wrote:
The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.


I sold pressure washers for 30 odd years. I only know of on instance of
paint removal & that was a Lada the owner had hand painted.

'If' a pressure washer takes paint off - the paint was coming off anyway
- the pressure washer just brought the date forward.

Well my wheel-nut covers were fine before they washed my car after
servicing it last time. Perhaps they used an angle grinder and not a
PW? And no Skoda jokes Mr Lang!
http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

Funnily enough, it's going in for a service in the morning so I will
remember now to tell them not to bother washing it.
What should I use to spray the plastic covers with?

--
Graham.
%Profound_observation%

On Sun, 1 Apr 2012 16:41:32 +0000 (UTC),
(Andrew Gabriel) wrote:

I thought a problem with them for this purpose is the pressure
can take the paint off.

Only time I've ever done that was when the paint was pretty ****tily
applied in the first place and deserved to come off. In fact, it was
waiting for the first heavy rain to take it off.

On Sun, 01 Apr 2012 19:51:44 +0100, Graham. wrote:

Well my wheel-nut covers were fine before they washed my car after
servicing it last time. Perhaps they used an angle grinder and not a
PW? And no Skoda jokes Mr Lang!
http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

How to tell if the previous owner or dealer hadn't tarted them up with
a pot of paint?

Hugo Nebula wrote:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?

I believe they were invented as a water SAVING device. They don't use
much water but should produce a high pressure jet. Mine certainly does.

Is there a leak at the junction of the wand and the machine?

Another Dave

--
Change nospam to gmx

On Sun, 01 Apr 2012 17:54:00 +0100 (BST), "Dave Liquorice"
wrote:

Road film is remarkably resistant to simply being blasted off. You
still need some form of rubbing to get it off, either a brush or
cloth. If just pressurised water was enough do you think automatic
car washers would have
great big rotating brushes?

Traffic Film Remover - the real stuff, not the weak as **** stiff in
Halforts, is really good at that.

On Sun, 01 Apr 2012 20:24:00 +0100, wrote:

On Sun, 01 Apr 2012 19:51:44 +0100, Graham. wrote:

Well my wheel-nut covers were fine before they washed my car after
servicing it last time. Perhaps they used an angle grinder and not a
PW? And no Skoda jokes Mr Lang!
http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

How to tell if the previous owner or dealer hadn't tarted them up with
a pot of paint?

It's a leased company vehicle, but it was new when I got it, so that's
unlikely.

--
Graham.
%Profound_observation%

In message , Graham.
wrote

Well my wheel-nut covers were fine before they washed my car after
servicing it last time. Perhaps they used an angle grinder and not a
PW? And no Skoda jokes Mr Lang!
http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

I'll bet that they sprayed the wheels with a fairly aggressive acid or
alkali wheel cleaner before pressure washing and that is what has
damaged the finished surface on the nuts.

My local car wash starts with spraying a solution on the wheels using a
hard "garden pump up sprayer" followed by lather socked brush to remove
bugs and bird ****, followed by a quick pressure washer around the
wheels and windscreen, followed by the trip through the rotating
knives[1].

[1]
http://www.youtube.com/watch?v=e2PyeXRwhCE

--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

In article ,
The Medway Handyman writes:
On 01/04/2012 19:08, Rod Speed wrote:
The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.


I sold pressure washers for 30 odd years. I only know of on instance of
paint removal & that was a Lada the owner had hand painted.

'If' a pressure washer takes paint off - the paint was coming off anyway
- the pressure washer just brought the date forward.

The water based paints they have to use today don't stick
as well as the solvent based paints which used to be used.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In message , Andrew Gabriel
wrote

The water based paints they have to use today don't stick
as well as the solvent based paints which used to be used.



That's why you shouldn't drive too fast in the rain.
--
Alan
news2009 {at} admac {dot} myzen {dot} co {dot} uk

On Sun, 01 Apr 2012 19:03:36 +0100, Andy Burns wrote:

I thought a problem with them for this purpose is the pressure
can take the paint off.

Urban myth.

Tell that to the painted plastic bumper on a Mondeo I had!

Ditto bumper on an old car of mine.

Yep I know of two people who have stripped paint off their plastic
bumpers first outing with a new PW. Pencil jet and tyres aren't
supposed to be a good combination either.

--
Cheers
Dave.

On 01/04/2012 20:24, Another Dave wrote:
Hugo Nebula wrote:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?

I believe they were invented as a water SAVING device. They don't use
much water but should produce a high pressure jet. Mine certainly does.

Is there a leak at the junction of the wand and the machine?

Another Dave

Ok a non tech answer :-)
And I dont recommend this.
I have a cheap one but was more than happy with the patio results to the
point I got carried away and decided to clean the plastic patio
table....It now has grooves cut into the table top where I used the PW,
this wouldnt have happened with a garden hose, I could have ripped
through it given a few more minutes.
Last year in hot weather (bare feet) cleaning the slabs.... I accidently
blasted my foot with the jet....damn painful it was, again much more
pressure than a garden hose.
In both instances it used much less water than a hose.

On 01/04/2012 15:28, Hugo Nebula wrote:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here?

YES!

A pressure washer blasts a relatively small amount of water through a
small nozzle at very high *velocity* - thus imparting a very high force
on any surface impacted by the jet. This is great for cleaning patios
etc. (been using one myself, today!). Many lances have adjustable
nozzles - so you can have a very narrow very fast jet, or a wider 'fan'
at lower velocity. The wider fan is much faster, but you sometimes need
to reduce the size of the jet to remove very stubborn dirt.

When washing cars with a foaming device, the water is usually delivered
through a brush or a fairly wide nozzle, so far less back pressure is
produced. That's really a two stage operation: Stage 1 to spread the
foam and loosen the dirt, and Stage 2 to blast the loosened dirt off
with a small-bore high pressure nozzle.

I wouldn't bother with a pressure washer for washing cars - a bucket of
soapy water applied with a hand-brush, and then washed off with a garden
hose, is just as good. But patios are a different matter!
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

In message , Bill
writes
In message , Hugo Nebula
writes
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?


They, as the name suggests, provide extra pressure and not flow rate,
so I would expect an open hose to provide a higher flow rate, otherwise
they would be sucking water out of your mains.

I use a middle of the road Karcher and it is marvellous, fetches
paving slabs and concrete back to a nice crisp finish and clears most
of the dirt off the car. If you have it on a pencil jet and it cuts
the rubber trim around the windows then it is OK. A problem I had when
I first used mine years ago. Quite good at taking paint off painted
bumpers too if there are any stone chips.
A decent lance will have variable pressure. Find they are good for
removing first cover of grime, which is what can scratch with
conventional washing and they are good for final rinsing,, but I still
use bucket and shampoo in between. I fond the detergent adding facility
expensive and a cwt.
--
hugh

In message , Graham.
writes
On Sun, 01 Apr 2012 19:13:17 +0100, The Medway Handyman
wrote:

On 01/04/2012 19:08, Rod Speed wrote:
The Medway Handyman wrote
Andrew Gabriel wrote
Hugo wrote

Reading car forums, the overwhelming opinion is that a pressure
washer is needed to wash one's car properly. So I
went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure can
take the paint off.

Urban myth.

Nope, fact, at least with motorbikes.


I sold pressure washers for 30 odd years. I only know of on instance of
paint removal & that was a Lada the owner had hand painted.

'If' a pressure washer takes paint off - the paint was coming off anyway
- the pressure washer just brought the date forward.

Well my wheel-nut covers were fine before they washed my car after
servicing it last time. Perhaps they used an angle grinder and not a
PW? And no Skoda jokes Mr Lang!
http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

Funnily enough, it's going in for a service in the morning so I will
remember now to tell them not to bother washing it.
What should I use to spray the plastic covers with?

Peugeot dealer wanted to pressure wash my motor caravan when I took it
in for service. Polite but firm No Thank You. I did explain why but I
bet they are still doing it.
--
hugh

On Sun, 01 Apr 2012 20:35:14 +0100, Graham. wrote:

http://www.flickr.com/photos/g3zvt/6...ream/lightbox/

How to tell if the previous owner or dealer hadn't tarted them up with
a pot of paint?

It's a leased company vehicle, but it was new when I got it, so that's
unlikely.

On second look, as Alan says, that's typical of an application of TFR
or somesuch that's been left on too long or is too strong a dilution.

Hugo Nebula wrote:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

flow rate is not pressure.


Am I missing something here?

yes.

Is pressure a function of the flow rate,

No.

and if so, what's the point of a pressure washer if it gives less than
mains pressure?

since it isn't so, think again.


--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.

Hugo Nebula wrote:
[Default] On Sun, 01 Apr 2012 16:03:42 +0100, a certain chimpanzee,
Lobster , randomly hit the keyboard
and wrote:

There's certainly no need for them to shift vast volumes of water to be
effective. I think the point is that they generate (or should do) a very
high pressure by pumping water through a very small orifice. Certainly
my Karcher blasts out a very effective jet, but the actual flow rate is
way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?

No.

--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.

Martin Brown wrote:
On 01/04/2012 16:13, Hugo Nebula wrote:
[Default] On Sun, 01 Apr 2012 16:03:42 +0100, a certain chimpanzee,
, randomly hit the keyboard
and wrote:

There's certainly no need for them to shift vast volumes of water to be
effective. I think the point is that they generate (or should do) a very
high pressure by pumping water through a very small orifice. Certainly
my Karcher blasts out a very effective jet, but the actual flow rate is
way less than provided by a mains-fed tap.

So would a hose with a small nozzle not achieve the same effect?

There is a limit to the flow rate through a small nozzle unless you
apply a much larger pressure (ie pump) to the back side of it. People
make terrible mistakes with leaking high pressure hydraulics systems.

A small amount of water carrying a large amount of kinetic energy can do
a lot of damage. I would not use one on my car as I don't want to grit
blast the surface or strip the paint. YMMV Fine for use on dirty patios
though and stone doesn't suffer much from additional scratches.

That's why you vary the distance to the target and the nozzle dimensions.

They are not sandblasters.


--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.

Bill wrote:
In message , Hugo Nebula
writes
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap
Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?


They, as the name suggests, provide extra pressure and not flow rate, so
I would expect an open hose to provide a higher flow rate, otherwise
they would be sucking water out of your mains.

I use a middle of the road Karcher and it is marvellous, fetches paving
slabs and concrete back to a nice crisp finish and clears most of the
dirt off the car. If you have it on a pencil jet and it cuts the rubber
trim around the windows then it is OK. A problem I had when I first
used mine years ago. Quite good at taking paint off painted bumpers too
if there are any stone chips.

add in getting winter lichen off the garden furniture..not bad at house
paintwork and the windows, too.



--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.

The Medway Handyman wrote:
On 01/04/2012 17:41, Andrew Gabriel wrote:
In ,
Hugo writes:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure
can take the paint off.

Urban myth.

Not a myth, because I have done it: If the paint is already loose they
will take it off, but they wont take paint off a car at the sort of
pressures and distances you normally use a toy one at.

A high pressure industrial jet jet will cut through steel plate...its
all a question of muscle.

http://www.youtube.com/watch?v=bW10fOVIozE


--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.