Pressure Washer

[Newps]

Got a new pressure washer today and I want to bring it to the airport to
wash the plane. It needs 20 psi to work properly. If I put a 100
gallon water tank in my truck and fed the pressure washer with a
standard 5/8" garden hose and a 3 foot drop to the pressure washer on
the ground would that give me 20 psi?

[nrp]

would that give me 20 psi?

No - You only theoretically get about 0.43 psi per foot of water head -
and that is ignoring the wall friction effects of a 5/8 in hose.

Use auto wash soap and warm water & a rag or sponge. A pressure washer
is hell on bearing seals etc and will promote corrosion in the areas
that get pried open from the wash pressure.

A rainy day also makes a good wash day with a soft water rinse.

[Newps]

nrp wrote:

> would that give me 20 psi?
>
> No - You only theoretically get about 0.43 psi per foot of water head -
> and that is ignoring the wall friction effects of a 5/8 in hose.
>
> Use auto wash soap and warm water & a rag or sponge. A pressure washer
> is hell on bearing seals etc and will promote corrosion in the areas
> that get pried open from the wash pressure.

So what would the pressure be?

[Dave S]

Water pressure is a matter of height/elevation. From my fire department
days, you will get static pressure of 1/2" pound PSI per foot of
elevation.. so you need 10 feet of water to get that 20 psi.

You've got approx 1.5 psi there of head pressure.

Considering you will be flowing very little in the way of gallons per
minute, I wont address the flow related pressure loss in that 5/8" hose.

Chances are you will actually do just fine.. If not, then you need to
"make" a tank that can handle pressure (such as a large air compressor's
tank.. coat it for rust proofing, and put an air nipple on it and charge
it to 20 psi.. which is prolly overkill in my opinion.. people have
pressure washers in the back of trailers all the time with a feed tank
right next to it, running atmospheric pressure feeds.

Dave

Newps wrote:

> Got a new pressure washer today and I want to bring it to the airport to
> wash the plane. It needs 20 psi to work properly. If I put a 100
> gallon water tank in my truck and fed the pressure washer with a
> standard 5/8" garden hose and a 3 foot drop to the pressure washer on
> the ground would that give me 20 psi?

[Mike Rapoport]

"Newps" > wrote in message
...
> Got a new pressure washer today and I want to bring it to the airport to
> wash the plane. It needs 20 psi to work properly. If I put a 100 gallon
> water tank in my truck and fed the pressure washer with a standard 5/8"
> garden hose and a 3 foot drop to the pressure washer on the ground would
> that give me 20 psi?

The answer is no you will not get 20psi. However, I have a 13hp Karcher
pressure washer that I bought at Costco and I have found that you don't need
much pressure to the inlet side for it to work. Try to get the largest
possible hose and fittings. You need an inlet that flows at least as much
as the pressure washer is rated for. The goal is to have enough pressure
that the pump doesn't cavitate. It doesn't take 20psi.

Mike
MU-2

[Newps]

Mike Rapoport wrote:
> "Newps" > wrote in message
> ...
>
>>Got a new pressure washer today and I want to bring it to the airport to
>>wash the plane. It needs 20 psi to work properly. If I put a 100 gallon
>>water tank in my truck and fed the pressure washer with a standard 5/8"
>>garden hose and a 3 foot drop to the pressure washer on the ground would
>>that give me 20 psi?
>
>
> The answer is no you will not get 20psi. However, I have a 13hp Karcher
> pressure washer that I bought at Costco and I have found that you don't need
> much pressure to the inlet side for it to work. Try to get the largest
> possible hose and fittings. You need an inlet that flows at least as much
> as the pressure washer is rated for. The goal is to have enough pressure
> that the pump doesn't cavitate. It doesn't take 20psi.

I can get a bigger hose but the inlet fitting is a standard garden hose
fitting.

[Mike W.]

That's fine. The idea is to get enough water flow from your tank to feed the
pump. Like another poster said, with inadequate water flow it will cavitate
and the sprayer will start burping out air.
The reason they tell you a minimum of 20psi is they figure worst case,
somebody will hook it up with a 1/2" garden hose. So in order for that hose
to deliver water at a useable rate, you need around 20psi.

--
Hello, my name is Mike, and I am an airplane addict....

"Newps" > wrote in message
...
> I can get a bigger hose but the inlet fitting is a standard garden hose
> fitting.

[George Patterson]

Dave S wrote:
> Water pressure is a matter of height/elevation. From my fire department
> days, you will get static pressure of 1/2" pound PSI per foot of
> elevation.. so you need 10 feet of water to get that 20 psi.

Wouldn't that be 40' of elevation to get 20 psi?

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

[Dave S]

Yes.. you are absolutely right.. and someone else earlier gave the more
exact value of 0.4 psi/ft so actually its more like 50 feet. I had the
right idea but did the wrong math the first time around.

Think about it like this.. most water towers are in the 100 ft range to
get spigot pressures of 40-50 psi. Modern practice is now to get away
from towers and stick with continuous duty pumps, but the old style
still persists.

Dave

Thanks.

George Patterson wrote:
> Dave S wrote:
>
>> Water pressure is a matter of height/elevation. From my fire
>> department days, you will get static pressure of 1/2" pound PSI per
>> foot of elevation.. so you need 10 feet of water to get that 20 psi.
>
>
> Wouldn't that be 40' of elevation to get 20 psi?
>
> George Patterson
> There's plenty of room for all of God's creatures. Right next to the
> mashed potatoes.

[Dave S]

Mike W. wrote:

> That's fine. The idea is to get enough water flow from your tank to feed the
> pump. Like another poster said, with inadequate water flow it will cavitate
> and the sprayer will start burping out air.
> The reason they tell you a minimum of 20psi is they figure worst case,
> somebody will hook it up with a 1/2" garden hose. So in order for that hose
> to deliver water at a useable rate, you need around 20psi.
>

Especially if say, you were feeding that flow rate though 100 feet of
1/2" hose. The flow losses are directly related to the distance.

Dave

[Nathan Young]

On Sat, 30 Apr 2005 03:14:38 GMT, Dave S >
wrote:

>Think about it like this.. most water towers are in the 100 ft range to
>get spigot pressures of 40-50 psi. Modern practice is now to get away
>from towers and stick with continuous duty pumps, but the old style
>still persists.

Really? This surprises me. Water towers offer a lot of benefits.

Water towers allow the purchase of smaller pumps, that will serve the
average water flow through the day, vs. peak rate. That saves initial
capital cost.

Water towers are sized to provide a day or so of water to the
community in the event that the pump breaks or power is interrupted.

Last, space on water towers are now leased to cellular carriers, so
the towers actually provide a revenue stream for the city.

OTOH, it probably costs a fair amount of money to build a water tower,
so the capital costs may outweight the benefits. Although for what
the cell carriers pay for leases, I'd be surprised if it didn't cover
the mortgage/bond on the water tower.

[houstondan]

Nathan Young wrote:
((snip))
> Really? This surprises me. Water towers offer a lot of benefits.
>
>
((snip))


american water works assn and most states still consider elevated water
best, ground tank on a hill works fine, but the costs for maintenance,
worker and community issues get pretty rough. the real issues are
firefighting with a dead electric grid and keeping the system
pressurized for health issues. sometimes, if you're clever, you can
get/stay certified with ground storage only by strapping in enough big
deisel generators to keep the pressure up.

personally, i like having lots of water towers with place names on them
as an easy and reasuring answer to the question "where the heck am i??"
although often as not the city name is covered with spray paint
announcing that sally did tommy which isn't much help unless you happen
to know sally. hence the aforementioned maintenance issue.


dan