Power washer principle

Does a power washer have to have pressurized water on the inlet, or will it draw from a tank source?
Steve

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On Mon, 20 Sep 2010 07:32:29 -0700, "Steve B"

Most will draw from a tank, many older models do.
The big issue is making sure they get primed. Hence the tank needs to be a bit higher than the pump.
Gunner
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Gunner Asch wrote:

A tank source higher than the pressure washer pump *is* a pressurized source.
Most pressure washer pumps will not give you any reliable suction lift, and can be damaged if they cavitate / run dry. As a general rule, if you want to use water from a pond or the like, you will need to use a second "charge" pump to get the water from the pond to the pressure washer. A filter is also a good idea.
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wrote:

True but most folks dont consider .5psi to be "pressurized" but your meaning is true indeed.

Very true.
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wrote:

IIRC ...................
Salt water is .445 psi per foot of head. Fresh water is .443 per foot of head.
1atm of air at sea level is 14.7 psi, not taking into account barometric pressure variations.
At 33' of diving depth in salt water, it is 14.685 plus the 14.7, making it very nearly 2 atmospheres, or 29.4 psi.
If you are using a gravity feed, the water source would have to be 57.11060948 feet higher than the power washer to provide 40 psig to the washer, and that is allowing for the 14.7 psi for normal atmospheric pressure.
So, it could actually be done with a water source about 60' higher than the power washer.
I was just unsure if the power washer had any suction capabilities, or needed a positive pressure feed. At those conversion factors, and allowing 14.7 psi for sea level pressure, it would take another 25.3 psi to just keep up with it.
Or am I miscalculating, and it would take the full 40 psi?
Steve
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On Mon, 20 Sep 2010 22:03:02 -0700, "Steve B"

It simply needs to have water available for the suction side to be able to pick up. Like from a tank mounted next to and feeding the pump.
Its not rocket science..its simply a pump that has some suction. GPM on the average high pressure pump is quite low, hence they really dont need a lot of water to spray properly.

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wrote:

As is so often the case, you don't have a clue. Some pressure washers such as the CAT models that used an intake tank should be OK with modest suction lift. But most modern consumer-grade models probably aren't. Both of mine will fail to leave unloaded-mode if the pressure intake is restricted very much. Which is probably one of the reasons that most owner's manuals I've seen specifically warn against going below about 20 psi on the intake side. But what do they know compared to the Taft oracle?

Oh really? One of mine is the popular 13hp 4.5 gpm types. Why don't you show us how to calculate the suction specs for that?
Ever thought of not commenting when you when you haven't anything useful to say? Of course not.
Wayne
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What's that Lassie? You say that Steve B fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Mon, 20 Sep 2010 22:03:02 -0700:

Do you need 40psi? Is that what the pump mfg. says, or is that what you have from the garden hose?
I would think that as long as you don't suck air, or cavitate, you could be at 0 psi.
--

Dan H.
northshore MA.
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Gunner Asch wrote:

We've used a cheapie bulge pump and car battery to provide
We've used a cheapie bulge pump and car battery to provide lake water to the pressure washer.
But the washer won't pull water up very far by itself...
--

Richard Lamb



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wrote:

I have a 12v. ShurFlo RV pump that I use to move water around. Would that help any at all?
Steve
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As long as it supplies the max GPM of the washer. JR Dweller in the cellar
On Mon, 20 Sep 2010 21:51:34 -0700, "Steve B"

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On Mon, 20 Sep 2010 21:59:01 -0700, JR North

Or the tank supplies the max GPM of the washer and the pump can fill it back up between sprays.

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On Mon, 20 Sep 2010 07:32:29 -0700, "Steve B"

My pressure washer has a little tank with a float valve that is filled from from a garden hose supply. The washer draws water out of this little tank. If i got a longer pickup tube i could just drop it in a large tank of clean water.
Karl
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Maybe, but it is dangerous for the high pressure pump. It is a general rule of thumb that ALL high pressure pumps be fed by a low pressure supply slightly greater in volume than the max capacity of the high pressure pump to prevent damaging cavitations at the high pressure pump inlet. Steve

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