Trash pump to garden hose to 4200 psi pressure washer

I need to move some water from a river 300 feet to my cabin to do some pressure washing …. I have a 4200 psi Simpson pressure washer ….. I have 300 foot of garden hose. What size water pump/or semi trash pump do I need to make this happen so that pressure washer get enough water…. Is a 1 inch sufficient or a 2 inch …. I’m unsure if there is enough pressure from the output side of the pump when spanning 300 feet …. There is no incline …. Pretty much level all the way …. If I used a 2 inch semi trash pump then reducer coupling down to a 5/8 inch to attach the garden hose seems it would create more pressure and increase gPM to the pressure washer? Or would a simple 1 inch water pump be all I need… I would use an inline screen in the line for any debris if I use just a 1 inch water pump … but pretty much the river water is clean with exception of grasses… any ideas on the project or am I over thinking this

Hi Ben, and welcome to permies. Diameter of hose or pipe is critical to pumping efficiency because of friction with the walls of the pipe. As the diameter gets smaller, the cross sectional area of fluid that travels more or less unimpeded (laminar flow) decreases relative to the edge where there's lots of turbulence. The thickness of the turbulence stays roughly constant for a given speed of fluid movement, so as you shrink the hose, at some point you lose the laminar flow entirely. This really cuts the flow and puts back pressure on the pump.

Length matters as well. A trash pump will be rated for a given length of hose (across level ground) that's the same diameter as its outlet. Longer (or uphill) runs have more friction loss, so you won't be able to pump as far. To make the whole thing work, the best bet is to use the biggest hose you can to get the river water to the inlet of the pressure washer, since it's designed to push into small hose at high pressure.

Here are some examples from my Ace Hardware pocket reference tables on friction loss per 100 feet of pipe:

Pipe diameter	2"	1"	3/4"	1/2"
1 GPM	0	0.5	2.2	15.9
2 GPM	0.1	2	7.9	57.2
5 GPM	0.4	10.7	43.3	*
10 GPM	1.3	38.4	*	*
20 GPM	4.7	*	*	*

* don't bother - you'll blow up your pump

The values in the table get multiplied by a constant for the assumed friction of the interior surface of the hose or pipe and the result is how much static head is lost. New, clean hose might have a value of 120, and after a lot of use this would be around 100.

Offhand, I'm not sure about pushing raw water into a high pressure pump. Regardless of strainers, any entrained fine silt could be extremely abrasive inside the piston chambers. Personally I would be cautious. My 2c.

Yeah, that's a good point too. Maybe pump the river water into one or two IBC totes, let them settle for a day, and then let the pressure washer draw from those.

A settling tank seems a good idea -- more opportunities to filter the water. It depends on the pressure washer though. Some can draw from a tank; others require water pressure at the inlet.

Well I guess I’ll have to rethink k this one…. I do have a 275 gallon tote I could use … or hire someone who does pressure washing that has a on borage tank … thank so much for the help

Settle the water to remove fine abrasives is important.  I would have suggested a plastic liner in something that created walls be it a fort of firewood roped together or a temporary dirt pond with liner.  I am guessing you probably need more on the order of 48+ hours to settle.

Nearly all pressure washers require at least minor pressure to run so you will need to pump out of your storage too.

From experience I know the 5 micron houshold filters(finest commonly available in household filters) still put cloudy water thru and that a filter press at 0.5 micron will take muck and produce clear water from it.  So the dividing line is somewhere in between those 2 numbers.

Now as for the rest you left out two really important number and the first is the amount of head you are lifting.  Is that 300 feet nearly horizontal or is that nearly 300 feet straight up a cliff.  The second is gallons per minute flow for your pressure washer.  At that pressure have seen everything from 1.5 gpm thru 8.? gpm.  What I can tell you is that my pressure washer at the shop is about 350 feet away in 3/4 black poly and up over a hill and back to roughly level with the reservior surface and it keeps up with my 2.5 gpm pressure washer although just barely.  The line is pressurized by a little 1/2 hp irrigation pump.

You could run some river water through a coffee filter and see what you get.

Contacting the manufacturer may also be helpful re the use of raw water.

The 300 foot it pretty much level….. river water is pretty clean ….im just going to have to rethink this

Use the pump to fill the tote.
Have the tote sitting on something to elevate it above the pressure washer.
Let settle if necessary and pressure wash from the tote.
If needed,( I doubt it)  a small electric pump could supply  extra pressure for the washer.