Pressure Washer Physics

Scott Stone said:
How many GPM are you looking at? And do you want the size of both pulleys, or do you already have one that you want to use, that you picked up at Harbor Freight?
Click to expand...

I think 1750 rpm is the max I would want to run the pump.

I think that should give me about 6.6 gpm? Right?

It looks like I have a 4 1/2 inch motor pump and a 9 inch pulley pump.

I think that should put me right at around 1725-1750 with load.

Am I right at 6.6 gpm?

Theoretically I could push 2500 psi with a #8.5 nozzle at 6.6 gpm with that pulley combination and the 18 hp motor. Or am I off?
 
18hp x 75% = 13.5hp
13.5 / .0007 / 6.6gpm = 2900psi Maximum !!!

6.6gpm x 2500psi x .0007 = 11.55hp
= your 18hp engine at 65% ... = coooler running reliabilty.. especially in the Las Vegas sun

Note:
DUAL FEED THAT PUMP !!! .. or eat seals and valve seat o-rings FREAKquently.
:{p

Oh wait ! ..you already knew that, from the Troubleshooting and BulletProofing class !
:{)
 
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Sirocco Jerry said:
18hp x 75% = 13.5hp
13.5 / .0007 / 6.6gpm = 2900psi Maximum !!!

6.6gpm x 2500psi x .0007 = 11.55hp
= your 18hp engine at 65% ... = coooler running reliabilty.. especially in the Las Vegas sun

Note:
DUAL FEED THAT PUMP !!! .. or eat seals and valve seat o-rings FREAKquently.
:{p

Oh wait ! ..you already knew that, from the Troubleshooting and BulletProofing class !
:{)
Click to expand...


Jerry, if there is a Tampa event this year, will you be attending? If you will be there, will you be offering the "Bulletproofing Class"? I know I am not the only person that would like to attend that class if it is offered.
 
Tony Shelton said:
I think 1750 rpm is the max I would want to run the pump.

I think that should give me about 6.6 gpm? Right?

It looks like I have a 4 1/2 inch motor pump and a 9 inch pulley pump.

I think that should put me right at around 1725-1750 with load.

Am I right at 6.6 gpm?

Theoretically I could push 2500 psi with a #8.5 nozzle at 6.6 gpm with that pulley combination and the 18 hp motor. Or am I off?
Click to expand...

Sirocco Jerry said:
18hp x 75% = 13.5hp
13.5 / .0007 / 6.6gpm = 2900psi Maximum !!!

6.6gpm x 2500psi x .0007 = 11.55hp
= your 18hp engine at 65% ... = coooler running reliabilty.. especially in the Las Vegas sun

Note:
DUAL FEED THAT PUMP !!! .. or eat seals and valve seat o-rings FREAKquently.
:{p

Oh wait ! ..you already knew that, from the Troubleshooting and BulletProofing class !
:{)
Click to expand...

Keep in mind that the pump is still only a 5.6 pump, and if I remember correctly, that is all the water the pump is supposed to put out.
 
Robert Hinderliter said:
Basic Power Washing Math, hope this helps someone.
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Robert Hinderliter said:
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Thanks Robert for the useful information.
 
With a #6 nozzle I got 3000 psi. I'm assuming that is 6.6 gpm. It feels like it.

Somebody needs to look at their charts again about how much pressure you loose every 100 ft.

With the same gun and nozzle I got 2800 psi at the end of 480ft and through the hose reel.
 
Tony Shelton said:
With a #6 nozzle I got 3000 psi. I'm assuming that is 6.6 gpm. It feels like it.

Somebody needs to look at their charts again about how much pressure you loose every 100 ft.

With the same gun and nozzle I got 2800 psi at the end of 480ft and through the hose reel.
Click to expand...

3000 psi with a #6 shows 5.s gallons.
Flow chart says 100 + psi per 100 feet, interesting
 
Sorry. You are no longer worth talking to. 170 degrees? You cant even melt kevlar with that.
 
tomtucson said:
3000 psi with a #6 shows 5.s gallons.
Flow chart says 100 + psi per 100 feet, interesting
Click to expand...

For the average contractor, figure pressure loss of one (1) psi per foot. Also every 90 degree bend adds quite a bit of pressure loss, look at your hose reels which have several 90 degree bends.

If your down stream injector does not work, move it from the outlet of your pressure washer to the outlet of you hose reel. This is the most common place a contractor has trouble with pressure loss.
 
hose-friction-loss.jpg


Real world seems to be less than calculated. Interesting Tony has 500 ft and 200 psi lost. I would think as a hose ages the inside becomes rougher.
 
tomtucson said:
hose-friction-loss.jpg


Real world seems to be less than calculated. Interesting Tony has 500 ft and 200 psi lost. I would think as a hose ages the inside becomes rougher.
Click to expand...

I was wondering if it was because the hose was still rolled up on the reel and had very little room for expansion.

Sent from my DROID RAZR using Tapatalk 2
 
Maybe there is something with the hot water affecting the pressure, maybe that increase in temperature is causing more pressure in the line so at the end there is less of a loss from internal friction?
 
Scott Stone said:
Keep in mind that the pump is still only a 5.6 pump,
..and if I remember correctly, that is all the water the pump is supposed to put out.
Click to expand...

THese pumps are positive displacement pumps..
if you feed it with "the perfect water supply" .. it will pump the flow you turn it for..
5.6gpm pump at an increase of 20% in rpm will yield an increase of 20% in gpm.
How long the seals and valves last, is another story.
How much the manufacture "commits" for warranteability.. is a simple judgement call in "risk management"

I have been told by 3 pump manufacturers that I can turn their pumps at 10% over the rated speed without a change in warranty.
The same 3 told me I could run'em at 20% over, "with approval", and running at reduced pressure,
so as to NOT overheat the back-end of the pump.


Scott Stone said:
Sorry. You are no longer worth talking to.
.. 170 degrees? You cant even melt kevlar with that.
Click to expand...

Scott, you are one funny guy.
:{)
 
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