Pressure washers constant pressure

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Discussion Overview

The discussion revolves around the behavior of pressure washers, specifically whether the back-pressure felt when holding a pressure wand increases as one gets closer to a solid surface, such as a wall. Participants explore the implications of nozzle distance on pressure perception, the mechanics of water flow, and the effects of blocking the nozzle.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant argues that the pressure felt is constant and only depends on the set psi of the pressure washer, regardless of distance to the wall.
  • Another participant believes that the back-pressure increases as the nozzle is brought closer to a wall, suggesting that the interaction with the wall affects the pressure felt.
  • A participant questions how close "close" is, indicating that the distance from the wall may influence the flow and pressure dynamics.
  • Concerns are raised about the potential for pressure buildup if the nozzle is blocked, emphasizing the need to turn off the pressure washer in such cases.
  • One participant suggests that there may be no noticeable effect on pressure until very close to the wall, speculating that water may begin to bounce off the wall and affect the flow before any significant pressure change occurs.
  • A more technical contribution calculates the relationship between the distance from the wall and the reaction force experienced, suggesting that a detectable reaction may occur at specific distances.

Areas of Agreement / Disagreement

Participants express differing views on whether the back-pressure increases with proximity to a wall. There is no consensus on the mechanics involved or the specific distances at which changes may occur.

Contextual Notes

Participants note the complexity of the calculations involved in determining pressure dynamics and the influence of distance on water flow, indicating that assumptions about flow behavior may vary.

Spiralout
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My GF and I got into a petty argument about pressure washers. She believes that the constant back-pressure you feel holding a pressure wand increases the closer you hold it to a wall (for example). Where as I believe that if the wand had a constant psi, with outward pressure, wanting to force your arms back while holding it, it would make no difference how close you held it to the wall. I believe that the set pressure coming out would be the only pressure you would feel. She believes the pressure would increase the closer you held the nozzle to a solid surface. Can anyone squash this bug for us?? Irritated boyfriend (who hopes he's not wrong)
 
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Spiralout said:
My GF and I got into a petty argument about pressure washers. She believes that the constant back-pressure you feel holding a pressure wand increases the closer you hold it to a wall (for example). Where as I believe that if the wand had a constant psi, with outward pressure, wanting to force your arms back while holding it, it would make no difference how close you held it to the wall. I believe that the set pressure coming out would be the only pressure you would feel. She believes the pressure would increase the closer you held the nozzle to a solid surface. Can anyone squash this bug for us?? Irritated boyfriend (who hopes he's not wrong)

Try googling Ground Effect...
 
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Thanks for the reply, but I'm not sure if that helps? Couldnt find anything other than aerodynamics of plane wings basically??
 
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Again I am looking for the answer: will the pressure that is forcing my arms back, increase, the closer i hold the pressure washer to a wall. Not, will the wall feel more pressure the closer I hold the pressure washer. Which obviously is yes, it would.
 
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How close is close?

Are pressure washers constant pressure (even when blocked)?
 
If you blocked the opening then pressure could build up and blow a hose. You always have to turn off the pressure. Anyway, I guess nobody knows. Maybe I asked it wrong. Whatever.
 
CWatters said:
How close is close?

Are pressure washers constant pressure (even when blocked)?
Close is say, an inch from the wall
 
I doubt there is any effect until you are very close to the wall. How close is tricky to say. At what point would the flow of water be affected?I wouldn't expect an effect at 1 inch. At some point water is going to bounce off the wall and start hitting the area surrounding the nozzle. I suspect that might happen before any effect due to the flow of water being blocked or slowed.
 
You will start to get increased reaction back into jet when annular flow area between jet and wall becomes of the same order as jet area .

So for a 10mm dia jet :

Area = 10 * 10 * .0.7854 = 78 mm^2

If h is the stand off distance between jet and wall :

Annulus area = 10 * 3.142 * h = 31 * h

h = 78/31 = 2.5 mm

Exact calculation is a bit more complex but expect some detectable reaction from h = 10mm . Reaction will increase as h decreases and there should be a marked increase in reaction for h = 2,5 mm and values down to zero .
 

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