4000 psi sounds like a lot. That's what some pressure washers can go up to. Just how much pressure is that? What are some real world examples that would help explain that kind of pressure?
4000 PSI is too much or a shitload of pressure. I would never use it on high on anything that I was cleaning at a home. Even brick work could get damaged of up close 4000 PSI. Probably the only thing I would use it for is cleaning my driveway but even then I would probably use a fan nozzle. 4000 PSI would just rip the paint off a home - one with a really good paint job.
If you want to really clean instead of blasting the crap out of something the key isn't just PSI, it is also a factor of the waterflow rate. This is measured on most powerwashers as GPM or gallons per minute. You multiply GPM and the PSI to get the cleaning units (CUs) of your powerwasher. This is the most important factor for cleaning, not PSI. A lot of the big box stores sell their cheaper powerwashers with high PSI because that is what the consumer is used to looking for. These high PSI, low GPM units will not clean as well and are more likely to damage the surface you're cleaning.
Note: The chart below references usage based on staying an appropriate distance for the material and PSI. Obviously if you just look at the first column and you spray your car with a 2500 PSI powerwasher from point blank, get ready for a new pain job.
Things I have used a powerwasher for:
- decks (be careful with composite)
- non-painted fences
- garage floors
- houses wood (it isn't my first choice or even second. Also if I am painting I need 4-5 days of summer after powerwashing)
- brick (but very risky and must take your time and stand back and properly presoap. You can cut mortar loose)
- my trailers
- greasy tools (non-electric all metal)
Things I try not to powerwash:
- houses (vinyl no way, brick is a risk, even wood I will stand back a bit)
- windows (you will destroy the caulking)
- painted fences
- anything inside
Take a moderately average car, such as a Honda Civic - roughly 3000 lbs (depending on options, year, etc)
Balance it on a US Quarter (0.955 inch diameter, 0.716 square inches)
Stick to quarters. Per US Mint specs, a quarter (at least a new, unworn one) has a mass of 5.67 grams, and so long as we are on Earth that's equivalent to 0.01250021026674 lbs. So a stack of 299,213 quarters (or $57,303.25 in quarters) would exert 4000 PSI.
Wikipedia claims that steel ranges in density from 485-503 lbs/cubic foot. Let's call it 495. there are 12x12x12 cubic inches in a cubic foot, so a cubic inch of steel weighs 0.286458333 lbs.
So a 1 inch square solid bar of steel would be 13,963.64 inches tall to exert 4000 PSI (if you could get it to stand on end) - that's a bit more than 0.22 mile tall.
A 97.6 lb lady wearing high heels that are 5/32" square, balancing on one heel.
As mentioned above, if you could fit two tons on a 1" square, that's what it would be.
Since you mentioned pressure washers, I'll throw in a few other observations. Many electric models will do no more than 2000 PSI. Some gas-engine models can exceed 4,000 PSI. Pressures as low as 1000 PSI can still cause damage or personal injury, so be careful. If you're going to use one for cleaning a deck, siding, or something else around your home, make sure your water system can supply the washer. (And be careful with water if you use an electric pressure washer.)
4000 PSI is exactly how much pressure it is. PSI = Pounds per Square Inch. I'm not really sure what kind of example you are looking for. PSI is a general unit that depends on context to determine if a given value is too much or not enough.
Since you ask for examples though:
- A typical air compressor for powering air tools runs up to 140 PSI.
- Water pressure in your house is about 40-70 PSI.
- Hydraulic cylinders in machinery can operate up to 30,000 PSI or more.
Those are examples of fluids exerting pressure on their container.
But PSI is also used to measure compressive strength. For example:
- "5000 PSI" concrete attains a compressive strength of 1500 PSI after 1 day of curing, 2500 PSI after 3 days of curing, 3500 PSI after 1 week of curing, and 5000 PSI after 28 days of curing.
- Dry maple wood can attain up to 56,000 kPa (8122 PSI) of compressive strength parallel to the grain.
Additional examples that might make it more intuitive to understand from a scuba diving perspective.
Air pressure is commonly measured in bar. Air pressure (at sea level) is about 14.7 PSI or 1 bar. So the pressure exerted by all the air around you is 14.7 pounds per square inch.
As a general rule of thumb the pressure in bars increases by 1 for every 10m that you go under water. So at 10m the pressure is 2 bar, 20 is 3 bar etc.
So to illustrate your question on 4000psi. That would be equivalent to the pressure 2,700m deep in the ocean! So yes that is quite a lot of pressure
Another practical example a typical high pressure home water heater is rated at 6 bar or 88psi or 50 meters of ocean depth. your example of 4000 is 45x greater than water pressure from your high pressure water heater.
I know the question was in regards to pressure washers, but to help visualize the amount of force involved from a human perspective, let's just model the human body roughly as a 2 foot by 6 foot rectangle laying on the ground. That puts your surface area at 24in x 72in = 1728 square inches. If the atmosphere were pushing down on you with 4000 pounds on every one of those 1728 square inches, it would be like a 6,912,000 pound elephant sitting on top of you...
But really, you don't have a feel for the situation until you account for the surface to which the pressure is being applied. For instance, the components of the pressure washer which are exposed to the 4000 psi have a much smaller surface area and thus do not experience near the kind of force in my example above.