It all depends on how you do the pressure washing,I deal with machines ranging from little 1000psi electric all the way up to 10000 psi gas and diesel units at work,most people use the small units found at the local hardware stores.The washers pressure rating is found at the tip of the spray wand.If you were to take a reading directly at the tip it would read for a 1500psi unit 1500psi,if you take the reading at 2ft from the tip it would read around 200 psi or less.DO NOT PUT YOUR HAND DIRECTLY AGAINST THE TIP TO TRY THIS!!!Water injected into the skin is very dangerous and painfull. I believe most people that are having the problem with water getting into bearings and seals is because they have the tip of the wand too close to the bike,back it off and you will not have any problem.I have been pressure washing my bikes for over 15 years and have never had a bearing or seal damaged from pressure washing,the unit I use is a hot water unit putting out 1500 psi ,the key is to keep the wand backed away from the delicate areas.
Not to sound like a salesman but when or if you are looking for a pressure washer pay more attention to the gallons per minute that the machines put out then psi.A 1500psi machine putting out 5 gallons per minute is going to do a better job then a 2000 psi machine putting out 3.5 gallons per minute.In the case of pressure washers it is the volume of water that a machine puts out that does a better job.It washes away the dirt better.
Machines are usually rated in the 500 psi areas eg;1000,1500,2000 and 2500psi, if you see a machine with a 1250 or 1750 psi rating it is usually done by replacing a 1000 or 1500 psi machines tip with the next size down to increase the pressure,but you are actually decreasing the gallons per minute,watch out for this.