The jetwash debate (pressure washer),
When my pedal decided to die on sunday (10k up an 11k climb, just before the sweeeeet downhill) and end my ride, the guys who were with me immediately insisted that it was because I use a pressure washer to clean my bike after a ride.
This myth about pressure washers destroying.... er... pedals and stuff is starting to bug me. Does a jet of water really get into bearings and destroy them? No seriously I would love to know for sure one way or the other. Obviously you would have to be pretty dumb to shove the nozzle into a fork seal or bearing dust cap and blast away so discount any of that.
My company has about 50 bikes and we use a pressure washer to clean them, its really the only way to do it without employing half of the Philippines, bikes are tricky to get clean, its complicated and tedious. I do sometimes wonder, when something breaks on one of them; is it because we use a pressure washer?
My pedal is two years old, had a lot of time in rivers, covered in mud and silt and done quite a few miles, is it at all possible that the pressure washer had bugger-all to do with its demise?
I stand to be corrected, at your service, let me know the results of your research, or the considered opinion of a respected professional (I am afraid that since I know several MTB journalists I do not consider their sayings as particularly sooth).
My ceramic bottom bracket is fine, not a hint of a grind or wobble but when it eventually goes, as will all the moving components on my bike since I am too tight to replace them out of vanity, I have little doubt that someone will utter the words "thats what happens when you use a pressure washer" with a knowing grimace (and probably a maid that cleans his / her bike).
Its not a rant, more of a rail against nonsensical mountain biking mythology. It is human nature to hear something and simply believe it because it sounds like it might be plausible, the problem is that it then gets repeated and repeated like an old piece of wisdom passed down through the ages like 'dont lick your razor' or 'wear trousers in the snow'
Off to get some new pedals tomorrow then.....
Subscribe to:
Post Comments (Atom)
I'm a mechanical engineer and a keen MTB / Touring rider. I know a bit about bearings and pressure washers for that matter. It is possible that the pressure washer had nothing to do with your failure but pressure washers are a bad idea on stuff with unsealed bearings on them, this is not myth.
ReplyDeletePressure washers generally have a hose pressure starting from 100 bar to 200 bar but some go up to 3000 bar (3000 bar will take the paint off, what its used for). The water jet force will drop off very quickly once released from the nozzle but if it is strong enough to knock caked on mud of it is strong enough to penetrate the bearings.
Bicycle seals (even the expensive ones marketed as 'sealed bearings' are not what I would call sealed) use grease and rubber bushings at atmospheric pressure to prevent water ingress into places where it shouldn't go. This works fine to keep splashed water from normal use out of contact surfaces, but not a focused pressurized jet of water from a standard 100bar pressure washer, lets say conservatively (it will probably be much more) the effective force of the water jet when it hits the bike to remove mud / grime is at least 20 bar this is equivalent to taking the bike to 200m + water depth - (you could estimate the force by firing the jet at a set of scales and dividing the the reading by the cross sectional area of the water jet). More than enough to deform the rubber seals and push out the grease.
Another issue is that water under tremendously high pressures will dissolve large amounts of atmospheric gas such as CO2 and Oxygen and become acidic and corrosive, once inside the bearing the pressure is released so the water stagnates and cannot get back out because of the rubber seals, so you have a perfect corrosion circuit consisting of water, carbonic acid and oxygen in constant contact with the steel, this can lead to extremely high corrosion rates even with corrosion resistant materials such as stainless steels or nickel alloys.
If when you took your pedal apart there was an orange brown sludge inside the bearing, it is a sure sign water has got in there and the most likely source is your pressure washer.
WOW nicely concise, thanks for that.
ReplyDeleteAn engineer myself (a career or two ago) I understand most of that, the change in gas is interesting though and I have seen the orange sludge before, in cheap forks from 15 years ago (long before I could afford a pressure washer!)
When My pedal blew it was full of lovely clean grease which did surprise me.
I have never had a problem with bottom brackets since I started using a pressure washer funnily enough, probably because I service my bikes a lot more than I used to and new bearings are really very good compared to the old days.
If you had six or seven bikes to clean every day, how would you do it?