aiden hallam
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- Aug 18, 2002
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can you help, why do i have to use nitrogen in thr rear shock, what would happen if you just used air while down at the gas station, the same as for your tyres. cheers aiden
nitrogen or air
- Thread starter aiden hallam
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dirt bike dave
Sponsoring Member
- May 3, 2000
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In theory, pure nitrogen is better as contaminants and moisture in the air can gradually erode the bladder, possibly causing premature failure. Also, nitrogen is not explosive in the event of a freak accident.
In practice, there is little difference IMO. The bladders are pretty thick, air is mostly nitrogen anyay, and aluminum shock bodies are very unlikely to spark and explode in the event of a collision (you've already got a 3 gallon gas tank between your legs anyways, so it seems silly to worry about 100cc of compressed air)
As to whether a rider can 'feel' the difference between air and nitrogen at the same pressure, NO WAY.
I have used air once, on a KDX250. Most gas station compressors will not get high enough pressure, but those small air compressors used to inflate balls and car tires will.
In practice, there is little difference IMO. The bladders are pretty thick, air is mostly nitrogen anyay, and aluminum shock bodies are very unlikely to spark and explode in the event of a collision (you've already got a 3 gallon gas tank between your legs anyways, so it seems silly to worry about 100cc of compressed air)
As to whether a rider can 'feel' the difference between air and nitrogen at the same pressure, NO WAY.
I have used air once, on a KDX250. Most gas station compressors will not get high enough pressure, but those small air compressors used to inflate balls and car tires will.
aiden hallam
Member
- Aug 18, 2002
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- Thread starter
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cheers for the info on the rear shock, i will use air for now untill i can get some nitrogen.
Also on the subject of the rear shock, what sort of pressure should i pump it up to. The bike is a Kdx 200 (92) and i weigh 11 stones. someone said about 140 psi is thia about right.
Also on the subject of the rear shock, what sort of pressure should i pump it up to. The bike is a Kdx 200 (92) and i weigh 11 stones. someone said about 140 psi is thia about right.
canyncarvr
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- Oct 14, 1999
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From mx-tech: http://www.mx-tech.com/articleread.asp?ArticleID=26
Mine is 165psi. Note that the pressurization of the bladder isn't something determined by rider weight (re: your reference to number of rocks). Not related.
Some notes of interest in the above article(s) regarding temperature, too btw.
Cheers!
Mine is 165psi. Note that the pressurization of the bladder isn't something determined by rider weight (re: your reference to number of rocks). Not related.
Some notes of interest in the above article(s) regarding temperature, too btw.
Cheers!
BadgerMan
Mi. Trail Riders
- Jan 1, 2001
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Air is fine to use. The only draw back I can see is corrosion (resevior end cap ) due to the moisture in the air. Be sure to use at least 140 psi. At lesser pressures, you run the risk of sucking the seal head up into the shock body during a big hit. This will damage the seal and or the body.
Originally, Japanese shocks [& forks} came filled with fish oil. If exposed to oxygen or air containing oxygen- the stuff reacted [decomposed] and got smelling really bad - it also thickened up considerably. Nitrogen prevented this. With the new synthetic and even petroleum oils, there is very little if any reaction. Most air from compressors is pretty dry. The process of compressing it removes most all of the moisture [like wringing out a towel] and most compressors have a centrifugal separator to remove the rest.
GO ahead and air it up ! Those small 12v compressors pass the moisture right on through so maybe wait for a low humidity day.
GO ahead and air it up ! Those small 12v compressors pass the moisture right on through so maybe wait for a low humidity day.
Rob, not meaning to flame you, but your statements are completely false and without facts. You obviously have deduced these things on your own...perhaps when you make a statement like this you should maybe look into some factual information to see if maybe what you are saying isnt complete drivel.
This issue is something I have a fair amount of experience with, so I will offer some of what I have learned.
First of all, when moisture (water) is in the vapor form, it is relatively harmless to nearly all pneumatic applications. However when this vapor changes to a liquid state, it can wreak havoc on nearly ALL pneumatic applications.
There is a fine line between vapor and liquid, this line would be called the Dew Point. The dew point is when vaporized water will condense to a liquid state.
Atmospheric air at 75degF and 75% relative humidity will contain one pound of water per 1000 cu. ft.
At 100psi. line pressure, free atmosphere is compressed as a ratio of 8:1 and 1000 cubic feet of free atmosphere will then become 125 cu. ft.
The 125 ft. of compressed air, at 100psi, will contain ALL of the contaminants of the 1000 cu ft. of free atmosphere inlcuding the one pound of water vapor.
Due to the heat of compression, nearly all of the water contamination will remain in vapor form immdiately after the point of compression. However when the due point is reached, all of this water vapor condenses and will be liquid contamination.
Just for an example of how much water can be produced with a compressor:
At 75degF and 75% relative humidity and 125cfm at 100psi, the potential of water content of the compressed air lines is 125cfm=1 pound of water/minute, 60 pounds of water per hour, 1440 pounds of water per day, 10,000 pounds of water per week,or 1,210 gallons per week.
Normal shop compressors will not create the example CFM, but it gives you a good example of how much water can potentially be in your air lines.
If you do have an air compressor then you know that the reciever tank will and does collect water. The collection is intially in vapor form, but due to the condition of dew point, the water condenses to a liquid state inside your compressor tank. Just open your drain at the bottom of the tank and you will see the result. BUT, this is not all the water that was in the air. Much of it still remains in the air that has exited the tank.
Not only does the air provide contamination water to your compressed air, it also causes oxidation of the tank and line metal introducing another contaminate to deal with...iron oxide.
With filtering of the compressed air, some of the moisture can be removed at the point of use. Also some of the solid cantaminate can be removed. However, with normal filters on the market, complete removal of the water is not possible. Also, a normal air filter will cleanse the air down to a point of 40 microns solids. This means that if there is iron oxide, the filter will keep any particles of it from passing IF they are larger than 40 microns in size. This cleansing is fine for some applications, but when we are talking about seals and bladders, 40 microns just doesn't cut it. A particle of oxide as small as 10 microns can kill a seal fast. (40 microns is the smallest size of any particle that we can see with the eye...this is why filter mfg's just make filters that cleanse to 40 microns...out of sight, out of mind)
Also, normal filter rigs do not remove all of the water, in fact they remove very little water form the air. So the water contamination, as well as other contaminants, will remain in your shock even if you filter it with normal filters.
There is a solution to the problem though. If you use a filtering process called "Coalescense" virtually ALL of the moisture can be removed from the compressed air. Also with proper filtration, solid contaminants can be removed down to a point of .01 microns. Only when you have filtered your compressed air with proper filtration equipment should it ever be used in a shock.
Any particulate or water left in the air can damage seals, and the water can also cause catostophic problems when it freezes. Not to mention the vast varying the air in the shock will undergo with temp changes, due to the water content.
So, unless you have proper filtration equipment at the "point of use" then using compressed air for your shocks is a mistake. Although they won't show such a drastic problem as a bad filled shock will, tires aired up without proper filtration can change with the temperature due to the water content. That is why you can have a given psi in your tires in the morning, but when you check them later in the heat of the day, they will have changed. Proper filtration can eleviate this condition as well.
I have what it takes, but I don't want to SPAM, so PM me if you are interested.
rethnal, Air doesn't draw moisture...but rather retains different amounts of moisture due to certain conditions. At a given temp. and relative humidity, air will retain X amount of moisture, no more no less.
Houndog, that's quite an expensive way to run pneumatic tools. Also, those racers can use air with the same results as the nitrogen fill IF it is filtered properly.
Houndog, that's quite an expensive way to run pneumatic tools. Also, those racers can use air with the same results as the nitrogen fill IF it is filtered properly.
." However when the due point is reached, all of this water vapor condenses and will be liquid contamination."
"If you do have an air compressor then you know that the reciever tank will and does collect water. The collection is intially in vapor form, but due to the condition of dew point, the water condenses to a liquid state inside your compressor tank. Just open your drain at the bottom of the tank and you will see the result. BUT, this is not all the water that was in the air. "
Exactly as I said ... when you compress air, [after it's cooled back to ambient] you remove water in the same ratio as it is compressed...just like wringing out a towel.
. "Much of it still remains in the air that has exited the tank."
That depends on what your definition of the word "Much" is. At your 8:1 compression ratio, the entire volume in the tank will then contain 1/8 or 12.5% the amount of moisture it originally contained. You are correct about mechanical filtration being inefficient. We have 3 - 10HP compressors here in our glassblowing shop which we use for oxygen generation. These run at 175psi so we get even more water out in the tanks. There are 2 centrifugal water filters in series and the downstream one makes a bit of water if the air heats up. We also use a coalescing filter just before the oxy generator to remove oil. [By the way -and the mfg. doesn't recommend it- you can flush a coalescing filter with naphtha, then purge with air and restore it to "new" condition.] Back to Bikes, I've used air in my shocks for years and never have seen any corrosion or experienced riding problems.
"If you do have an air compressor then you know that the reciever tank will and does collect water. The collection is intially in vapor form, but due to the condition of dew point, the water condenses to a liquid state inside your compressor tank. Just open your drain at the bottom of the tank and you will see the result. BUT, this is not all the water that was in the air. "
Exactly as I said ... when you compress air, [after it's cooled back to ambient] you remove water in the same ratio as it is compressed...just like wringing out a towel.
. "Much of it still remains in the air that has exited the tank."
That depends on what your definition of the word "Much" is. At your 8:1 compression ratio, the entire volume in the tank will then contain 1/8 or 12.5% the amount of moisture it originally contained. You are correct about mechanical filtration being inefficient. We have 3 - 10HP compressors here in our glassblowing shop which we use for oxygen generation. These run at 175psi so we get even more water out in the tanks. There are 2 centrifugal water filters in series and the downstream one makes a bit of water if the air heats up. We also use a coalescing filter just before the oxy generator to remove oil. [By the way -and the mfg. doesn't recommend it- you can flush a coalescing filter with naphtha, then purge with air and restore it to "new" condition.] Back to Bikes, I've used air in my shocks for years and never have seen any corrosion or experienced riding problems.
BadgerMan
Mi. Trail Riders
- Jan 1, 2001
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I think they use a nitrogen-generating-compressor-type piece of equipment (don't know the technical term!) rather than bottled nitrogen. I know that such a unit exists because they use them to air up truck and car tires as well as aircraft tires. I don't think they produce pressures high enough for charging a shock though.
The main reason they use nitrogen in aircraft tires is so there is no moisture to freeze at high altitudes.
I read somewhere that nitrogen is used in truck tires because it does not permeate through the rubber so you don't have to constantly monitor the pressure. FWIW.
They market nitrogen for use in car tires so that the moisture does not corrode aluminum rims.
Not that expensive considering its use, mostly at the track. They bring in T1 size bottles that would last a long time, filling tires and running the air gun. The other option for the airgun involves and external source of power or generator, but usually not supplied by the track. Some teams do have generators for lights, etc and the odd team brings a small mig welder. At least thats what they do at the local tracks here.
canyncarvr
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- Oct 14, 1999
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Makes the $65 I spent for my last shock service all the more a better deal.
If someone else were to ride my bike and have the opinion of the suspension that it was 'ok' maybe they'd be thrilled with air in their shock. Myself, I know my suspension is much better'n 'ok'...and I appreciate every one of the thousand bucks I've spent on it.
I'll stick with nitrogen....although I doubt the bladder cares whether it has a 40 micron something in it or not.......
If someone else were to ride my bike and have the opinion of the suspension that it was 'ok' maybe they'd be thrilled with air in their shock. Myself, I know my suspension is much better'n 'ok'...and I appreciate every one of the thousand bucks I've spent on it.
I'll stick with nitrogen....although I doubt the bladder cares whether it has a 40 micron something in it or not.......
BadgerMan
Mi. Trail Riders
- Jan 1, 2001
- 2,479
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That’s pretty much it in a nutshell!
Incidentally, I ran air in my YZF’s shock (160psi) all summer with no problems whatsoever. I subsequently found no corrosion inside the bladder either. I filled it using an ATB shock pump.
However, I was a little concerned about letting it set over the long winter with air in it because I will not be disassembling it every month or two.
I recently acquired a 20ft3 nitrogen bottle, regulator, 200psi hose, and all the related hardware at a welding supply shop for $150.00. It sure is a lot easier than stroking that ATB pump the hunnert times that it took to charge my shock!
Robcolo, at an 8:1 compression...and BTW that is not MY ratio, it happens to be the ratio air is compressed at....the reciever tank will not have 1/8th the amount it originally contained, but rather 8 times the amount, 800%. Think of it like this, it takes 8 cubic feet of atmosphere to create one cubic foot of compressed air. Lets assume the tank had 1 cubic foot of air when depressurized....at 100psi it has 8 times the amount of air, or 8 cu ft. The tank at this point also carries 8 times the contaminants and moisture that it did when depressurized. Also, when the tank collects water, it is NOT collecting ALL the water by any means. "Wringing out" might be a good description though...have you felt a rag after wringing it out? Is it dry? (btw...never use harsh solvents to clean coalescing elements...soap and water are sufficient)
Badgerman, This unit that does not use pressurized bottles of nitrogen...does it create the nitrogen by some process??? Or, is it possible that this unit you have seen could be a high tech air filtration unit...exactly as I have been describing?
Air does not permeate the rubber of the tire any more than nitrogen will, the use of nitrogen in tires is so the moisture issue is non-existant.
It's also non-existant with properly filtered, clean, dry air.
canyancarver, your shock does indeed care if it has 40 microns of contaminant as well as caring about having moisture placed in it. I'm only offering an alternative method to fill such items and at a reduced cost. Not to mention never having to fill tanks for shock charge again. Also, when you have such equipment, it can be used for precision tire fills, as we have dicussed, and also many other applications like power tool operation, plasma arc equipment, etc.
The US Navy utilizes portable coalescing filter units (the very ones I have) on board their ships. They use these units to power pneumatic tools such as precision torque wrenches used on the skin of fighter jets.
When talking about pneumatic tools, if they are kept lubricated they will run for a very long period of time UNLESS the air used to power them is contaminated with water, particulate, or other contaminants such as hydrocarbons that are naturally in our atmosphere.
Tools like plasma arc cutting rigs depend on clean, dry air for proper operation. If you've ever used one of these items you know that the tip doesn't last very long at all. They have to be changed frequently to produce a good cut. If you use a high-tech air filtration unit like I'm describing, the need for frequent change of tips goes away. For example, I know of a guy who used a plasma arc in a shop and changed tips approx 2-3 times a day....when he started using the proper filtration for the air, his tip changes went from 2-3 times a day to once every month or two.
Also a mfg company was spending about 1.2 million a year on pneumatic tool replacement until they went to proper point-of-use filtration....their expense went from 1.2 million a year to $27.00 the first year.(yes, twenty seven dollars)
Proper air filtration isn't for everyone. But it is available for those who are servious about clean, dry, ISO quality air.
Badgerman, This unit that does not use pressurized bottles of nitrogen...does it create the nitrogen by some process??? Or, is it possible that this unit you have seen could be a high tech air filtration unit...exactly as I have been describing?
Air does not permeate the rubber of the tire any more than nitrogen will, the use of nitrogen in tires is so the moisture issue is non-existant.
It's also non-existant with properly filtered, clean, dry air.
canyancarver, your shock does indeed care if it has 40 microns of contaminant as well as caring about having moisture placed in it. I'm only offering an alternative method to fill such items and at a reduced cost. Not to mention never having to fill tanks for shock charge again. Also, when you have such equipment, it can be used for precision tire fills, as we have dicussed, and also many other applications like power tool operation, plasma arc equipment, etc.
The US Navy utilizes portable coalescing filter units (the very ones I have) on board their ships. They use these units to power pneumatic tools such as precision torque wrenches used on the skin of fighter jets.
When talking about pneumatic tools, if they are kept lubricated they will run for a very long period of time UNLESS the air used to power them is contaminated with water, particulate, or other contaminants such as hydrocarbons that are naturally in our atmosphere.
Tools like plasma arc cutting rigs depend on clean, dry air for proper operation. If you've ever used one of these items you know that the tip doesn't last very long at all. They have to be changed frequently to produce a good cut. If you use a high-tech air filtration unit like I'm describing, the need for frequent change of tips goes away. For example, I know of a guy who used a plasma arc in a shop and changed tips approx 2-3 times a day....when he started using the proper filtration for the air, his tip changes went from 2-3 times a day to once every month or two.
Also a mfg company was spending about 1.2 million a year on pneumatic tool replacement until they went to proper point-of-use filtration....their expense went from 1.2 million a year to $27.00 the first year.(yes, twenty seven dollars)
Proper air filtration isn't for everyone. But it is available for those who are servious about clean, dry, ISO quality air.
canyncarvr
~SPONSOR~
- Oct 14, 1999
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Jaybird:
This is either a semantics issue, or I'm missing it....
Yes, "..your shock does indeed care if it has 40 microns of contaminant as well as caring about having moisture placed in it."
IF 'in it' means in the oil reservoir, shock body.
Are you saying it 'cares' if there is contamination to the extent of 40 microns in the bladder?
I'm not arguing one way or the other. I just want to be sure I understand what you are saying.
Your earlier comment of 'A particle of oxide as small as 10 microns can kill a seal fast' is curious if it's inside the bladder we're talking about.
That's what I was referring to.
Thanks for the elucidity (don't look that up......;) )
This is either a semantics issue, or I'm missing it....
Yes, "..your shock does indeed care if it has 40 microns of contaminant as well as caring about having moisture placed in it."
IF 'in it' means in the oil reservoir, shock body.
Are you saying it 'cares' if there is contamination to the extent of 40 microns in the bladder?
I'm not arguing one way or the other. I just want to be sure I understand what you are saying.
Your earlier comment of 'A particle of oxide as small as 10 microns can kill a seal fast' is curious if it's inside the bladder we're talking about.
That's what I was referring to.
Thanks for the elucidity (don't look that up......;) )
BadgerMan
Mi. Trail Riders
- Jan 1, 2001
- 2,479
- 10
Jay,
Here's the hype I read on the nitrogen topic. They say migrate rather than permeate. Oh well, take it FWIW.
I am far from an expert on the subject.
http://www.airliquide.com/en/medias/pdf/business/gases/supply/tires_filling.pdf
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dirt bike dave
Sponsoring Member
- May 3, 2000
- 5,348
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I can't see any reason to spread all the gloom and doom about using a little ol' air. The moisture and air contaminants are not mixing with the oil.
Let's review the function of the pressurized bladder. It pushes on the oil, keeping it under pressure, to reduce foaming/cavitation in the oil as the piston moves through it.
Maybe air in the bladder is a little more sensitive to temperature than nitrogen. So what? As long as you are close to spec, bladder pressure is not terribly significant, IMO. If it were, we would be checking our shock pressure before every ride, just like tires. Example: I fill my shock with NITROGEN on a 90 degree F day to 165 psi. If the temp drops to 50 degrees do I need to add a few psi? Even the complete perfectionists among us do not.
The temps in the shock reservoir and bladder will not boil water under 170 psi. And it would have to be extreme cold for any moisture in the reservoir to remain frozen as the bike is being ridden. And even if it did, how would a thin coat of frost on the inside of the bladder effect shock performance?
Let's review the function of the pressurized bladder. It pushes on the oil, keeping it under pressure, to reduce foaming/cavitation in the oil as the piston moves through it.
Maybe air in the bladder is a little more sensitive to temperature than nitrogen. So what? As long as you are close to spec, bladder pressure is not terribly significant, IMO. If it were, we would be checking our shock pressure before every ride, just like tires. Example: I fill my shock with NITROGEN on a 90 degree F day to 165 psi. If the temp drops to 50 degrees do I need to add a few psi? Even the complete perfectionists among us do not.
The temps in the shock reservoir and bladder will not boil water under 170 psi. And it would have to be extreme cold for any moisture in the reservoir to remain frozen as the bike is being ridden. And even if it did, how would a thin coat of frost on the inside of the bladder effect shock performance?
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I wonder if Jeremy ever explained the picture he posted of the shock body that had exploded.
dirt bike dave
Sponsoring Member
- May 3, 2000
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I remember the pictures (cracked YZ shock, I think) but never saw Jeremy or anyone else confirm the cause. I do not remember the owner saying he used air in the bladder. I do remember he had transported the bike in the back of a pickup during winter.
Are you saying that air caused the crack and the shock would not have cracked if nitrogen was used?
Are you saying that inflating the bladder with nitrogen offers performance benefits over air?
Are you saying that nitrogen offers reliability or safety benefits over air?
Are you saying that air caused the crack and the shock would not have cracked if nitrogen was used?
Are you saying that inflating the bladder with nitrogen offers performance benefits over air?
Are you saying that nitrogen offers reliability or safety benefits over air?
What I'm saying is that moisture in a shock is bad news. That is why nitrogen is used. I submit that there is another way of charging the shock and not have the moisture worries. I don't feel that there is perfomance gains by using nitrogen over air, unless the air has not been properly cleansed, then there is absolutely an advantage in using bottled nitrogen.
I don't think there ever was confirmation on the actual cause of the shock failure, but I would bet money moisture was involved.
I don't think there ever was confirmation on the actual cause of the shock failure, but I would bet money moisture was involved.
