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Check your nitrogen level in shocks !!! Here is how ...

This is a discussion on Check your nitrogen level in shocks !!! Here is how ... within the Suspension forums, part of the Technical category; There is so much talk of this shock vs. that one, re-valving, spring changes, etc. but almost none about checking and/or adjusting the nitrogen level. ...


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  #1  
Old March 22nd, 2009, 05:09 PM
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Check your nitrogen level in shocks !!! Here is how ...

There is so much talk of this shock vs. that one, re-valving, spring changes, etc. but almost none about checking and/or adjusting the nitrogen level. Now that my new profession is in pressure calibrations (on the international standards level down to parts per million) figured I have no excuse to be one of the few to put together a system to do it since have suspected low nitrogen in my shocks for a while. Not saying spring and valves are not important, but nitrogen is just as important.

Check your pressures frequently. They are going to leak over time and change with temperature similar to a tire. Many have found even brand new shocks are very low. Without proper nitrogen level they will not perform. You can also adjust them as part of your tuning. My Walker Evans are 150 PSI normal but can take them up to 200 PSI. I just set mine up properly after doing spring changes and re-valves and this had the biggest and best effect on my long travel performance. Mine are currently set to 170 PSI.

Make note that shocks use nitrogen and not “air”. Do not fill them up with air. The density is about the same but other properties (mostly being “dry”) make it more suitable for shocks. I am not a shock expert so maybe someone else can go more into why this is critical.

First task is to get the proper system for the task. If you run some searches for complete systems you will find there are few out there and they run from about $350 to $500 and some did not look to me like they would really work that great. Best choice is to build your own, but there are several things you need to understand to make sure it will work properly. Here is my new setup.


The most important thing to understand is this is not a simple pressure check like your car tires. It is fairly high pressure (usually 150 to 200 PSI) but more important it is a very small volume/amount of space holding this pressure (the remote reservoir). Assuming you have a tire gauge that can read up to 200 PSI (most don’t) you might assume you could just go check the pressure and verify if yours is ok since it does use a standard car tire Schrader valve. It is not that simple in a higher pressure and low volume situation. By the time a standard tire gauge seals with the Schrader valve the small leak that you hear equals roughly 20 PSI or more depending upon how quick and good the seal was. This also changes significantly with the type of gauge you are using. If it is a high quality one with big gauge and a short hose going to the gauge, that is more volume you have to fill with the nitrogen from the reservoir and thus the greater pressure loss even with an instant and perfect seal. This initial leak is relatively insignificant when checking a car tire as they are much less pressure and have so much more volume of air that they hold. Even if you have the type of adapter that screws onto the Schrader valve (Ex. mountain bike shock gauge) it will also leak before it makes the seal in tests I have done just as much as one you press and hold on.

The only solution I can find to the problem of making a seal before reading pressure is an adapter that screws onto the Schrader valve and then uses a plunger to press the inner pin that releases pressure.

Now that we have a solution for making a proper seal we have to figure out how to deal with the volume problem. From above, it is now clear that even with an almost perfect setup you are still not going to get a true indication of reservoir pressure due to the low volume as it has to fill the gauge up with nitrogen and thus gives you a false indication of what pressure WAS in there. The solution is you must use a complete system that has a nitrogen supply so you can fill all volumes and balance the reservoir pressure with the supply/source pressure. The plunger valve can then be closed when the complete system reaches the defined and balanced pressure so you can then be confident in your reservoir pressure.

Caution: High pressure gas is very dangerous. Do your own homework and get proper training before using a high pressure system. Below are just ideas and not recommendations.

So here is what you need for the complete system:

- Small nitrogen tank. A 20 cubic feet bottle is what I went with that holds about 2,000 PSI. Plenty of volume and pressure for several reservoir fills. Welding supply shops are usually the best source for nitrogen bottles. They do an exchange system similar to how most are familiar with a propane bottle exchange.
- Regulator. You don’t want 2,000 PSI going into your reservoir. It will blow up and be very ugly if not deadly. The regulator is used to adjust the 2,000lb or so pressure from the nitrogen bottle to the typical 150-200 PSI you want in your reservoir. Best to get one like I have pictured with two gauges so one reads your current bottle pressure and the other that reads you outlet pressure.

- High pressure/low volume hose to go from regulator to gauge (steel braided hose shown in first pic). Don’t want this too long or too big diameter as it just wastes nitrogen and becomes more dangerous. Three or so feet is good. Needs to be rated for more than your bottle pressure. Might need adapters to hook up to regulator that are also rated accordingly. Have the shop you get the nitrogen from help you with this also.
- Isolation valve (shown next to gauge in pic below). This helps protect the precision gauge discussed next as well as divides the volume when venting the line.
- Precision gauge. Needs to be rated for 200+ PSI but not too far over. Usually the regulator outlet gauge is used for a rough idea of the pressure you have coming out as it usually covers higher range and thus can not dial in +-5 PSI. Highly recommended you use a more precise gauge. I like the new digital gauges and found mine off eBay (JNK) from China. Key is to find one that has standard adapters so you can hook it up in your system. I tested it with my precise equipment at work and it was accurate enough for this application (+-.5 PSI across the range which is ten times greater than what I am try for),

- 200+ PSI rated hose to go from precision gauge to Schrader valve adapter (yellow hose shown above). Low volume and short length again. Might be a good idea to use a high pressure 2,000+ PSI hose just incase someone opens the regulator all the way open or something “weird” happens.
- The proper Schrader valve adapter with plunger. I could only find this on a partial “cheap” nitrogen shock pressure solution from Power Tank and disassemble it to integrate in my precision gauge instead of their super cheapo quarter sized gauge that does not have the proper resolution.

The above system cost me about $250 by the time I got the nitrogen bottle filled and could have been cheaper if I was not a little rushed to get it all put together.
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  #2  
Old March 22nd, 2009, 05:09 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

Here are the instructions to test your nitrogen pressure:

- Check all reservoirs you will fill to ensure the Schrader valve going into them is tight. WER’s are a standard NPT adapter sealed with Teflon tape and they can certainly come loose and leak.
- Disconnect reservoir from RZR so you have good access to the Schrader valve
- Make sure to not over pressure you precision gauge during this procedure, especially if digital. Digital and analog gauges can easily be damaged and give inaccurate readings if they are accidentally over pressurized.
- Make sure plunger on Schrader adapter is turned all the way out
- Screw on Schrader adapter. Make sure to tighten with a wrench! It uses a copper seal ring so it needs to be torque'd down or will also leak. Use two wrenches so that one is holding the Schrader valve going into the reservoir. Again, it is only sealed with Teflon tape and you do not want to break the reservoir seal when tightening on loosening adapters onto the reservoir.
- Make sure isolation valve is closed
- Screw down plunger on Schrader valve adapter. You will now see a pressure on your precision gauge but again it is false. Will be much lower than what you actually had.
- Make sure regulator is backed off so no pressure to the outlet valve of the regulator.
- Open nitrogen bottle as slow as you can. These bottles are almost instant on 2,000 PSI but any precautions should be taken to listen for a leak before completely opening. Close immediately if leak is heard and fix.
- Open isolation valve.
- Open regulator valve slowly and watch both regulator outlet and precision gauges. Slowly adjust regulator valve until desired system pressure is reached.
- Once pressure is reached stop and let it stabilize for at least 10 seconds as it will likely change a little. It might be best to overshoot your desired pressure by a few PSI as most regulator valves are a variable volume needle type. What this means is even though when you back the regulator off it will not release pressure (it only increases pressure … unless an expensive self venting regulator is used) but it does pull the needle back, which increase volume ever so slightly, which in turn can be used to decrease pressure in very small and precise amounts. I found my regulator variable volume gave me about max -4 PSI change in my system when backing it off.
- Once your precise target pressure has been reached and is stable, back off the plunger on the Schrader valve adapter all the way. This seals off the reservoir. You can now be confident it has a known pressure in it.
- Close the valve on the nitrogen bottle.
- Close the isolation valve.
- Slowly crack open the Schrader valve adapter with two wrenches to prevent loosening the reservoir seal. It will release precision gauge volume pressure rapidly.
- Open isolation valve slowly to release regulator volume pressure.

Note, I tested the pressure at different settings on my adjustable shocks and it did not affect pressure. So, these adjustments are not changing the volume as might be expected. Guess I need to go do some shock research to see what these adjustments are actually doing. What this means is it should not matter what setting your shocks are on when checking reservoir pressure.

Anyone know who actually makes that Schrader plunger valve? I am sure Power Tank just re-brands it but could not find it even with the sources I have available to me.
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Old March 23rd, 2009, 05:53 AM
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Re: Check your nitrogen level in shocks !!! Here is how ...

good write up. when i got my new FOX's they were all off from what they were supposed to be.
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Old March 23rd, 2009, 06:02 AM
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Re: Check your nitrogen level in shocks !!! Here is how ...

good write up. I check nitrogen at every race and use the fill pressure as part of the tuning process.
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Old March 23rd, 2009, 06:32 AM
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Re: Check your nitrogen level in shocks !!! Here is how ...

You can get the no-bleed Schrader 556 chuck here:
Schrader 556 - SkyGeek.com
or
POWERTANK - CO2 Air Systems

This unit is really sweet--especially considering the low price ($79):

INFLATION UNIT - RE Suspension Inc.


I wish I had found this before I made my own. I would modify this one by adding a 1 foot hose between manifold & the valve. Much more convenient to use.

Todd,
One thing I didn't see in your excellent post was to make sure when you check or fill your shocks that you do them off the machine or at least jack it up so the suspension is hanging. The N2 pressure will be much higher with the shock compressed by the machine's weight and this weight will make your readings inconsistent.
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Old March 25th, 2009, 10:00 AM
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Re: Check your nitrogen level in shocks !!! Here is how ...

[/QUOTE]Todd,
One thing I didn't see in your excellent post was to make sure when you check or fill your shocks that you do them off the machine or at least jack it up so the suspension is hanging. The N2 pressure will be much higher with the shock compressed by the machine's weight and this weight will make your readings inconsistent.[/QUOTE]

Good point and I did overlook this. Think it gives some more insight into how the shocks function ... kinda obvious but it is a variable volume so as the shock compresses the volume decreases and thus pressure increases.

Nice find on the inflation tool as lower cost solution and I would add the tube too like you mention ... much better than the Power Tank low cost solution I bought but still going to be a little hard to resolve 5PSI increments.

Anyone know exactly what the adjsutable knob on the reservoirs do? I have not done any research but it seems likely it is a variable restriction and thus effects the nitrogen flow rather than the pressure. This would change the rate at which pressure changes are able to occur inside the shock.
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Last edited by twvette; March 25th, 2009 at 10:11 AM.
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Old March 25th, 2009, 10:10 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

.............................


Anyone know exactly what the adjsutable knob on the reservoirs do? I have not done any research but it seems likely it is a variable restriction and thus effects the nitrogen flow rather than the pressure. This would change the rate at which pressure changes are able to occur inside the shock.[/QUOTE]


The most adjusters on the reservoirs are a needle and set to restrict the flow of oil as it is being displaced from the shock by the shaft entering the shock body. Some are like a faucet. I guess that would be a seal and seat. Some are for fine tuning, others are just band-aids for poor valving. Either way they are effective.

Last edited by Makin' Trax; March 28th, 2009 at 07:52 AM.
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Old March 26th, 2009, 06:15 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

Does anyone know what varying the nitrogen pressure will actually do.
Will less pressure slow down the rebound? More pressure add preload?
I'll take nitrogen tank next trip to Glamis and try different settings, see what happens.
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Old March 26th, 2009, 08:30 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

The information was very impressive and well written, thanks all who contributed.
From what I have been told, Nitrogen molecules are larger than "air" and so will not leak as "much"
as air would also being a "dry" chemical will not absorb moisture.
The moisture can/will result in pressure differences when heated.
When checking car tires they are considered cold if driven less than a mile at lower speeds.
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Old December 8th, 2012, 04:38 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

Gotta love it when you pay a company to host your pictures, they sell out, and company taking over takes many many months to get your pictures back yet still trying to figure out their website ... damn Webshots/Smile ...

I have uploaded the pics that do not show above to another site and hopefully the direct links in my original post will come back some day. Here are the pics ...
Nitrogen Shock Fill System - TLWphoto's Photos
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Old December 8th, 2012, 05:35 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

Quote: Originally Posted by quadnkev View Post
.........From what I have been told, Nitrogen molecules are larger than "air" and so will not leak as "much" as air would. Also being a "dry" chemical will not absorb moisture.
Actually, somebody told you wrong! Air molecules are a mixture of Nitrogen, Oxygen, Carbon Dioxide, and other trace gases, and are MUCH larger at STP than just plain-old Nitrogen molecules (N2). And Nitrogen, like ANY other gas, will absorb or "adsorb" water molecules, just like air (and all of it's constituent gases) will. Just a FWIW.......

Cheers
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Old December 8th, 2012, 06:27 PM
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Re: Check your nitrogen level in shocks !!! Here is how ...

Quote: Originally Posted by BarRZR View Post
Quote: Originally Posted by quadnkev View Post
.........From what I have been told, Nitrogen molecules are larger than "air" and so will not leak as "much" as air would. Also being a "dry" chemical will not absorb moisture.
Actually, somebody told you wrong! Air molecules are a mixture of Nitrogen, Oxygen, Carbon Dioxide, and other trace gases, and are MUCH larger at STP than just plain-old Nitrogen molecules (N2). And Nitrogen, like ANY other gas, will absorb or "adsorb" water molecules, just like air (and all of it's constituent gases) will. Just a FWIW.......

Cheers
... and "AIR" is about 78% Nitrogen (N) and 21% Oxygen (O2)...
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