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.