How to Pressurize or Depressurize a Damper Using a Needle Fill Tool

Short answer: no, you don't need nitrogen to pressurize a shock at home. Even if the manual says "nitrogen", here is the reality:

• Air is already about 78% nitrogen.
• The remaining gases only matter at extremely high pressures (1000+ psi), which MTB dampers never reach.
• Thermodynamic differences exist, but at typical IFP pressures (100–300 psi) they are irrelevant in practice.
• Fox themselves recommend air for forks and most shocks.
• Nitrogen is mainly used for lab repeatability, compact design constraints, and slightly better pressure retention after pump removal.
• Shocks without a piggyback (Fox DPS, RockShox Deluxe) can run higher pressures (300–550 psi), which is intimidating but still manageable with the right pump and a tool rated for it.

Bottom line: a normal shock pump and air work exactly the same.

It comes down to space, mostly. A pellet is a hole in a top cap with a rubber plug in it. That is all. There is no valve body, no stem, no threaded adapter taking up room.

That buys a designer a lot:

• The reservoir can be made smaller
• You can charge a chamber in a very tight area, where a valve would never fit
• It is quick on an assembly line, which matters when you are building thousands of units
• It looks cleaner, with nothing sticking out of the damper

Some brands do go the other way. Older Fox Float X2 and DHX2 shocks (2016–2020) have a Schrader valve hidden under the cap, and DVO uses one too, which means you can change the IFP pressure yourself if you want to.

That is useful if you are struggling to land on the right spring rate. The IFP pressure acts like a small air spring: it pushes on the shaft and adds a little force in the damper. It is a very small force, so it is a fine adjustment rather than a way to make up for the wrong spring. It also means the brand has to give customers clear guidelines, since it is one more thing to get wrong.

For what it is worth, I am on the needle side. It is precise, it is quick, and I prefer it to a standard Schrader fill. If I ever built my own shock, that is the system I would use.

• A needle air fill adapter, rated for the pressure you are working at
• Hypodermic needles. 23 gauge, 25 mm (1 inch) is the sweet spot: short enough to stay stiff, cheap, and available anywhere
• A shock pump rated at least 300 psi, and a bench vise
• Shocks without a piggyback: 600 psi shock pump recommended, plus a fill tool actually rated for those pressures
• Eye protection
• A sharps container for used needles
• A pellet retainer tool, only if your shock uses one (see below)

Check your fill tool's pressure rating before you start, and know what the chamber is sitting at. Most dampers run at or below 200 psi, but the inline ones do not.

Most shocks do not. This trips people up, because guides tend to describe the retainer as a standard step when only a handful of models actually use one.

How to tell, by looking: if the chamber is closed by a 4 mm Allen plug and you can see the pellet sitting down inside the hex, that shock takes a pellet retainer.

Models that use one:

• Bomber CR
• Van RC
• DPX2
• Old Float X CTD
• Cane Creek DB Inline

Not many others do. On Öhlins, Push, Vorsprung, EXT and most other brands, you simply push the needle through the puck and that is it. Nothing to install, nothing to tighten.

If you do need one, match it to the pellet: a metal retainer for the harder Fox pellets, a plastic retainer for the soft Cane Creek ones.

1. Disconnect the shock pump. Use the fill tool with nothing attached to its Schrader port, or use a bare needle on its own. This is the whole point: the gas needs an open path out.
2. Insert the needle into the centre of the pellet while rotating it gently. Do not force it.
3. Let the pressure vent through the needle. The needle bore is small, so it bleeds down in a controlled way rather than all at once.
4. Remove the needle once it stops hissing.
5. Open the bleed screw very slowly.
6. If the damper is highly aerated and the IFP is fully seated:
   • Place the shock inside a sealed plastic bag.
   • Carefully open the bleed screw through the bag.
   • Never point the port toward yourself. Pressurized oil can eject several meters. Wear eye protection.

If you want to watch the pressure drop on a gauge instead, that is what a purpose-built high-pressure release tool is for. Do not improvise it with a pump attached to a fill tool.

1. Make sure the damper is fully reassembled and the shaft is fully extended, including the correct IFP depth if applicable (not applicable to bladders).
2. Fit a fresh needle to the fill tool and thread the tool onto your shock pump. Snug both, but only lightly. Overtightening the needle can bend the slip fitting when you pull it back off.
3. Only if your shock has the 4 mm Allen plug: install the pellet retainer into it. On every other shock, skip this step.
4. Gently insert the needle into the centre of the pellet while slightly rotating it. Do not force it, or you may bend the needle and damage the pellet.
5. If you are using a retainer: tighten it just enough to hold the needle in place.
6. Inflate slowly with the shock pump, staying within your fill tool's rating.
7. Once target pressure is reached, pull the needle out quickly and immediately snug the pellet.
8. Pellet torque, where a retainer is used:
   • Fox: higher torque required
   • Cane Creek: very low torque, soft pellet
9. Cycle the shaft. It should return smoothly with no squishy feel.

Tools that seal slightly less tightly will drift down while you work. The fix is not to fight it: pump quickly, go a little past your target, and pull the needle as the gauge comes back through the number you want.

• Shorter needles bend far less. 25 mm holds up where 35 mm gives way.
• Never bend the needle. Rotate gently during insertion.
• Only use plastic pellet retainers on soft pellets.
• If pressure escapes after removal, retry calmly.
• Inconsistent rebound usually means a poor bleed or incorrect pressurization.
• Dispose of used needles in a sharps container or through a pharmacy needle disposal program. Do not assume your local bike shop takes them.