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Topeak Micro Rocket Pump — Design Defect Repair

This page describes a simple repair for a design defect in the Topeak Micro Rocket AL mini-pump. This is the 2008 model, but the 2011 model shown here (as of 2011/10) looks similar.

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The pump is about 160mm long, the body is about 20mm in diameter, and it weighs about 65g according to the maker (as is the measured weight of the pump here). Like most mini pumps, it is convenient to carry, and is easy to carry in a bag that "goes with", rather than being left on the bike and risking theft.

Also like most mini pumps, it takes very many strokes to inflate a tire to normal pressure, and is awkward to use. Which makes it especially aggravating that there are a pair of shoulders that are prone to pinch the user's hand while pumping:

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The "pinch point" is a design flaw, but it turns out to be easy to fix. First, there is a polished ring that unscrews away from the pump head:


Unscrew it completely. The pump has an outer shell with an O-ring which probably keeps the outer shell from rattling. It makes it hard to slide the shell. The following picture shows the outer shell has a detent that engages the pump head, so the head and shell turn together:


Hold the upper skinny part of the pump and turn the head counter-clockwise (as viewed from the head end) to unscrew the head. Note it is the standard threading, if that helps.

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This shows the pieces:


Screw the pump head back in to the pump body, leaving off the outer shell, O-ring, and shiny threaded ring:


No more pinch point — the pump is now easier to use.

The outer shell may protect the barrel against knocks and bumps, so the barrel may be easier to damage after this modification.

The pump is marginally smaller and weighs about 10g less. The pump shown here is 55g after modification, which is 10g lighter than the listed weight of the 2011 aluminum version and the same weight as the 2011 carbon-fiber version but without the pinch point.

The 2011 carbon fiber version listed here (as of 2011/10) says it has a "Carbon handle and barrel sheath". The modification shown here might also work on it. It seems likely the carbon tube weighs less than the aluminum one, so the weight savings would be less, but avoiding the pinch point should be a big win.

The T-handle versions shown here and here (as of 2011/10) avoids the pinch point, but the same modification might be possible, and if so would make the pumps marginally smaller and save about 10g from the aluminum pump's weight and some from the carbon fiber version. Since big reasons for carrying a mini-pump are to save space and weight, the modification may still be useful even though it does not avoid a pinch point.

Further Modifications

The pump also uses a latch built in to the handle. When the pump is stowed, it stays closed and thus minimizes risk of damage to the pump shaft. Also, during pumping before modification it reduces (but does not eliminate!) pinches.

With the pinch risk removed (as above), a further modification is to carve away the latch. This slightly extends the (very short!) stroke and in particular slightly eases/speeds the highest-pressure part of filling a tire.

Carving away the latch has the down side the pump can open when stowed, making the shaft easier to damage. In some uses, normal stowage does not allow opening so this is not a problem. Also, by carving away the material "mostly", some detent remains. The pump can still be pulled open, but it is less likely to open accidentlly.

There's probably many ways to carve away the latch. One is using a tapered (conical) bit in a Dremel™ or similar rotary grinder.