Short answer
A breaker with low nitrogen pressure strikes weakly, drops in blow rate and runs unusually hot at the back head. Pressure falls for three reasons: seals ageing and leaking, the slow natural loss of gas over time, and damage to the diaphragm or accumulator. Always measure with the breaker COLD — a hot breaker reads higher than the true value. The correct charge pressure is model-specific and is stated in your breaker manual.
What the nitrogen actually does
The back head of a hydraulic breaker holds pressurised nitrogen. As the piston rises it compresses that gas; the gas then acts like a spring, pushing the piston back down and adding energy to the blow. Part of the impact energy therefore comes from the hydraulics and part from the gas.
In HKM Grey Line breakers nitrogen is the primary energy source. In Red Line hybrid breakers gas and hydraulics work together to produce higher impact energy. In both cases, when gas pressure falls the breaker loses power — but it does not fail outright, it simply weakens gradually. That is what makes it hard to notice.
Why the pressure drops
- Seal ageing: the back head seal hardens over time and starts to leak. This is the most common cause by far.
- Natural loss: the nitrogen molecule is small, and even a sound system loses a little pressure over a long period. This is normal, and it is why periodic recharging exists.
- Diaphragm damage: on accumulator models, a ruptured diaphragm lets gas pass to the hydraulic side. Pressure then drops suddenly and the breaker becomes noticeably weak.
- Bad charging: a valve left leaking during charging, or an adapter that did not seat properly, loses the charge within a short time.
- Overheating: continuous blank firing or inadequate oil cooling raises back head temperature and shortens seal life.
Symptoms: what the breaker is telling you
The classic symptom of low nitrogen pressure is a blow that has gone soft. The crack it opened in the same rock yesterday will not open today, and the operator has to hold the breaker on one spot for longer.
The second symptom is rhythm. As pressure falls the piston returns more slowly; blow rate drops and the sound becomes sparser and duller.
The third is heat. Energy that cannot become impact becomes heat instead, and the back head gets too hot to touch. On its own this can also be caused by excessive oil flow, so read it together with the other two symptoms.
The most common mistake
A weak breaker usually gets a new tool first, then someone starts adjusting the hydraulics. The order should be reversed: measure nitrogen pressure first, because it is both the easiest thing to check and the most frequent cause.
How to measure it properly
Measure with the breaker cold. The back head of a breaker that has been working is hot, the gas expands and the gauge reads above the true value. A reading taken hot and judged "normal" turns out low once the machine cools. The best time is at the start of a shift, before the breaker has worked.
Use the breaker charging kit: a regulator with gauge, the adapter and a nitrogen bottle. The adapter must seat fully on the charging valve; a loose connection both misreads and vents gas while you measure.
Work with the breaker still on the carrier, tool resting on the ground and hydraulic lines depressurised. Charge with nitrogen only — never oxygen or compressed air.
Why we do not print the value here
Charge pressure differs for every model and depends on the line, the size and the back head type. The "so many bar" figures circulating online belong to other manufacturers, and the wrong pressure does a breaker no favours. The correct figure is in your breaker manual. If you do not have the manual, send us the model code and we will look it up.
How often should it be checked?
The rule that works in practice: look at it at every tool change. The breaker is already stopped and cool at that moment, so it costs no extra time.
Beyond that, follow the maintenance table in your breaker manual. On hard-working sites — continuous quarry work, hard rock, high ambient temperature — the interval shortens.
If pressure falls quickly between two charges, the problem is not the charging but a leaking seal or a damaged diaphragm. Repeatedly topping up the gas only delays the failure.