Short answer
Once tonnage fits, the second criterion is hydraulic, and it is read from two figures: oil flow (l/min) and operating pressure (bar). Below the range the attachment works slowly and weakly; above it, the excess flow turns into heat, the oil warms and seal life shortens. Pressure sets the impact energy of the attachment, and going outside its range causes mechanical damage directly. The figure in your machine manual is the one given for the attachment line, and it must not be confused with total main pump flow.
What flow tells you
Oil flow is the amount of oil delivered to the attachment per unit of time, and it sets working speed. On a breaker this is blow rate directly: more flow, faster piston cycling.
Stay below the range and the breaker strikes slowly and produces little. The operator usually reports this as "the breaker is weak" and nitrogen pressure gets the blame, when the problem is the flow the machine delivers.
Go above the range and the excess does not become work, it becomes heat. Breaker and oil run hot, seals age faster, internal leakage grows. It can look faster in the short term while eating component life in the long term.
What pressure tells you
Operating pressure is the force level the attachment was designed around. On a breaker it relates directly to impact energy.
If pressure is low the blow stays weak; the breaker runs but cannot break the material. If it is high, impact energy exceeds the design limit and loads on the body, the tie rods and the seals all rise.
Pressure is therefore a less forgiving criterion than flow. Some deviation in flow can be tolerated; going outside the pressure range produces damage directly.
A common reading mistake
A machine manual lists several flow and pressure figures: total main pump flow, the bucket circuit, the attachment (hammer) line. The one to compare against is the attachment line figure. Comparing total pump flow with the attachment figure creates the appearance of a match that does not exist.
What the manual says and what the site delivers can differ
- If the attachment line was fitted later, actual flow can differ from the manual; line diameter and valve choice change it.
- Long hoses and many fittings cause pressure loss; what reaches the attachment is not what left the pump.
- Oil temperature affects viscosity and viscosity affects flow. The same machine behaves differently on a cold morning and in the afternoon.
- Pump efficiency falls as a machine ages; on a ten-year-old machine the plate figure may no longer reflect reality.
- The only way to be sure is to measure. Your service can measure flow and pressure at the attachment line.
What to do if you are outside the range
If flow is too high, most machines allow the attachment line flow to be adjusted. That is not slowing the breaker down but running it at its correct speed, and heat drops after the adjustment.
If flow is too low, look at the line first: a narrow hose, a blocked filter or a wrong valve setting are common causes. If the machine genuinely cannot deliver, moving to a smaller attachment is the right decision.
If pressure is outside the range, look for an adjustment on the machine side rather than the attachment. Trying to raise the pressure of the breaker itself means pushing past its design limit.
The breaker selector on this site evaluates all three together: enter tonnage, flow and pressure and it shows what fits, and separately what matches your tonnage but not your flow.