Method and system for determining a variation in a flushing medium flow and rock drilling apparatus

1. Method for determining a variation of a flushing medium flow at a rock drilling apparatus, where a compressor ( 8 ; 301 ) discharges a flow of pressurized gas, where said gas flow at least partially is used as flushing medium during drilling with a tool ( 3 ), wherein, during drilling, said flushing medium is led to said tool ( 3 ) for flushing away drilling remnants, the method including the steps of:

determining a rate of pressure variation representing a difference between a flow discharged by the compressor for use as flushing medium and an actual flow of said flushing medium at the tool, and

generating a signal of decreased flow of flushing medium at the tool when said determined rate exceeds a first value.

2. Method according to claim 1 , wherein said signal is generated first when said determined rate has exceeded said first value during a first time.

3. Method according to claim 2 , wherein said determination of said rate of a pressure variation is determined by means of consecutive pressure determinations, where said rate is determined according to

Δ

⁢

⁢

P

Δ

⁢

⁢

t

,

where ΔP is the pressure difference between the pressure determinations and Δt is the time between the pressure determinations.

4. Method according to claim 2 , wherein said determination of said rate of a pressure variation is determined by determining a derivative of the pressure variation of said flushing medium.

5. Method according to claim 2 , wherein said compressor ( 8 ; 301 ) is controlled such that a determined gas flow is discharged.

6. Method according to claim 1 , wherein said determination of said rate of a pressure variation is determined by means of consecutive pressure determinations, where said rate is determined according to

Δ

⁢

⁢

P

Δ

⁢

⁢

t

,

where ΔP is the pressure difference between the pressure determinations and Δt is the time between the pressure determinations.

7. Method according to claim 1 , wherein said determination of said rate of a pressure variation is determined by determining a derivative of the pressure variation of said flushing medium.

8. Method according to claim 1 , wherein said compressor ( 8 ; 301 ) is controlled such that a determined gas flow is discharged.

9. Method according to claim 8 , wherein said compressor flow is controlled by speed control and/or control of the inlet valve ( 302 ) of the compressor ( 8 ; 301 ).

10. Method according to claim 1 , wherein said determination of a rate of a pressure variation of said flushing medium is performed by means of a determination of a pressure variation on the high pressure side of said compressor ( 8 ; 301 ).

11. Method according to claim 1 , wherein said determination of a rate of a pressure variation of said flushing medium is performed by means of a determination of a pressure variation at a position between said compressor ( 8 ; 301 ) and said tool ( 3 ).

12. Method according to claim 1 , wherein said determination of a rate of a pressure variation is performed continuously or by, certain intervals.

13. Method according to claim 1 , wherein, during drilling, said first value is determined at least partially based on the flow discharged by said compressor ( 8 ; 301 ) and/or a pressure on the high pressure side of the compressor ( 8 ; 301 ).

14. Method according to claim 1 , further including determining the flow discharged by said compressor ( 8 ; 301 ) by means of a flow meter.

15. Method according to claim 1 , wherein said signal is only generated when a second time has lapsed since the drilling started.

16. Method according to claim 1 , wherein said determination of a variation of said flushing medium flow consists of a determination of a reduction of a flushing medium flow discharged at said tool ( 3 ).

17. Method according to claim 1 , wherein, when a maximum set flushing medium pressure has been reached, the flow of the compressor ( 8 ; 301 ) is determined, wherein said signal is generated when said flow is below a second value.

18. Method for determining a variation of a flushing medium flow at a rock drilling apparatus, where a compressor ( 8 ; 301 ) discharges a flow of pressurized gas, where said gas flow at least partially is used as flushing medium during drilling with a tool ( 3 ), wherein, during drilling, said flushing medium is led to said tool ( 3 ) for flushing away drilling remnants, the method including:

determining a rate of pressure variation of said flushing medium,

generating a signal when said determined rate exceeds a first value, and

determining a representation of the acceleration (second derivative) of said pressure variation of said flushing medium flow, wherein said signal is only generated when said acceleration exceeds a second value.

19. System for determining a variation of a flushing medium flow at a rock drilling apparatus, where a compressor ( 8 ; 301 ) is arranged to discharge a flow of pressurized gas, where said gas flow at least partially is arranged to be used as flushing medium during drilling with a tool ( 3 ), wherein, during drilling, said flushing medium is led to said tool ( 3 ) for flushing away drilling remnants, wherein the system includes:

first determination means for determining a rate of a pressure variation representing a difference between a flow discharged from the compressor for use as a flushing medium and an actual flow of said flushing medium at the tool, and

signal generating means for generating a signal of decreased flow of flushing medium at the tool when said determined rate exceeds a first value.

20. Rock drilling apparatus, wherein said apparatus includes a system according to claim 19 .