1, General
Series HD high air-press DTH are designed as a hammer drill. They differ from other rock drills, however, through continuous operation down against the drill bit. Compressed air is led to the rock drill thorough the drill tube string. Exhaust air is discharged through hole in the drill bit and used to flush clean the drill hole. Rotation is delivered from a rotation unit and feed force from the feed is transferred the DTH drill via the drill tubes.

2, Technical description
The DTH drill comprise a narrow elongated tube which contains an impact piston, internal cylinder, air distributor, check valve. The real, threaded top sub is fitted with a spanner slot and coupling thread for connection to the drill tubes. The forward parts, the driver check, also fitted with thread, enclose the splines-equipped bit shank and thansfers feed force as well as rotation to the drill bit. A stop ring limits axial movements of the drill bit. The purpose of the check valve is to prevent impurities from penetrating the rock drill when pressed air is shut off. During drilling, the drill bit is with drawn inside the DTH and pressed against the drive chuck. The piston strikes directly against impact surface of the shank of the bit. Air blowing occurs when the bit loses contact with the bottom of the hole.

3, Operation and maintenance
1, The drive chuck and top sub are threaded into the cylinder with right-hand threads. The drill must be always operated with right-hand rotation.
2, Start collaring with reduced throttle to the impact mechanism and feeding, let the bit work its way slightly into the rock.
3, It is important that the feed force is adapted to the weight of the drill string. The force from the feed motor needs to be corrected during drilling, depending on the variable weight of the drill string.
4, The normal rotation speed for DTH lies between 15—25rpm。The upper limit generally produces the best generation rate, however, in highly abrasive rock, rpm should be in order to avoid excessive wear of the drill bit.
5, Clogged or cave-in of the hole, can lead to a stuck drill. It is best therefore, to clean the hole regular intervals, by carrying out air-blowing with the rock drill.
6, Jointing operation is the work sequence where a down-the-hole drill is most likely to experience contamination, through cutting and various kind of impurities falling down the hole. Make it a rule therefore, to always cover the open the thread end of a drill tube during joining. Make sure also that the drill tubes are free from cuttings and dirt.
7, The importance of correct lubrication of the rock drill cannot be over-emphasized. In adequate lubrication accelerates wear and can ever lead to breakdown.

4, Trouble shooting
Fault 1 : Poor or no lubrication, causing increase in wear or scoring.
Cause : Oil is not reaching the impact mechanism of the rock drill.
Remedy : Inspect the lubrication, top-up with oil if necessary, or increase luboil dosage.
Fault 2 : Impact mechanism does not operate, or works with reduced effect.
Cause :
A, Supply of air throttled or blocked.
B, Too large a clearance, between the piston and the external cylinder, or between the piston and the internal, or between the piston and the air distributor.
C, Drill dogged by impurities.
D, Piston failure or foot valve failure.
Remedy:
A, Check the air pressure. Check that the air passages up to the rock drill are open.
B, Disassemble the rock drill and inspect the wear, replace worn part.
C, Disassemble the rock drill and wash all internal components.
D, Disassemble the rock drill replace the fractured piston or sit up a new bit.
Fault 3: Lost drill bit and driver chuck.
Cause : Impact mechanism has operated without right-hand rotation.
Remedy : Fish up the dropped equipment with a fishing tool. Remember to always use right-hand rotation, both when drilling and when lifting the drill string.