1. General Description


The JOYTECH DTH hammers are valveless, pneumatically operated tools designed to use with 3" to 40" diameter bits in rock formations under a wide range of operating conditions.

The JOYTECH hammers incorporate thick hardened wear sleeves. The simple design of the JOYTECH hammers provides performance, dependability and ease in servicing.

The JOYTECH hammers are designed for universal applications using air pressure 100psi to 350psi ( 7bar to 24bar ), with some exceptions of special models.


2. Operation

- Check if the chuck and the backhead are firmly tightened.


- Lubricate the hammer with rock drill oil.

  DTH Hammers need 0.2 litre/hour of oil per 3m3/min of air consumed.


- Connect to the hammer to the drill string.


- Open the hammer lubricator valve to continually inject oil into the air stream whilst
ththe hammer is operating


- Start to drill after checking safety


- Rotation Speeds

  As a general guide, the harder the rock or the larger bit diameter, the slower the   rotation speed required.

  It may be necessary however to increase the rotation speed where the rock is
bbadly fissured in order to prevent stalling.


   Up Hole Velocity

·To provide an adequate speed to evacuate cuttings from a hole, drilled with a DTH    hammer, an uphole velocity of 900-1800 Metres/Minute (3000-6000 Ft/Min) is    required.


  The formula for calculating up hole velocity is as follows -


                   METRIC                                          IMPERIAL

     VM = X(M3) x 1,305,096                VF = Y(CFM) x 183.40
                     DM2 - dm2                                         DI2 - di2

Where -

VM = Velocity in metres per minute.
X(M3 ) = M3 /Min. of air volume passed by the hammer at the selected air pressure.

DM2 = Diameter of hole - squared (in millimetres).
dm2 = Diameter of drill tube squared (in millimetres).

VF = Velocity in feet per minute.
Y(CFM) = Volume of CFM of air passed by the hammer at the selected air pressure.

DI2 = Diameter of hole - squared (in inches).
di2 = Diameter of drill tube - squared (in inches).


  A. Establish the volume of air in M3 /Min. being passed through the hammer.

  B. Establish the velocity per M3 of air , from chart across, with relevant tube and
and hole diameter.

  C. Multiply A x B = answer in Metres/Minute.

  D. If Feet per minute required - Multiply Metres/Minute x 3.28.


   Thrust (Pulldown) / Holdback / Torque

  ·Thrust should be kept as low as possible at all times avoiding excessive vibration

    in the drill string.

· ·Holdback should be increased more and more as additional pipes are added,

    as drilling progresses.

· ·Although the base of the hammer should maintain contact with the bit, there
 be neither excess thrust nor vibration due to reaction between the hammer anandd the bit.

    Insufficient thrust will cause the hammer to bounce resulting in a low blow energy
 the rock causing vibration and also possible damage.

· ·DTH bits unlike rotary tricones require very little rotation torque


                                      Bit dia           Recommended Torque

                                     105mm                         50KGM

                                     127mm                       120KGM

                                     165mm                       250KGM

                                     200mm                       300KGM

                                     300mm                       350KGM

                                     445mm                       425KGM


   Drilling depth capability 

· ·The depth capability with DTH hammers is governed by two main factors,

    sufficient air volume to keep the hole clean and the drill rig's lifting power.

· ·On deep hole applications, such as water well drilling, it is essential that the drill
 has sufficient lifting power with a reserve of power (safety factor) for
such as the drill rig's hydraulic system inefficiency, the weight of
thethe rotary head
/hammer/bit, friction in the hole, potential hole collapse etc.

    In reality, only around half of gross lifting power can be used.


3. Maintenance


· ··Maintenance should be performed in a clean environment.

· ··Clean the outside of the hammer.

· ··Unscrew and remove the backhead from the wear sleeve.

· · Remove the backhead "O" ring and thrust washer from the backhead.

· · Remove the air check valve, the check valve spring and the check valve housing

     from the backhead and of the wear sleeve.

· · Unscrew and remove the chuck, bit and bit retaining rings from the wear sleeve.

· · Remove the chuck washer from the chuck.

· · Using a brass rod, slide the piston against the air distributor and push air
and O-ring out the backhead end of the wear sleeve.

· · Remove the bushing washer from the top of the air distributor.

· · Slide the piston out the backhead end of the wear sleeve.



· · After disassembling, wash the parts in a cleaning solvent.

· · Dry the cleaned parts using compressed air.





  Inspect the striking face for cracking and general wear.

  Examine the O.D. for pick-up and burning marks (a sign of poor lubrication)

  Using emery cloth, clean up the O.D. to a good working surface.



  If the outside diameter of the piston requires attention, then it is certain that ground

  registers inside the wear sleeve will require the same.

  Carefully refurbish with a hone attached to an extension rod.



  Inspect the O.D. for nicks, burrs and scoring.

  Remove all minor irregularities with emery cloth.

  Replace if necessary.



  The check valve should be smooth and free from abrasions.

  Replace if necessary.


      ·BACK HEAD

  Check make-up face, removing all nicks and marks.

  Remove all burrs on the thread area with a fine file.



  Inspect for damage such as cracks and deformations.

  Replace if necessary.



  Check for wear and cracks.

  Always try and keep the chuck diameter larger than the wear sleeve as this
the service life of the wear sleeve.


4. Troubleshooting - Hammer Malfunction 




Hammer does not start operating after pipe change


Excess oil drained down into hammer

Foreign particles in hammer

Hammer filled with water and mud, especially if drilling under water level



Lift off flush. Add small amount of diesel to flush through if necessary

Pull out and inspect hammer

Pull out and clean hammer. Ensure that hole is 'clean' before uncoupling pipes for pipe change.

Ensure non-return valve is fitted to hammer or fit intertube non return valve, if drilling in deep water

Hammer operates on the surface but fails to work when lowered into the hole

Bit flushing holes blocked with clay, or debris whilst lowering into the hole

Lowering into soft clay or similar, thereby not allowing bit to be pushed up into the hammer

Inspect and strip if necessary

Increase rotation speed and perhaps thrust to force through soft ground, keeping full air on at all time and lifting constantly to flush. Water injection can be used to break up soft clay

Hammer operates intermittently on surface test      or down-the-hole

Hammer parts worn, broken or seized

Hammer incorrectly assembled

Dirt or foreign particles in hammer

Excessive lubricating oil or other oil coming through the system

Excessive water in the compressed air

Hammer freezing

Strip, inspect and service

Strip and re-assemble correctly

Strip, clean and re-assemble

Check quantity of lubricating oil and for signs of compressor oil in the air line

Check moisture trap and water injection pump, if in use

Use antifreeze type oil-check for signs of excessive water in system

Hammer does not operate on surface test or down-the-hole

Insufficient or no air reaching hammer

Hammer incorrectly assembled

Dirt or foreign particles in hammer

Retained oil or anti-seize grease in hammer

Hammer parts worn, broken or seized up

Blockage in shock absorber

Flushing holes in drill bit blocked

Check compressor operation

Strip and re-assemble correctly

Strip, clean and re-assemble

Flush through hammer by lifting off the bottom of the hole.

Add a small amount of diesel to the hammer to clear the oil.  

Strip, inspect and service.

Unscrew hammer and check. Strip shock absorber if necessary.

Clean out holes.

Hammer deviates at the start of hole

Breakout table bushes not being used or ones in use badly worn

Mast not secured

Machine not stable

Jacklegs creeping due to slow loss of hydraulic oil

Obstruction at the top of the hole causing the hammer to deviate

Too high feed force (thrust)

Fit or replace bushes

Secure mast

Ensure machine is rigid. Place wood

blocks under jack leg if ground is soft. Ensure there is sufficient weight on Jack legs.

Repair jackleg

Remove any obstructions before drilling continues

Reduce feed force to correct level


5. Storage

When storing a hammer, it is important to take the necessary steps in order to insure a smooth operation after restarting.

When the hole is completed and the hammer is to be inactive for several weeks or longer the following steps should be followed:

Each drill pipe should be blown clear of all water. During this process, turn on the in line lubricator and blow until the rock drill oil can be seen from the bottom end of each drill pipe. In addition, each pipe (pin and box end) should be wiped clean and capped to prevent foreign contaminants from sticking to the connector ends. 


When a hammer will be stored for only a short period of time the following steps should be taken:

· · Blow the hammer clear of all water.

· · Pour 1 quart (1 liter) of rock drill oil into the backhead.

· · Turn the air on and cycle for 10 seconds. This will lubricate the internal parts.

· · Cap the backhead and chuck end.

· · Store the hammer horizontally in a dry environment.



When a hammer will be stored for a long period of time the following steps should be taken:

· · Blow the hammer clear of all water.

· · If at all possible, the backhead and the chuck should be broken loose on the drill

    This is much easier than trying to do so in the shop.

· · Disassemble the hammer.

· · Inspect and wipe all the parts clean.

· · Lubricate all the internal parts with Rock Drill Oil.

· · Cap the backhead and chuck ends.

· · Store the hammer horizontally in a dry environment.



Before restarting the hammer after prolonged periods of inactivity, disassemble and inspect all internal hammer parts.

If any internal hammer parts have oxidized, use an emery cloth to polish each part. Wash each hammer part, wipe dry, relubricate with Rock Drill Oil and reassemble the hammer.  

  Dahil Corporation