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Working Principle of Valve DTH Hammer and Valveless DTH Hammer
Aug 18, 2018

DTH Hammer.JPG


Working Principle of Valve DTH Hammer and Valveless DTH Hammer



DTH Hammer is the heart of the DTH  drilling rig. Its quality is directly affected by the drilling speed and drilling cost. The basic requirements for the impactor are: good performance parameters, high drilling efficiency: simple structure, easy to manufacture, use and repair; reliable parts and long service life: can work normally in various rock layers, such as aquifers.



1. Structure of valve DTH Hammer


DTH Hammer transforms the pressure energy of the compressed air into the mechanical energy of the broken rock through the movement of the piston.

DTH Hammer-1.jpg


DTH Hammer is coupled to the drill pipe by threads on the joint 1. The joint l is embedded with a cemented carbide column to prevent the impactor from being caught by the upper part falling into the material, reducing the friction between the outer cylinder 10 and the hole wall, and prolonging the service life of the impactor. The valve train is composed of a valve cover 6, a valve plate 7, a valve seat 8, and the like. The piston 9 is a hollow rod shaped cylinder. The cylinder is composed of an inner cylinder 11 and an outer cylinder 10. The annular space between the inner and outer cylinders is the intake passage of the front chamber of the cylinder. The outer cylinder is connected to all the parts of the impactor. The bushing 12 is located at the top end of the card bushing 15, and its front end portion is slidable in the bushing when the piston is moved. The card bushing 15 is coupled to the outer cylinder by threads and drives the drill bit 23 to rotate by means of splines on the inner wall thereof. The drill bit 23 is an integral spherical cylindrical drill bit. The tail of the drill can slide up and down within the card sleeve. In order to prevent the bit from falling off during lifting or lowering, the drill bit is connected to the card sleeve by the round key 17, and the round pin is blocked by the pin 13 and the wire 16 to prevent the bit from falling into the hole. The role of the disc spring 4 is to compensate for the axial wear of the contact parts, to ensure that the parts are pressed tightly, to prevent the high and low pressure chambers from communicating to affect the performance of the impactor, and to function as a vibration damper during operation.



In order to make DTH Hammer work normally in the aquifer, the GMD-2000 is equipped with a waterproof device. The waterproofing device is composed of a sealing ring 19, a check plug 20 and a spring 21. Under the action of the air pressure, the spring is in a compressed state, and the anti-plug is moved forward, and the air can enter the impactor. When the air supply is stopped, the stop plug automatically closes the air inlet under the action of the spring. The gas inside the impactor is blocked, preventing the gushing water in the borehole and pouring the sand into the impactor.




A replaceable throttle plug 5 is provided between the bonnet and the valve seat to replace the throttle plug according to the specific gravity of the rock and the wind pressure, and the air volume and the air pressure are adjusted by the orifice of the appropriate diameter to ensure sufficient The large return air speed makes the bottom of the hole clean.


During the drilling process, it is sometimes necessary to deliver pressure to the impactor while lifting or lowering the drill to inject the rock that is accumulated at the bottom of the hole or to handle the clamp. At this time, if the impactor continues to impact, it is bound to empty the drill bit, which is easy to damage the parts such as the card sleeve, which is called the air strike phenomenon. The impactors are designed with a runaway structure. When lifting or lowering the drill, the drill bit falls by its own weight, its tail is stuck on the round key, and the piston is also at the lower limit position. At this time, the air intake hole 6 on the inner cylinder wall is blocked by the piston, exposing the hole 5, the piston An annular space formed between the constricted portion of the front end and the inner bore of the bushing allows the front cavity to communicate with the bottom of the hole, and the front cavity gas is discharged to the bottom of the hole. The compressed air entering the back chamber from the hole 5 directly blows the bottom of the hole through the center hole of the piston, and the piston stops moving, thereby eliminating the air-bending phenomenon. The hole 5 is usually referred to as a run-flat hole.



2, The Working Principle of Valve DTH Hammer


When the drill bit does not touch the bottom of the hole, the drill bit and the piston are at the lower limit position, and the pressures on the front and rear sides of the valve piece 7 are equal, and fall on the valve seat 8 by its own weight. The compressed air input by the hollow drill pipe enters the rear joint, compresses the spring, pushes the anti-reverse plug, and splits into two. All the way into the stop plug hole 1, through the bonnet, throttle plug, valve seat, piston and the center hole of each part of the drill bit to blow the bottom of the hole; the other way through the bonnet axial hole 2, through the rear side of the valve plate and the bonnet The gap between the holes enters the hole 4, passes through the annular air passage between the inner and outer cylinders, enters the rear cavity from the air-proof punching hole 5, and is discharged to the bottom of the hole.


DTH Hammer-2.jpg


When the drill bit touches the bottom of the hole, the tail end of the drill bit lifts the piston, so that the rear end of the piston blocks the air-proof punching hole 5, and the front cavity air inlet hole 6 is exposed, thereby pressing the air into the front cavity, and the front end sealing surface of the piston seals the front cavity. As a result, the pressure in the anterior chamber rises, the pressure pushes the piston back, and the piston starts to accelerate. The rear chamber gas is discharged from the center hole of the piston. When the center hole of the piston is blocked by the valve rod on the valve seat, the gas in the rear chamber is compressed and the pressure is gradually increased. The piston continues to move backwards, and when the front end of the piston is disengaged from the sealing surface of the bushing, the front chamber air pressure is discharged from the center hole of the drill bit. At this time, the pressure in the front chamber gradually decreases, and the pressure on the rear side of the valve plate also gradually decreases;




At the same time, due to the venting of the front chamber, the air flow velocity on the rear side of the valve plate is increased, and the pressure on the rear side of the valve plate is also lowered. The piston continues to move backwards by inertia, and the pressure in the rear chamber rises continuously, and the pressure acting on the front side of the valve plate also rises. When the pressure acting on the front side of the valve plate is greater than the pressure on the rear side of the valve plate, the valve plate moves backward, closing the hole 4 in the valve cover, opening the axial hole 3 on the valve seat, and the valve piece completes one reversal. The compressed air from the hole 2 is diverted through the hole 3 into the rear chamber of the cylinder. At this point, the piston continues to decelerate until it stops and the return journey ends. The two small holes in the valve seat are to increase the pressure in the rear chamber, to prevent the piston from striking the valve seat, and to have a certain thickness of the air cushion when the piston stops.



 After the end of the piston return stroke, as the rear chamber continues to intake, the back chamber pressure rises, pushing the piston forward and the stroke begins. The anterior chamber gas continues to be discharged from the center hole of the drill bit. When the front end sealing surface of the piston enters the bushing, the front chamber exhaust passage is closed, the gas is compressed, and the pressure rises. When the rear end of the piston disengages from the valve rod on the valve seat, the rear chamber begins to vent, and the piston still moves forward at a high speed until the end of the impact bit, and the stroke ends. Before the piston impacts the tail of the drill bit, the pressure in the rear chamber gradually decreases, and the pressure on the front side of the valve plate also decreases. At the same time, due to the exhausting action of the rear chamber, the airflow speed on the front side of the valve plate is increased, and the front side of the valve plate is also increased. The pressure is reduced. As the front chamber pressure continues to rise, the pressure on the back side of the valve plate also increases. When the pressure on the rear side of the valve plate is greater than the pressure on the front side, the valve plate moves forward, covering the intake passage of the rear chamber, and the air is re-entered into the front chamber to start the next working cycle.




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External rotation





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Inner rotation



3. Working Principle of Valveless DTH Hammer


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During the stroke, the compressed air enters the rear chamber through the annular space between the inner and outer cylinders 1, the inner cylinder radial bore 3 and the longitudinal groove 2 on the outer surface of the piston head, pushing the piston to perform a stroke motion. The anterior chamber gas is discharged to the bottom of the hole through the inner air passage 4 of the guide sleeve and the center hole of the drill bit. When the sealing surface of the piston is closed, the groove air passage 2 is closed, the rear chamber stops the intake air, and the piston continues to move forward by the expansion of the gas in the rear chamber. When the small head of the piston closes and passes over the air passage 4, the gas in the front chamber is compressed. When the front sealing surface of the large head of the piston is disengaged from the inner cylinder wall, the compressed air enters the front chamber, and the piston continues to advance by inertia. When the piston is disengaged from the valve rod, the rear chamber gas is discharged to the bottom of the hole through the center hole, and then the small head of the piston strikes the tail of the drill bit, and the stroke ends.


During the return stroke, the compressed air enters the front cavity from the air passage 4 via the air passage 1, the hole 3, and the annular space formed by the longitudinal groove 2 and the spacer on the piston, and pushes the piston for the return movement. The back cavity gas is discharged through the center hole. When the front sealing surface of the large head of the piston enters the inner cylinder, the pressure passage that enters the front chamber is cut, and the piston continues to return after the gas expansion of the front chamber. When the piston enters the valve rod, the rear chamber gas is compressed. When the small head of the piston passes over the air passage 4, the gas in the front chamber is discharged through the center hole of the drill bit. When the sealing surface of the piston is removed from the inner cylinder, the compressed air enters the rear chamber through the gas 3 and the longitudinal groove 2 on the piston, and the piston continues to decelerate until it stops at the top dead center, and then begins the next impact cycle.




Comparison of Valve DTH Hammer and Valveless DTH Hammer


DTH Hammer With Foot Valve.jpg

Valve DTH Hammer





DTH Hammer Without Foot Valve.jpg

Valveless DTH Hammer

 The valve reversal of a valve impeller is related to the exhaust pressure of the cylinder. Only when the exhaust port is opened and the pressure in the cylinder drops to a certain value, the valve is reversed. Therefore, from the time when the piston opens the exhaust port until the valve is reversed, the compressed air is exhausted from the exhaust port, and the energy of the compressed air is not utilized.


The valveless DTH Hammer utilizes the expansion of the compressed air to push the piston. The energy consumption is reduced, the gas consumption is about 30% lower than that of the valve impactor, and the impact frequency and the large impact energy are high. However, the main parts of the valveless impactor have higher precision requirements and the machining process is more complicated.


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