Pressure relief valve for rock bits

A sealed rotary rock bit is disclosed in which a combined manual venting and pressure relief system is located within the lubrication reservoir of the rock bit. The seal rotary rock bit comprises a main bit body having a plurality of legs extending downwardly therefrom. Each leg has a rolling cone cutter rotatively mounted thereon. A lubrication system is provided in each leg to provide lubricant to the bearing area between the cutter and the leg. The lubrication system includes a reservoir of lubricant communicating via passageways with the bearing area. The reservoir further includes a rubber boot molded around a metal stiffener sleeve. A cover cap is attached to the rubber boot. The rubber boot is in the form of a resilient membrane and is exposed through the cover cap to the exterior of the rock bit and through the passageways to the interior of the lubricated bearing area. The vent and pressure relief system comprises an annular seat formed in the wall of the reservoir. A valve face is formed on the rubber boot and is biased against the annular seat by means of a belleville spring acting on the cover cap. If any excessive pressure develops within the lubricant reservoir, the excess is blown off through the valve seat. Any internal pressures can also be manually vented without removing the cover cap by a slight prying action on the cover cap.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to sealed rotary rock bits and, 
more particularly, to the lubrication systems utilized in such bits. 
2. Description of the Prior Art 
A rotary rock bit generally consists of a main bit body adapted to be 
connected to a rotary drill string. A conventional bit usually includes 
two or more legs integrally connected to form a bit body. Each leg 
includes a cutter rotatively mounted on a journal pin extending from the 
leg. Bearings are provided between the cutter and the journal pin to 
promote rotation of the cutter and means are provided on the outer surface 
of the cutter for disintegrating the formations as the bit and cutter 
rotate. 
In lubricated rock bits, a lubrication system is provided which includes an 
annular seal located at or near the back-face of the cutter to prevent the 
lubricant from leaking from the bearing area to the exterior of the rock 
bit and prevent drilling fluid and debris from entering the bearing area. 
The lubrication system further includes a reservoir filled with a 
lubricant, typically a high viscosity petroleum grease, with passages 
provided to communicate the reservoir with the bearing space between the 
cutter and the journal pin. A compensator in the form of a resilient 
membrane is located in the reservoir with one side of the membrane exposed 
to the lubricant and the other side exposed to the exterior of the rock 
bit. The compensator functions to equalize the pressure on the mud side of 
the seal with the pressure on its lubricant side under varying pressure 
conditions. 
A compensator of the type described is found in U.S. Pat. No. 3,476,195. 
The referenced patent also describes a low pressure relief valve which 
functions to relieve excessive gas pressures in the bit during normal 
drilling. However, during the raising and lowering of the drill bit into 
an existing bore hole, a substantial pressure differential can develop. 
Providing a low pressure relief system would not operate properly because 
the relief valve would open prematurely before deleterious pressure 
differentials are reached. Therefore, too much lubricant would be lost 
during the drill lowering operations. 
Moreover, there are severe limitations as to space in conventional rock 
bits and the amount of space taken up by the relief valve in the 
referenced patent is considered by many as being too much for the safe 
operation of the rock bit. 
SUMMARY OF THE INVENTION 
The present invention obviates the above-mentioned problems by providing a 
lubrication system which incorporates a high pressure relief valve that is 
operable in cases where excessive gas pressures develop. 
In its boradest aspect, the present invention pertains to a sealed bearing 
rock bit having a lubrication system which includes a reservoir and a 
pressure compensator located therein. A high pressure relief arrangement 
is incorporated in the reservoir. The arrangement includes the rubber boot 
utilized as the compensator having an annular valve face which is biased 
against a seat formed in the reservoir wall. 
An advantage of the present invention is that the valve arrangement is 
under a large spring bias. Therefore, the relief system will not open 
during normal operating cycles of the drill. Only when pressure 
differentials in excess of 150 PSI are encountered will the relief system 
be functional. 
Another advantage of the present invention is that the relief arrangement 
is located within existing structure of the rock bit thereby eliminating 
the need for additional structure and bores to house the structure. 
The spring bias acting on the rubber boot comprises a belleville spring 
being urged against the cover cap of the boot. The spring is retained 
within the reservoir by means of a snap ring. 
An advantage of this novel structure is that any internal pressure can be 
vented manually without removing the cap. A slight prying action on the 
cover cap will relieve all pressures. 
As a result a further advantage of the present invention combines a manual 
venting capability with an automatic pressure relief capability without 
requiring any substantial additional space. 
The features of the present invention, which are believed to be novel, are 
set forth with particularity in the appended claims. The present 
invention, both as to its organization and manner of operation, together 
with the further advantages thereof, may best be understood by reference 
to the following description taken in connection with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, FIG. 1 illustrates a three cone rotary rock 
bit, although, the invention can be utilized in other types of rock bits. 
The rotary rock bit, generally indicated by arrow 10, comprises a bit body 
11 having an upper threaded portion 12 for connection to the lower end of 
a rotary drill string (not shown). Extending downwardly from the bit body 
11 are three substantially identical legs 13. The lower end of each of the 
legs is provided with an extended journal pin, details of which will be 
discussed hereinafter. 
A rotary cone cutter 14 is rotatively positioned on each journal pin of a 
respective leg 13. Each cone cutter 14 includes a cutting structure 15 on 
its outer face which is adapted to disintegrate the formations as the bit 
is rotated and moved downward. The cutting structure 15 is shown in the 
form of tungsten carbide inserts, however, it is to be understood that 
other cutting structures such as milled steel teeth formed on the cone 
cutters may be utilized. 
The bit 10 further includes a central passageway 16 extending along the 
center axis of body 11 to allow drilling fluid to enter from the upper 
section of the drill string immediately above and pass downward through 
three jet nozzles 17, one of which is shown in FIG. 1. 
In operation, the drill bit 10 is connected as a lower member of a rotary 
drill string (not shown) and lowered into a well bore until the rotatable 
cone cutter 14 engages the bottom of the well bore. Upon engagement with 
the bottom well bore the drill string is rotated, rotating bit 10 
therewith. Drilling fluid is forced down through the interior passage of 
the rotary drill string and continues through the central passageway 16 of 
the bit 10, passing through the three nozzles 17, past the cutting 
structure 15 of the cutter 14 to the bottom of the well bore, and then 
upwardly into the annulus between the rotary drill string and the wall of 
the well bore carrying with it the cuttings and debris from the drilling 
operations. 
FIG. 2 illustrates the interior structure of one leg 13 of the rock bit 10. 
The leg 13 includes a journal pin 18 extending inwardly for engaging the 
bearing surfaces of the cutter 14. Although several combinations of 
bearing assemblies can be utilized, the system illustrated comprises a 
friction bearing 19, ball bearings 20, a friction bearing 21, and a thrust 
button 22. An annular seal 23 is located at the backface of the cutter 14 
to prevent lubricant from leaking from the bearing area to the exterior of 
the rock bit. 
The lubrication system for each leg 13 comprises a reservoir 24 filled with 
a lubricant communicating with the bearing area via a passageway 25. Other 
passageways (not shown) are located within the journal pin 18 connecting 
passageway 25 with the various bearing assemblies 19, 20, 21 and 22. A 
compensator, commonly referred to as a rubber boot, is located in the 
reservoir 24. The compensator comprises a resilient membrane 26 molded 
around a stiffener sleeve 27. A cover cap 28 is attached to the upper end 
of the membrane 26 and includes passageways 29 for exposing the one side 
of the membrane 26 to the exterior pressures acting on the rock bit 10. 
The other side of the membrane 26 is exposed to the lubricant pressures. 
In order for the seal 23 to function properly, the lubricant pressure 
acting on the seal 23 must be equal to the exterior or mud pressure acting 
on the seal 23. This is accomplished by the pressure compensator described 
above. As the mud pressure increases, the increased mud pressure acts on 
the membrane 26 to compress the lubricant within the lubricant system 
until the lubricant pressure and mud pressure equalize. 
Conventionally, the cover cap 28 is secured within the reservoir 24 by a 
threaded connection. However, this is not followed in the present 
construction. In the present embodiment the cover cap 28, along with the 
membrane 26 and sleeve 27 is floatingly mounted within the reservoir 24 by 
means of a belleville spring 30 which, in turn, is secured by means of a 
snap ring 31 engageable with the wall of the reservoir 24. The belleville 
spring 30 provides the spring bias for the pressure relief system of the 
present invention. 
The pressure relief system further includes a valve seat 32 in the form of 
an annular shoulder formed on the wall of the reservoir 24. The valve seat 
32 functions to receive a valve face 33 formed on the membrane 26. The 
valve face 33 is biasedly urged against the seat 32 by the belleville 
spring 30. The valving arrangement described above functions to relieve 
the excess lubricant pressure generated. This is accomplished when the 
lubricant pressure overcomes the spring force of the belleville spring 30 
to unseat the valve face 33 from the seat 32. In the preferred embodiment, 
the spring pressure on the belleville spring 30 is equal to 150 pounds per 
square inch. 
Beside functioning to relieve excessive lubricant pressures during 
operation, the internal pressures can be manually vented without removing 
the cap 28. This is easily accomplished with a slight prying action on the 
cap 28 to again overcome the bias of the belleville spring 30 to unseat 
the valve face 33. 
It should be noted that various modifications can be made to the assembly 
while still remaining within the purview of the following claims.