Abstract:
A power tong is disclosed for gripping a pipe, the power tong comprising: a frame with a pair of arcuate portions that define both an axial pipe passage and a throat for receiving a pipe laterally into the axial pipe passage; a hydraulic motor for rotating the pipe; a pair of doors for restricting access to the throat, each door mounted to a respective arcuate portion; a valve housing with an inlet port, an outlet port, a fluid chamber, and a valve member, the outlet port being connected to supply hydraulic fluid to the hydraulic motor; and a pair of valve actuators, each valve actuator responsive to the position of a respective door to operate the valve member to reduce fluid pressure through the outlet port when one or both doors are out of a closed position.

Description:
TECHNICAL FIELD 
       [0001]    The document relates to oil drilling, well repair, and workover with power tongs security door guards, especially automatic safety protection devices for open type hydraulic power tongs with double doors. 
       BACKGROUND 
       [0002]    Open type power tongs may incorporate safety devices. Currently there are a variety of safety devices for open type power tongs. An example is China Patent No. 201320611725.5, entitled “One kind of open type hydraulic power tongs gated security apparatus.” The patent discloses a tong with gate valves, shafts, brackets, bracket, pin, safety doors, power tong clamp body, the safety doors connected to the opening of the hydraulic motor hydraulic power tongs; a gating valve, the gating valve connected to the oil inlet and return port of the hydraulic motor; both ends of the shaft end of the shaft of the joint by a pin hinged safety gate, one end fixedly connected to the door control valve spool ends; both ends of the hose connector at one end through the bracket tongs clamp body, one end is fixed to the bracket; bracket and gated valve body fastened into one. This protection structure promotes safe operation of single door hydraulic power tongs. However, this structure is not applicable to the larger openings of double-door hydraulic power tongs. Another example is the Chinese patent No. 200920007413.7, entitled “An opening hydraulic power tong with a safety door automatic protection device”. The patent discloses a tong with a ram-type two-way door or on a secure power tong tongs body change the valve; between the manual valve and the hydraulic motor has a double check valve; security door opening or closing of the control mandrel type two-way valve for the security structure direction. This structure can be used on the double door power tongs but there are several practical problems: 1. because the stop valve is set up between the hand-operated direction valve and the hydraulic motor and it is a double-pilot operated check valve for stopping the oil, the hydraulic system will always build pressure once the door is not closed. 2. the jack-type two-way valve is provided on the security door or tongs clamp body, is easy to crash, and it is through the tubing and dual pilot check valve is connected to a pipeline, so problems may arise when the pipeline is long. Therefore, a new structure is needed for protection devices applied to double-door hydraulic power tongs. 
       SUMMARY 
       [0003]    An opening type hydraulic power tong with a two-gate structure for safe operation of the tong. 
         [0004]    A power tong for gripping a pipe, the power tong comprising: a frame having a pair of arcuate portions that define an axial pipe passage and a side opening for passing a pipe laterally into the axial pipe passage; a pair of doors, each door connected to a respective arcuate portion, the pair of doors having an open position and a closed position, in which the pair of doors restrict access to the side opening when in the closed position; and a part connected to detect the position of the pair of doors and to restrict the operation of the power tong when one or both of the doors are out of the closed position. 
         [0005]    A power tong is disclosed for gripping a pipe, the power tong comprising: a frame with a pair of arcuate portions that define both an axial pipe passage and a throat for receiving a pipe laterally into the axial pipe passage; a hydraulic motor for rotating the pipe; a pair of doors for restricting access to the throat, each door mounted to a respective arcuate portion; a valve housing with a fluid chamber, an inlet port, an outlet port, and a valve member, the outlet port being connected to supply hydraulic fluid to the hydraulic motor; and a pair of valve actuators, each valve actuator responsive to the position of a respective door to operate the valve member to reduce fluid pressure through the outlet port when one or both doors are out of a closed position. 
         [0006]    A power tong for gripping a pipe, the power tong comprising: a frame having a pair of arcuate portions that define an axial pipe passage and a throat for receiving a pipe laterally into the axial pipe passage; a hydraulic motor mounted on the frame for rotating the pipe; a pair of doors, each door mounted to a respective arcuate portion, the pair of doors having an open position and a closed position, in which the pair of doors restrict access to the throat when in the closed position; a valve housing with an inlet port, an outlet port, a pair of valve members, and a fluid chamber connecting the inlet port and the outlet port, the valve housing being connected to supply hydraulic fluid in sequence through the inlet port, the fluid chamber, and the outlet port; and a pair of valve actuators, each valve actuator responsive to the position of a respective door to operate a respective valve member to independently reduce fluid pressure to the outlet port when the respective door is out of the closed position. 
         [0007]    The model provides a double-door gating safety protection device with an opening type hydraulic power tong comprising a gating valve, a push-pull cable system, a bracket, a support, a round pin axle, left and right doors, a power tong body and a hydraulic motor. The left and right doors are installed on the power tong body. There is a gate valve body comprising two gate valve members. The advancing of its hydraulic fluid port and hydraulic motor, oil return opening communicate with each other. There are two push-pull cable systems. One end of each cable system is connected to a different door. The other end of each cable system is connected to the valve body. There may be a model with two flexible axles, and one end of which connects and passes through a round pin axle connected to a door (left or right) and one end of which is connected to the gate valve. One end of each cable may be connected to the power tong body via a support while the other end may be fastened to a bracket, the bracket connected to the gate valve body. The beneficial effects of the model are that the two safe gate devices that open the door of opening power tong are simple more, reliable, and emergency door no. 1 is opened, and push-pull cable flexible axle just drives the off-load of gate valve, and this improves the opening type hydraulic pressure power tong as it protects the operator&#39;s personal safety more reliably. 
         [0008]    A hydraulic power tongs opening with double-doors gated security devices, including gating valve, push-pull cable shaft, bracket, bracket, pin, left and right security door, power tongs clamp body, a hydraulic motor, left right security door installed at the opening of the power tong tongs body, push the cable shaft by a flexible shaft, hose, flexible shaft couplings and hose fittings and is characterized in that: said valve gating by the gating valve body and two gated valve spool, whose port of the hydraulic motor inlet and oil in the return; the push cable for the two shaft ends of a shaft of its hinged joint at one end by a pin on the right security door at one end fixedly connected to one of the spool valve gated end; both ends of the shaft at the other end by a pin joint root is hinged on the left security doors, one end fixedly connected to the control gate valve wherein the other end of the spool section; two ends of the hose push cable shaft joint bracket by the end of the power tong tongs body, one end fixed to the bracket; the bracket and gated valve body fastened into one. 
         [0009]    For existing fields where there are open type power tongs security technology deficiencies, the model provides an opening hydraulic power tongs gated double-door safety device. 
         [0010]    The model provides a technical solution: one opening hydraulic power tongs double door gated security devices, including gating valve, push cable shaft, bracket, bracket, pin, safety doors left and right security door, power tong calipers, hydraulic motors, the left and right security door installed at the opening of the power tong tongs body, push the cable shaft by a flexible shaft, hose, flexible shaft couplings and hose fittings and is characterized in that: said gate valve from the valve body and two gated valve spool, whose port of the hydraulic motor inlet and oil in the return; the push cable for the two shaft ends one of its soft pin connector end of the shaft through the security door hinged on the right, one end fixedly connected to one of the spool valve gated end; both ends of the shaft at the other end by a pin joint root is hinged on the left security doors, one end fixedly connected in gate valve where the other end of the spool; two ends of the hose push cable connector shaft end bracket on the power clamp body through one end fixed to the bracket; the bracket and gated valve body integrally fastened. 
         [0011]    When the left and right safety doors are closed at the same time, the two shafts of the cable system pull both of the gate valve members forward causing oil port P and port A of the valve body to be connected. In addition, port A and port C or D on the hydraulic motor are connected to form a hydraulic circuit allowing the hydraulic system to work properly 
         [0012]    When the left and right safety doors are opened at the same time, the two shafts of the cable system push both of the gate valve members backward and port P and return port O connect allowing hydraulic fluid to flow back to the hydraulic oil tank, which puts the hydraulic system in the unloading state. In this state the hydraulic power tongs cannot operate normally 
         [0013]    When one of the left and right door is opened, the respective gate valve member is pushed backward and the respective port P and respective return port O connect allowing hydraulic fluid to flow back to the hydraulic oil tank, which puts the hydraulic system in the unloading state. In this state the hydraulic power tongs cannot operate normally 
         [0014]    The model has the beneficial effect of opening the doors of the power tong in a more simple and reliable manner. When a door or both doors are in an open position, the cable system drives the gated valve body into the unloading state, which restricts operation of the power tong. This is a significant improvement as it more reliably protects the operator&#39;s safety. 
         [0015]    In various embodiments, there may be included any one or more of the following features: The valve housing comprises a return port connected to bypass the hydraulic motor, in which the valve member diverts flow to the return port when one or both doors are out of the closed position. The valve housing may be a diverter valve. The valve member comprises a pair of valve members, with each valve actuator responsive to the position of a respective door to operate a respective valve member to divert flow to the return port when the respective door is out of the closed position. The valve members restrict flow to the return port when both doors are in the closed position. When one door is out of the closed position and the other door is in the closed position, the inlet port communicates with the outlet port and the return port. When both of the pair of doors are out of the closed position, fluid communication is cut off between the inlet port and the outlet port. Each of the first restriction surfaces and the second restriction surfaces form cylinders in which the first sealing members and second sealing members, respectively, are shaped to reciprocate. Each valve member forms a spool valve. Each valve member forms a gate valve. The valve member comprises a pair of valve members, with each valve actuator responsive to the position of a respective door to operate a respective valve member to reduce fluid pressure through the outlet port when the respective door is out of the closed position. A hydraulic fluid reservoir connected to supply hydraulic fluid to the inlet port of the valve housing, in which the valve housing comprises a return port connecting the hydraulic fluid reservoir to the fluid chamber, and in which the valve members: restrict flow to the return port when both doors are in the closed position; and divert flow to the return port when one or both of the pair of doors are out of the closed position; and in which: when one door is out of the closed position and the other door is in the closed position, the pair of valve members split fluid flow to the outlet port and the return port; and when both of the pair of doors are out of the closed position, the pair of valve members cut off fluid flow to the outlet port. Each valve member has a first sealing member and a second sealing member, and the fluid chamber defines a first zone, a second zone, and a third zone, with the first zone communicating with the inlet port, the second zone communicating with the outlet port, and the third zone communicating with the return port, in which, for each valve member: the first sealing member regulates fluid flow between the first zone and the second zone; the second sealing member regulates fluid flow between the first zone and the third zone; when the respective door is in the closed position, the first sealing member is unseated and the second sealing member is seated; and when the respective door is out of the closed position, the first sealing member is seated and the second sealing member is unseated. The fluid chamber comprises a pair of conduits that each connect the first zone, the second zone, and the third zone, and each valve member is disposed for axial movement within a respective conduit, with each respective conduit forming a first restriction surface for seating the first sealing member, and a second restriction surface for seating the second sealing member. The first restriction surfaces and the second restriction surfaces form cylinders in which the first sealing members and second sealing members are shaped to reciprocate. For each valve member the first sealing member and the second sealing member are coaxial and separated by a stem. Each valve member forms a gate valve. Each valve actuator connects by mechanical linkage to a respective door. Each mechanical linkage comprises a push and pull cable system, such as a power take off cable. Operating the power tong. Closing the pair of doors; and supplying hydraulic fluid through the valve housing to the hydraulic motor to grip and rotate a pipe within the axial pipe passage. 
         [0016]    These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]    Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: 
           [0018]      FIG. 1  is a schematic front view of a power tong; 
           [0019]      FIG. 2  is a sectional view A-A of  FIG. 1 ; 
           [0020]      FIG. 3  is a schematic view of the valve body when both valve member have been pushed backwards (both doors are in the open position); 
           [0021]      FIG. 4  is a schematic view of the valve body when one of the valve members has been pushed backwards (one of the doors is in the open position). 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims. 
         [0023]    Referring to  FIGS. 1, 2, 3 and 4 :  1 , gate valve;  101 , gate control valve body;  102  and  102 ′, gated valve spool (member);  2 , the carriage; and  3 : V, pushing cable shaft;  301 , a flexible shaft;  302 , hose;  303 , shaft joints;  304 , hose fittings;  4 , the bracket;  5 , pin roll;  6 , left safety door;  7 , the right safety door,  8 , power tong body;  9 , the hydraulic motor. 
         [0024]    The model is further described below in conjunction with the accompanying Figures. 
         [0025]    Referring to  FIGS. 1 and 2 , a double-door gated safety device with an opening hydraulic power tong comprising a gating valve  1 , push-pull cable systems (shafts)  3  and  3 ′, bracket  2 , cable support  4 , pin roll  5 , left safety door  6 , the right safety door  7 , power tong body  8  and the hydraulic motor  9  is shown. Left safety door  6  and the right safety door  7  are mounted at the opening of the power tong body  8 . The push-pull cable system may include a pair of power take off cables, such as a pair of solid cables each with a coating or sheath on the outside. The power take off cables may extend from a respective door to the diverter valve, so when the respective door opens the cable pulls the diverter valve open. Push-pull cable shafts  3  and  3 ′ comprises a shaft  301 , hose  302 , flexible shaft connector  303  and hose connector  304  (the part from the connectors  304  to the valve members  102 / 102 ′ forms a valve actuator). Gating valve  1  comprises a gate valve body  101  and gate valve spool  102  and  102 ′ (valve members) composed of the gated valve  1  oil chamber a 1 , a 2  (second zone of fluid chamber) and a communication port A (outlet port), oil chamber p 1 , p 2  (first zone of fluid chamber) and port P (inlet port) communicates the oil chamber o 1 , o 2  (third zone of fluid chamber) O (return port) and communication ports, oil and fuel tank O port communicates gated valve  1  oiling ports P and A are connected to the hydraulic motor  9  via port C, D; one end of each push-pull cable shaft  3  and  3 ′ is connected to a respective connector  303 ; one connector  303  is hinged to the left safety door  6  via a pin roll  5  and the other connector  303  is hinged to the right safety door  7  via another pin roll  5 ; the other ends of the shafts  3  and  3 ′ are connected to the gate valve members  102  and  102 ′; a end of each hose connector  304  is connected to power tong body  8  via support  4  and the other end of each hose connector  304  is connected to bracket  2 ; bracket  2  and gated valve body  101  is are fastened together. 
         [0026]    When both the left safety door  6  and the right safety door  7  are closed, cable shaft  3  and  3 ′ and respective flexible shafts  301  pull the gated valve spool  102  and  102 ′ forwards causing the gated valve body  101  oil progress port P and port A to connect and port A connects to hydraulic motor  9  via port C or D to form a hydraulic circuit. In that state, the hydraulic system works properly. In  FIG. 1  each valve member is disposed in a respective conduit, with left and right piston drums (first and second sealing members) separated by a narrow stem, with the right drums (second sealing members) mating or seating with a corresponding respective cylindrical restriction surfaces or conduits between chambers p 1  and o 1 , and p 2  and o 2 , respectively. 
         [0027]    Referring to  FIG. 3 , when both the left safety door  6  and the right safety door  7  are open, the cable shafts  3  and  3 ′ and respective shafts  301  push gated valve spool  102  and  102 ′ backwards causing gate valve body  101  return ports P and O to connect, which allows hydraulic fluid to flow to the hydraulic oil tank. In that state, the hydraulic system is in the unloading state and the hydraulic power tongs cannot operate normally. In  FIG. 3  the left drums mate or seat with corresponding respective cylindrical restriction surfaces or conduits between chambers a 1  and p 1  and a 2  and p 2 , respectively. 
         [0028]    As shown in  FIG. 4 , when one either the left safety door  6  or the right safety door  7  is in the open position, the respective pushing cable shaft  3  or  3 ′ and the respective shaft  301  wherein a push gated valve spool  102  or  102 ′ after the shift in this case motivated gated valve body  101  ports P, A and back to the oil port O port communicates directly back to the hydraulic oil tank, hydraulic system in the unloading state, hydraulic power tongs cannot operate normally. 
         [0029]    In some cases the tong is a back up tong, or used in association with a back up tong. In some cases the frame of the tong is connected to a backup tong. In some cases the doors open and close via a sliding or swinging motion. The valve housing need not have a return port, and may restrict or cut off the flow through the outlet port when one or both doors are out of the closed position. In such cases a system may be employed to avoid damage to the hydraulic system, such as the pump, when the valve housing closes or cuts off flow in the supply line. For example a sensor may be employed to detect increasing back pressure upstream of the valve housing, and in response may shut off the hydraulic pump or shunt hydraulic fluid back to the hydraulic reservoir. In some cases the valve actuators are operated via a hydraulic system, or another suitable system such as a servo system. In some cases the position of each door is detected by a respective sensor, which is connected to relay signals to be used to control the valve actuators. The sensor may be a wireless sensor. 
         [0030]    Reducing fluid pressure may include decreasing to a non-zero flow, or cutting off the fluid flow entirely. The return port may be connected via a circuit back to the reservoir, the circuit being unloaded relative to the connection between the motor and valve housing, such that fluid flows preferentially through the unloaded circuit back to the reservoir. The valve actuators may be connected to operate together. The cables may be spring loaded or otherwise tensioned to return to initial positions. The valve member may be a single spool valve. Seating refers to the function of restricting or blocking fluid flow. The closed position includes a fully closed position. The motor may be mounted to the tong body or frame. The doors cooperate to block the opening, and may have a latch or lock at the tips to secure the doors in place. The safety device may operate other than by shutting off the hydraulic motor. The safety device may initiate a warning indicator, such as a light or alarm, or may cause a reduction but not termination in motor action. The device may operate a mechanical linkage to control the motor. The out of closed position may include a fully open position. 
         [0031]    Translation of Chinese non-provisional patent serial no. 204920850 shown below. 
       A Double-Door Gating Safety Protection Device with an Opening Hydraulic Power Tong 
       [0032]    A double-door gating safety protection device with an opening hydraulic power tong covers gating valve, push-and-pull flexible axle, bracket, support, pin roll, left and right safety doors, power tong body and hydraulic motor. The left and right safety doors are installed in the opening of the power tong body; the gating valve consists of gating valve body and two gating valve elements, whose oil port is connected to oil inlet and return port of hydraulic motor; there are two push-and-pull flexible axles, between which one end of the joint of both ends of one axle is hinged to the left or right safety door via the pin roll and the other end is fixedly connected to one end of the gating valve element; one end of the joint of both ends is fixed to the power tong body via the support and the other end is fixed on the bracket; the bracket and the gating valve body are fastened together. The beneficial effect of this utility model is that the double-door safety gating device with an opening power tong is simpler and more reliable. Once both safety doors are opened or either safety door is opened, the push-and-pull flexible axle drives the gating valve for unloading, and thus the safety performance of the opening hydraulic power is tong remarkably improved so as to protect the personal safety of operators more reliably. 
         [0033]    This utility model safety protection device involving power tong for petroleum drilling and well repair, especially, the double-door gating safety protection device with an opening hydraulic power tong, belongs to the mechanical safety protection technology for oil field. 
         [0034]    Due to the safety needed, the opening hydraulic tong for oil field is required to be equipped with safety protection devices. At present, the opening hydraulic tong has been improved for several times and now can provide multiple forms of safety protection. For example, the patent for utility models named “A gating safety protection device with an opening hydraulic power tong” with the Chinese patent No. 201320611725.5 published a gating safety device with an opening hydraulic power tong consisting of gating valve, flexible axle, bracket, support, safety doors, power tong body and hydraulic motor, of which the safety doors are installed in the opening of the power tong body; oil port of gating valve is connected to the oil inlet and return port of the hydraulic motor; one end of the flexible joint of both ends of one flexible axle is hinged to the safety door via the pin roll and the other end is connected to the end of gating valve element, while one end of the flexible joint of both ends of the other flexible axle is fixed on the power tong body via the support and the other end is fixed on the bracket; the bracket and the gating valve body are fastened together. The safety protection structure can produce great protective effect for the single-door opening hydraulic power tong, but not for the double-door opening hydraulic power tong with a larger opening. For another example, the patent for utility models named “A safety door automatic protection device with an opening hydraulic power tong” with the Chinese patent No. 200920007413.7 punished a safety protection structure for which the post-rod two-position three way reversing valve is set upon the safety door or the hydraulic power tong body; double-pilot operated check valve is set up between the hand-operated direction valve and the hydraulic motor; the opening or closing of safety door controls the reversing of the post-rod two-position three way reversing valve. The structure can be used for double door, but shows the following problems in actual utilization: 1. the stop valve is set up between the hand-operated direction valve and the hydraulic motor and it is a double-pilot operated check valve to stop the oil, so the hydraulic system will always build the pressure once the door is not closed; 2. the post-rod two-position three way reversing valve is set up on the safety door or the hydraulic power tong, causing that it is easily damaged, and it is connected to the double-pilot operated check valve via the oil pipe, so problems may be caused due to too long pipe. Therefore, a new structure is needed for the double-door safety protection device with an opening hydraulic power tong for oil field pipe. 
         [0035]    The utility model provides a double-door gating safety protection device with an opening hydraulic power tong regarding the deficiencies in the safety protection technology of opening hydraulic power tong for oil field pipes. 
         [0036]    The technical proposal of the utility model is a double-door gating safety protection device with an opening hydraulic power tong consisting of gating valve, push-and-pull flexible axle, bracket, support, pin axle, left safety door, right safety door, power tong body and hydraulic motor. The left and right safety doors are installed in the opening of the power tong body and the said push-and-pull flexible axle is composed of flexible axle, flexible pipe, flexible axle joint and flexible pipe joint and is featured with that the said gating valve is composed of gating valve body and two gating valve elements, with the oil port connected to the oil inlet and the return port of the hydraulic motor; there are two push-and-pull flexible axles, between which one end of the flexible axle joint of both ends of one flexible axle is hinged to the right safety door via the pin roll and the other end is firmly connected to the end of one gating valve element; one end of the flexible axle joint of both ends of the other flexible axle is connected to the left safety door via the pin roll and the other end is firmly connected to the end of the other gating valve element; one end of flexible axle joint of both ends of two push-and-pull flexible axles is fixed to the hydraulic power tong via the support and the other end is fixed on the bracket; the said bracket and gating valve body are fastened together. 
         [0037]    When left and right safety doors are closed at the same time, the flexible axles in two push-and-pull flexible axles pull elements of two gating valves forward, then oil inlet P and oil inlet A are connected in the gating valve body and oil port A and oil port C or D on the hydraulic motor are connected, and thus an oil hydraulic circuit is formed and the hydraulic system operates normally; when the left and right safety doors are opened at the same time, flexible axles in two push-and-pull flexible axles pull elements of two gating valves backward, then oil inlet P and return port O in the gating valve body are connected and hydraulic oil flows back to the oil tank directly so that the hydraulic system is under the unloading condition, thus resulting in abnormal operation of the hydraulic power tong; when either the left safety door or the right safety door is opened, the opened safety door drives the flexible axle in the push-and-pull axle to move the gating valve element backward, and then oil inlet P, oil inlet A and return port O are all connected and hydraulic oil directly flows back to the oil tank so that the hydraulic system is under the unloading condition, thus resulting in abnormal operation of the hydraulic power tong. 
         [0038]    The beneficial effect of this utility model is that the safety gating device with an opening power tong is simpler and more reliable. Once the safety doors are opened or either safety door is opened, the push-and-pull flexible axle will drive the gating valve for unloading, and thus the safety performance of the opening hydraulic power tong can be improved remarkably so as to protect the personal safety of operators more reliably. 
         [0039]    1. A double-door gating safety protection device with an opening hydraulic power tong covers a gating valve, push-and-pull flexible axle, bracket, support, pin roll, left safety door, right safety door, power tong body and hydraulic motor. The left and right safety doors are installed in the opening of the hydraulic power tong body and the said push-and-pull flexible axle consists of flexible axle, flexible pipe, flexible axle joint and flexible pipe joint with the following features: 
         [0040]    The said gating valve is composed of gating valve body and two gating valve elements, with the oil port connected to the oil inlet and the return port of the hydraulic motor; 
         [0041]    Regarding the gating valve, inner oil chamber a 1  and inner oil chamber a 2  are connected to oil port A, oil chamber p 1  and oil chamber p 2  are connected to oil port P, and oil chamber o 1  and oil chamber o 2  are connected to oil port O. 
         [0042]    There are two push-and-pull flexible axles, between which one end of the flexible axle joint of both ends of one flexible axle is connected to the right safety door via the pin roll and the other end is firmly connected to the end of a valve element of gating valve; one end of the flexible axle joint of both ends of the other flexible axle is connected to the left safety door via the pin roll and the other end is firmly connected to the end of the other valve element of the gating valve; one end of flexible axle joint of both ends of two push-and-pull flexible axles is fixed to the hydraulic power tong via the support and the other end is fixed on the bracket; 
         [0043]    The said bracket and gating valve body are fastened together. 
         [0044]      FIG. 1  is the front structure diagram of the utility model; 
         [0045]      FIG. 2  is the A-A section of  FIG. 1 ; 
         [0046]      FIG. 3  is the diagram of two gating valve elements which move backward; 
         [0047]      FIG. 4  is the diagram of any gating valve element which moves backward. 
         [0048]    Among  FIGS. 1, 2, 3 and 4 :  1 . gating valve;  101 . gating valve body;  102  and  102 ′. element of gating valve;  2 . bracket;  3  and  3 ′. push-and-pull flexible axle;  301 . flexible axle;  302 . flexible pipe;  303 . flexible axle joint;  304 . flexible pipe joint;  4 . support;  5 . Pin roll;  6 . left safety door;  7 . right safety door;  8 . power tong body;  9 . hydraulic motor 
       Specific Mode of Execution 
       [0049]    Here are the further descriptions of the utility model in combination with the drawings and examples. 
         [0050]    As shown in  FIGS. 1 and 2 , a double-door gating safety protection device with an opening hydraulic power tong consists of gating valve  1 , push-and-pull flexible axles  3  and  3 ′, bracket  2 , support  4 , pin roll  5 , left safety door  6 , right safety door  7 , power tong body  8  and hydraulic motor  9 . Left safety door  6  and right safety door  7  are installed in the opening of the power tong body  8 ; push-and-pull flexible axle  3  and  3 ′ is composed of flexible axle  301 , flexible pipe  302 , flexible axle joint  303  and flexible pipe joint  304 ; the gating valve  1  is composed of the gating valve body  101  and gating valve elements  102  and  102 ′, in which oil chamber a 1  and a 2  are connected to oil port A, oil chamber p 1  and p 2  are connected to oil port, oil chamber o 1  and o 2  are connected to oil port O, oil port O is connected to the oil tank, and oil port P and oil port A in the gating valve are connected to oil inlet C and return port D in the hydraulic motor; one end of flexible axle joint  303  on both ends of push-and-pull flexible axles  3  and  3 ′ is hinged to left safety door  6  and right safety door  7  via pin roll  5 , while the other end is firmly connected to the ends of gating valve elements  102  and  102 ′; one end of flexible pipe joint  304  of both ends is fixed to power tong  8 , while the other end is fixed to bracket  2 ; bracket  2  and gating valve body  101  are fastened together. 
         [0051]    When left safety door  6  and right safety door  7  are both closed, flexible axle  301  in push-and-pull axles  3  and  3 ′ pulls gating valve elements  102  and  102 ′ forward, then oil inlet P in gating valve body  101  is connected to oil port A and oil port A is connected to oil port C or D in hydraulic motor  9 , thus a hydraulic circuit is formed so that the hydraulic system can normally operate. 
         [0052]    As shown in  FIG. 3 , when left safety door  6  and right safety door  7  are both opened, flexible axle  301  in push-and-pull axles  3  and  3 ′ pulls gating valve elements  102  and  102 ′ backward, then oil inlet P in gating valve body  101  is connected to oil port O and hydraulic oil directly flows back to the oil tank, thus the hydraulic system is under the unloading state, resulting in abnormal operation of the hydraulic power tong. 
         [0053]    As shown in  FIG. 4 , when either safety door  6  or right safety door  7  is opened, one of flexible axle  301  in push-and-pull axles  3  and  3 ′ pulls gating valve elements  102  and  102 ′ backward, then oil inlet P, oil port A and oil port O are connected in gating valve body and hydraulic oil directly flows back to the oil tank, thus the hydraulic system is under the unloading state, resulting in abnormal operation of the hydraulic power tong.