Product Introduction of Large Pull rod
The large pull rod is an important load-bearing connection component between the power end and the hydraulic end of the plunger pump. It is usually arranged along the axial direction of the pump body. Through the pull rod thread, nut and related positioning structure, the hydraulic end assembly is reliably connected to the power end frame.
When a plunger pump is in operation, the power end converts rotational motion into the reciprocating motion of the plunger, while the hydraulic end bears the pressure of the medium and completes the suction and discharge processes. The large tie rod is connected between the power end and the hydraulic end. It is necessary to maintain a stable assembly relationship between the two major assemblies under the action of periodic pressure loads, mechanical vibrations and reciprocating loads of the plunger.
Therefore, the large pull rod is not an ordinary installation screw. Its diameter, effective length, threads at both ends, material properties, pre-tightening state during installation, and the fit with the pull rod nut all directly affect the fixed state of the hydraulic end and the reliability of the entire pump structure.
The main function of the large pull rod
1. Connect the power end and the hydraulic end: The core function of the large pull rod is to fix the hydraulic end of the plunger pump at the power end or the connection position of the frame, so that the two main assemblies form a stable integral structure.
2. Withstand axial tensile loads: When the hydraulic end of a plunger pump is in operation, the internal pressure changes periodically, generating a significant alternating force at the connection point of the hydraulic end. The large tie rod constrains and transmits these axial loads through pre-tightening and its own load-bearing capacity.
3. Maintain the installation position of the hydraulic end: Multiple large tie rods working together help maintain the correct distance and relative position between the hydraulic end and the power end, preventing abnormal displacement of the hydraulic end during operation.
4. Maintain the centering relationship of the plunger system: The stable installation position of the hydraulic end is an important foundation for maintaining a reasonable axial relationship among components such as the plunger, packing box, and power end cross head. Abnormal installation status of the pull rod may further affect the working condition of the reciprocating components of the plunger.
5. Facilitate the disassembly and assembly of the hydraulic end assembly: When the hydraulic end of the plunger pump undergoes major overhauls or the assembly is replaced, the hydraulic end and the power end can be separated by removing the pull rod nut and related connecting parts.
Installation position and force relationship
The large pull rod is usually arranged between the power end and the hydraulic end of the plunger pump. One end is in coordination with the power end frame or the corresponding fixed structure, while the other end passes through or connects to the installation position of the hydraulic end, and is then locked by the pull rod nut.
Multiple tie rods need to be jointly maintained in the specified pre-tightened state. If the tightness of each pull rod varies greatly, it may cause uneven force distribution at the hydraulic end, resulting in individual pull rods bearing excessive cyclic loads. Therefore, during installation, not only should the specified fastening requirements be met, but also the uniformity among multiple tie rods should be noted.
The difference from a plunger rod
Although both the large pull rod and the plunger rod have the word "rod" in their names, their functions are completely different.
The large pull rod is a connecting part of the pump body structure, mainly connecting the power end and the hydraulic end. During normal operation, it does not move back and forth along with the plunger by itself. The plunger rod belongs to the reciprocating transmission system and is used to transfer the movement of the crosshead to the plunger.
Therefore, the key points for selecting large tie rods are the length, diameter, threads at both ends and the pre-tightening connection structure of the tie rod, while for plunger rods, more attention is paid to the reciprocating connection end, the connection method of the plunger and the guiding fit.
Product structure characteristics
Long rod load-bearing structure: Large tension rods usually have a relatively large axial length, spanning the hydraulic end and the power end, with the middle rod part bearing the main tensile load.
Connection structure at both ends: Depending on the pump type, one or both ends of the pull rod can be designed with threads to form a connection with the frame, hydraulic end and pull rod nut.
It is necessary to maintain the specified preload: The large pull rod keeps the hydraulic end stable through correct preload. Its installation effect not only depends on the rod body itself, but also is related to the nut, gasket, contact surface and fastening process.
Subjected to periodic loads: During the long-term operation of the high-pressure plunger pump, the large pull rod continuously bears alternating tensile loads and vibrations. Therefore, the root of the thread, the transition point of the rod diameter, and the contact end face are key inspection areas.
Common failures and inspection sites
When inspecting the large pull rod, special attention should be paid to checking the threads at both ends, the transition area between the threads and the smooth rod, the surface of the rod body, and the contact position of the nut. Observe whether there are any thread scratches, corrosion, pitting, bending, surface cracks or abnormal wear.
Under high-load and high-pressure conditions, repeated cyclic force application may cause fatigue damage at the local stress concentration points of the tie rods. If cracks, obvious plastic deformation or severe damage to the thread are found, it is not advisable to continue using it as a common repairable fastener.
If a certain pull rod or pull rod nut repeatedly becomes loose, it is also necessary to simultaneously check the installation surfaces of the hydraulic end and the power end, the pull rod nut, the gasket and the tightness of other pull rods, and investigate whether there is uneven force or abnormal assembly surfaces.
Key points for selection
The large pull rod is a major load-bearing connection component of the plunger pump. When purchasing, it is recommended to focus on confirming the following information:
1. Brand, series and specific model of plunger pump;
2. Power end and hydraulic end models;
3. Total length of the large pull rod;
4. Diameter of the pull rod body;
5. The diameter, pitch and length of the threads at both ends;
6. Whether the structures at both ends are the same;
7. Specifications of the matching pull rod nuts and washers;
8. Material, strength and heat treatment requirements specified for the equipment;
9. The pre-tightening or fastening requirements specified by the original factory;
10. Original part number, physical sample or technical drawing.
Installation and Maintenance
Before installation, the rod body and the threads at both ends of the pull rod should be inspected. Clean the threads, nuts and installation contact surfaces to ensure there are no cracks, severe corrosion, scratches or thread deformation.
After the hydraulic end is installed in place, the multiple large pull rods should be tightened step by step in accordance with the sequence and method specified for the corresponding pump type to avoid a single pull rod being completely locked at one time, which may cause the hydraulic end to be skewed or unevenly pretightened.
The tightening torque of the pull rod nut, the hydraulic tension value or other pre-tightening methods should be carried out in accordance with the maintenance specifications of the corresponding pump type manufacturer. The diameters, materials and thread structures of pull rods of different specifications vary. It is not advisable to set a uniform universal tightening torque on the web page.
After the plunger pump has been operating at high load for a certain period of time, the condition of the large tie rod and the tie rod nut should be checked in accordance with the equipment maintenance requirements. For equipment with heavy working conditions such as high-pressure fracturing pumps, the pull rods are load-bearing components that need to be inspected regularly and with emphasis.
Procurement Instructions
Juli Petroleum Drilling and Production Equipment Co., Ltd. provides related accessories for the connection of the power end and hydraulic end of large pull rods and plunger pumps. The large pull rods of different pump types may have significant differences in length, rod diameter, threads at both ends, material grade and installation pre-tightening requirements. When purchasing, it is recommended to provide the pump model, power end and hydraulic end models, original part number, physical dimensions or technical drawings to accurately verify the products.