Product Introduction of Small Pull rod
The small pull rod is a dedicated tensioning accessory in the hydraulic end installation and connection system of the plunger pump. It is usually used in conjunction with the large pull rod, pump head body, connection seat and corresponding nuts, etc., to tighten, connect and maintain the position of the local structure of the hydraulic end.
In some three-cylinder plunger pump structures, the small pull rod and the large pull rod are installed as independent parts of different specifications simultaneously in the hydraulic end assembly. Although both belong to the category of tie rod load-bearing components, their installation positions, lengths, thread specifications, and specific connection positions they undertake are not the same. Therefore, they cannot be simply interchanged.
The small pull rods are usually short in length and mainly matched according to the pump head body and the corresponding installation structure. They maintain the stability of related components through threaded connection and pre-tightening, and together with other pull rods, ensure the overall connection state of the hydraulic end during operation.
The main function of the small pull rod
1. Local connection at the hydraulic end: The small pull rod is used to connect the pump head body with the corresponding installation part, and together with other pull rods, it forms a fixed structure at the hydraulic end.
2. Provide axial tension force: Through the end threads and the matching nuts, a pre-tightening effect is generated to keep the connection parts in the specified assembly state.
3. Maintain installation position: Work together with the large tie rod and other fasteners to restrict abnormal displacement of the hydraulic end components and maintain the relative position of the pump head body and the connecting structure.
4. Share the cyclic load: During the operation of the plunger pump, the hydraulic end is subjected to periodic pressure changes and vibrations, and the small pull rod needs to bear repeated tensile loads at the corresponding connection position.
5. Facilitates disassembly and assembly of the hydraulic end: When the hydraulic end assembly is under maintenance or replacement, the pump head and adjacent connecting components can be disassembled by removing the small pull rod and related nuts.
The difference from the large pull rod
Small pull rods and large pull rods are used simultaneously in some plunger pumps, but they belong to two different specifications and installation positions of parts.
Large tie rods usually undertake the main overall connection function of the hydraulic end, and the length of the rod body and the load-bearing span are relatively large. The small pull rod is more often used at the local or lower connection position of the hydraulic end. Its length, installation space and end connection form are determined according to the structure of the pump head.
Therefore, when making a purchase, one should not merely judge the size based on the names of "large pull rods and small pull rods", but should verify it in combination with the pump model, part number and actual installation position.
The difference from a plunger rod
The small pull rod is a hydraulic end fixed connection component. During normal operation, it does not move back and forth along with the plunger by itself. The plunger rod or crosshead pull rod belongs to the motion transmission mechanism and is used to drive the plunger to reciprocate.
Therefore, the key points for selecting a small pull rod are the installation position, the length of the pull rod, the threads at both ends and the pre-tightening connection relationship, rather than the diameter of the plunger and the reciprocating stroke itself.
Structural features
Short tie rod structure: Compared with large tie rods, small tie rods usually have a shorter connection length and are suitable for local installation positions at the hydraulic end.
End thread connection: One or both ends are usually provided with connection threads to form a mechanical connection with the pump head body, connection seat or matching nut.
Withstand tensile and pre-tightening loads: After installation, it is necessary to maintain a stable axial pre-tightening state and withstand the cyclic tensile forces generated during operation.
The specification specificity is relatively strong: The small pull rods of different pump types may vary in length, rod diameter, thread and end structure. Generally, they should be matched according to the part number or technical drawing.
Common examination areas
During maintenance, special attention should be paid to inspecting the threads at both ends of the small pull rod, the root of the threads, the transition area of the rod body, and the position in contact with the nut. Observe whether there are any thread scratches, corrosion, bending, deformation or surface cracks.
If the corresponding connection position of the small pull rod repeatedly becomes loose, the pre-tightening state of the matching nuts, washers, installation end faces and other pull rods should be checked simultaneously to identify whether there is uneven local force distribution.
For plunger pumps that operate under high-pressure and high-frequency reciprocating conditions for a long time, attention should also be paid to the fatigue damage at the root of the pull rod thread and the diameter transition part.
Key points for selection
The small pull rod is a special connecting part for the hydraulic end 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. The specific installation position of the small pull rod;
3. Original part number;
4. Total length of the pull rod;
5. Rod diameter;
6. The diameters and pitches of the threads at both ends;
7. Effective thread lengths at both ends;
8. Are there any steps, positioning shoulders or special end structures?
9. Specifications of matching nuts and washers;
10. Materials and fastening requirements specified in the original equipment.
Installation and Maintenance
Before installation, the rod body and the threads at both ends of the small pull rod should be inspected. The threads, nuts and installation contact surfaces should be cleaned to ensure there are no obvious bumps, corrosion, cracks or thread damage.
When multiple pull rods are simultaneously involved in the connection of the hydraulic end, they should be tightened step by step in the sequence specified for the corresponding pump type to avoid one pull rod being fully locked in advance, which may cause the pump head to be installed at an Angle or the preload of each pull rod to be uneven.
The tightening torque of the small pull rod nut, the pre-tightening method and whether an anti-loosening structure is needed should be carried out in accordance with the corresponding plunger pump maintenance manual or technical drawings. It is not advisable to use uniform empirical values to replace the original equipment requirements.
Procurement Instructions
Juli Petroleum Drilling and Production Equipment Co., Ltd. provides small pull rods and related connection accessories for the hydraulic end of plunger pumps. The small pull rods of different pump types may vary in total length, rod diameter, thread, installation position and end structure. When purchasing, it is recommended to provide the pump model, original part number, physical dimensions or technical drawings to accurately verify the product.