In the pump-pipeline system, the inlet and outlet pipelines of the pump are subjected to complex mechanical loads: displacement caused by thermal expansion, vibration caused by pump operation, and blind plate force caused by internal pressure. If these loads act directly on the pump body, it will lead to deformation of the pump housing, bearing damage and even interface leakage. The function of the pump outlet flue expansion joint is this-as a flexible connecting element between the pump and the pipeline, it can effectively isolate the above-mentioned harmful loads and protect the safe operation of pump equipment. This paper will systematically analyze the four core functions and engineering application points of the pump outlet flue expansion joint.
1. Absorb thermal expansion and eliminate pipeline thermal stress
The medium in the pump outlet line, such as water, flue gas, or chemical fluid, may change significantly in temperature during delivery. Taking a pump in a thermal system as an example, the outlet pipe temperature can rise from normal temperature to hundreds of degrees, resulting in considerable thermal expansion displacement.
The primary embodiment of the function of the pump outlet flue expansion joint is to absorb this thermal expansion. Install universal expansion joints on the inlet and outlet pipelines of the pump, which can compensate the thermal expansion of the pipeline and reduce the thrust of the pipeline thermal expansion to the pump。 The expansion joint takes advantage of the effective expansion and contraction deformation of its bellows to absorb the dimensional change of the pipeline caused by thermal expansion and contraction, so as to reduce the stress on the pipe wall and the force acting on the pump body。
If the expansion joint is not provided, the huge thrust generated by thermal expansion will directly act on the pump body interface, which may lead to deformation of the pump housing, flange leakage and even pipeline cracking. This is the fundamental reason why the pump outlet must be provided with an expansion joint.
2. Isolate mechanical vibration and protect pump body and pipeline
Pumps generate constant mechanical vibrations when they are in operation, especially centrifugal and reciprocating pumps. If these vibrations are transmitted through rigid pipelines, they will not only accelerate the fatigue of pipeline welds, but also react to the pump body and affect its operating stability.
The function of flue expansion joint at pump outlet is outstanding in vibration reduction. The expansion joint is applied to the pump inlet and outlet pipeline as a flexible linkage, which can absorb the vibration generated by pump operation。 Using the effective expansion and contraction deformation of the bellows, the expansion joint can absorb the vibration of equipment and reduce the influence of the vibration of equipment on the pipeline。
This role is particularly important for high-speed pumps (such as boiler feed water pumps and chemical process pumps). By installing the expansion joint at the pump inlet and outlet, the vibration transmission can be effectively isolated, which not only protects the pipeline system, but also avoids the damage to the bearing and mechanical seal of the pump itself caused by vibration feedback。
3. Eliminate the blind plate force and improve the stress condition of equipment
"Blind plate force" is a problem that is often neglected but has serious consequences in the design of pipeline system. When there are flexible joints in the pipeline and there is a blind plate downstream (such as the valve closed state or the equipment interface), the internal pressure will generate a huge thrust at the blind plate end, which will make the pipeline move toward the blind plate. This thrust is the blind plate force.
One of the key functions of the pump outlet flue expansion joint is to eliminate or reduce the influence of blind plate force on the pump. The bending force balance type expansion energy saving makes the equipment not be affected by the blind plate force generated by internal pressure, improves the stress condition of the equipment, and makes the equipment easy to fix。
On the outlet pipeline of the pump, when the outlet valve is suddenly closed, the blind plate force generated by the internal pressure will violently impact the pump body. The correct use of expansion joints (especially models with limiting devices) can transmit the blind plate force to other parts of the pipeline and avoid the impact force caused by the concentration of thrust on the proximal end of the pump to damage the equipment。
4. Compensate for installation errors and facilitate pipeline connection
In the field installation, there is inevitable axial deviation, angular deviation or spacing error between the pump interface and the pipeline flange. Forced connections create additional assembly stresses that act on the pump body for a long time.
The function of the pump outlet flue expansion joint also includes compensating for installation errors. The expansion joint can compensate the axial, transverse and angular cold and hot deformation of the absorption pipeline, and its expansion and contraction amount also facilitates the installation and disassembly of the valve pipeline。 This effect makes the connection between the pump and the pipeline more flexible, reduces the installation accuracy requirements and improves the construction efficiency.
V. Expansion joint type selection guide
For pump outlet operating conditions, the appropriate expansion joint type should be selected according to media characteristics and operating parameters:
Suggestions for selection:
- Metal corrugated expansion joints are preferred for pump outlets that transport high-temperature flue gas or hot oil
- For water pump, circulating water pump and other normal temperature working conditions, rubber expansion joint is more cost-effective
- For chemical pumps with strong corrosive media, fluorine-lined or all-PTFE expansion joints can be selected
VI. Installation precautions
In order to ensure that the function of the flue expansion joint at the pump outlet is fully exerted, attention should be paid to:
- Installation near pump outlet: Expansion joint should be as close to pump outlet flange as possible to protect pump body to the maximum extent
- Set limiting device: For working conditions that may generate large blind plate force, the expansion joint with limiting tie rod should be selected
- Avoid twisted installation: The expansion joint shall be kept in a natural state and shall not be forcibly twisted to accommodate pipe deviations
- Guide bracket matching: Set guide bracket at appropriate position downstream of the expansion joint to ensure the expansion and contraction direction
- Pre-compression treatment: For high temperature conditions, cold pre-compression shall be carried out as designed during installation
VII. SUMMARY
The function of pump outlet flue expansion joint can be summarized as four cores: absorbing thermal expansion to eliminate thermal stress of pipeline, isolating vibration to protect pump body and pipeline, eliminating blind plate force to improve the stress condition of equipment, and compensating installation error to facilitate pipeline connection. These four functions are interrelated to ensure the safe and stable operation of the pump-pipeline system.
In engineering practice, the type of expansion joint (metal/rubber/non-metal) should be selected scientifically according to the requirements of medium temperature, pressure, corrosivity and vibration, and the installation specifications should be strictly followed. The function of pump outlet expansion joint can effectively prolong the service life of pump equipment and reduce the failure rate of pipeline system. It is an indispensable key link in the design of pump station and industrial pipeline.