Method for designing diameters of unloader spring and actuating mechanism piston of multi-stage reciprocating compressor

Abstract

The invention relates to a method for designing diameters of an unloader spring and an actuating mechanism piston of a multistage reciprocating compressor. The method comprises the following steps: (1) acquiring air inlet pressure of each stage of a unit; 2) calculating the spring stiffness and the piston diameter of the actuating mechanism; and 3) structural design of an unloader spring. The invention aims to solve the problems that in an existing patent, design for springs and pistons of unloaders of multi-stage reciprocating compressors is lacked, design allowance is prone to occurring in a certain stage or multiple stages, then obvious differences exist in actions of executing mechanisms of all stages, the action performance of the executing mechanisms is poor, and even safety problems occur. On the basis of the underdetermined equation set, the limiting conditions of the piston and the pre-compression amount are combined, parameter matching of all stages is completed, the action consistency of all stages of executing mechanisms is good, the action synchronism of all stages of executing mechanisms is good, and the reliability, stability and safety of a reciprocating compressor stepless air flow adjusting system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of mechanical engineering and compressor technology, specifically a design method for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor. Background Technology

[0002] The continuously variable air volume (CVV) regulation system for reciprocating compressors is one of the core technologies for industrial energy-saving retrofitting. By adjusting the exhaust volume in real time to match actual demand, it significantly reduces energy consumption. The unloader spring and piston, as key components of the actuator, have design parameters that determine the actuator's performance and system safety. Existing patents mainly focus on CVV regulation systems, control methods, and actuators for reciprocating compressors. However, there is limited research on the design optimization of spring and piston diameters at each stage in multi-stage reciprocating compressors. This can lead to problems in practical applications such as inconsistent performance, high noise, and incomplete operation, affecting the system's reliability and stability.

[0003] As key components of the actuator, the unloading spring and piston determine the actuator's performance and system safety through their design parameters. Existing patents primarily focus on reciprocating compressor stepless air volume regulation systems, control methods, and actuators. While patent CN110206712A solves for spring stiffness and design using motion equations, it doesn't consider multi-stage spring and piston design. Since multi-stage reciprocating compressor stepless air volume regulation systems use the same oil pressure, designing the parameters of each stage of the spring and piston to ensure the same oil pressure applies to each stage of the actuator is crucial. Mismatched parameters at any stage can lead to poor actuator performance, such as excessive noise or incomplete movement. A search revealed a temperature control design method for a heavy-duty truck cab shock absorber, published on August 24, 2021, with publication number CN109973584B. This patent optimizes the shock absorber's heat generation and mechanical energy absorption capabilities by increasing the diameter of the spring steel wire and piston rod, thereby controlling its operating temperature within a reasonable range. However, this technical solution mainly focuses on the spring and piston design of single-stage shock absorbers and does not consider the parameter matching problem between different stages in a multi-stage system. Furthermore, the optimization of hydraulic oil flow area using this method is only applicable to specific working conditions and is difficult to directly apply to the complex working conditions of multi-stage reciprocating compressors. This may lead to differences in the action performance of each stage of the actuator, and even cause safety issues.

[0004] A search revealed an improved structure and usage method for a hand-operated micro-sprayer, publication number CN101875034B, published on December 28, 2011. This patent improves the sprayer's adaptability to high-viscosity liquids by optimizing the cooperation between the piston, valve needle, and spring. However, this technical solution only involves the pressure difference design of a single sealed chamber and does not consider the consistency of pressure transmission at each stage in a multi-stage system. Furthermore, the piston and spring design in this patent is mainly designed for low-load, short-stroke applications. If directly applied to the high-pressure, high-frequency conditions of a multi-stage reciprocating compressor, insufficient design margin may lead to decreased performance, such as excessive noise or incomplete operation. These issues indicate that existing technical solutions have significant shortcomings in the design optimization of springs and pistons at each stage in multi-stage systems, especially in parameter matching, operational consistency, and adaptability to complex operating conditions. Therefore, this invention provides a design method for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor, aiming to improve the consistency of action of each stage of the actuator through scientific and reasonable parameter design, thereby enhancing the reliability, stability and safety of the system and meeting the needs of modern industry for high-efficiency and energy-saving equipment.

[0005] The lack of design for unloading springs and pistons in existing patents for multi-stage reciprocating compressors means that there is a design margin in one or more stages, which leads to significant differences in the action of each stage of the actuator, resulting in poor actuator performance and even safety issues. Summary of the Invention

[0006] The purpose of this application is to provide a design method for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor. This addresses the lack of design for the unloader spring and piston in existing patents for multi-stage reciprocating compressors, which can lead to design margins in one or more stages, resulting in significant differences in the action of each stage of the actuator, poor actuator performance, and even safety issues.

[0007] Includes the following steps: 1) Obtain the intake pressure of each stage of the unit; 2) Calculate the spring stiffness and the piston diameter of the actuator; 3) Structural design of the unloading spring.

[0008] In step 1), the intake pressure at each stage is obtained: p s ={p s1 ,p s2 ,p s3 ,...,p sn} in: p s : indicates the intake pressure at each stage, and n indicates the stage number.

[0009] In step 2), the formulas for calculating the stiffness of each spring are as follows: in: Δ1: Represents the force difference at the lower stop point during the downward movement of the unloader; p h : Indicates the driving oil pressure of the hydraulic system during the downward movement of the unloader; d n : Indicates the piston diameter; k n : Indicates the spring stiffness of different levels of unloaders; x2: represents the amount of compression of the spring at the bottom dead center; Δ2: Represents the force difference at the top dead center during the upward movement of the unloader; p′ h : Indicates the driving oil pressure of the hydraulic system during the upward movement of the unloader; x1: Represents the amount of compression of the spring at the top dead center.

[0010] The hydraulic system maintains a constant driving oil pressure during the downward or upward movement of the unloader, and this pressure is consistent at all stages.

[0011] The equations for solving the unloader spring stiffness, piston diameter, and pre-compression amount belong to an underdetermined set of equations, which require comprehensive consideration of the effects of compression amount, piston diameter, and other factors.

[0012] To ensure that the unloader can move to the upper and lower dead centers and remain stationary, the force difference between the upper and lower dead centers must be satisfied. Considering friction and spring machining errors, the force difference between the upper and lower dead centers must meet the following conditions: |Δ1,Δ2|≥0.2max{p sn d n} To reduce the difficulty of piston machining in the actuator, the calculated piston diameter is retained to one decimal place. To increase the interchangeability of the actuator, the piston diameter of one stage is adopted when the piston diameter of each stage meets the following conditions: When |d i -d j When |≤1mm, d i =d j =min{d i ,d j} When piston diameters are similar, the diameter of one or more stages of pistons needs to be changed. The changed piston diameter needs to be substituted into the calculation formula for recalculation to obtain the final spring stiffness and actuator piston diameter.

[0013] The calculation of spring stiffness needs to take into account the safety of the system. The smaller the spring stiffness, the smaller the required hydraulic pressure and the higher the safety. Therefore, the minimum value that satisfies the calculation formula needs to be taken.

[0014] Step 3), structural design of the unloader spring: (1) Determining the spring diameter: in: D z : Indicates the mean diameter of the unloader spring; d: indicates the diameter of the unloader spring section; G: represents the shear modulus of the unloader spring material; n: indicates the effective number of coils of the unloader spring.

[0015] Because the spring diameter is limited by the radial installation space, the following conditions must be met: D z +d≤D1 D2≤D z -d in: D z : Indicates the mean diameter of the unloader spring; d: indicates the diameter of the unloader spring section; D1: Indicates the inner diameter of the unloader's outer casing; D2: Indicates the diagonal diameter of the unloader locking nut.

[0016] (2) Determine the free height of the spring: H = H1 + x1 in: H1: Indicates the height difference between the upper and lower contact surfaces of the spring within the spring mounting space of the unloader.

[0017] In summary, this application includes at least one of the following beneficial technical effects: 1. By accurately obtaining the intake pressure at each stage, combined with the force difference between the upper and lower dead centers of the unloader and the driving oil pressure of the hydraulic system, the stiffness of each spring and the piston diameter are calculated. This design method avoids the problem of inconsistent action performance caused by parameter mismatch, ensuring the synchronization of each actuator under uniform oil pressure; 2. By optimizing the design of the spring diameter and free height, the radial installation space is fully utilized, avoiding structural interference problems caused by insufficient installation space. Simultaneously, by controlling the deviation range of the piston diameter, the machining difficulty is reduced, and the interchangeability of parts is improved. 3. By comprehensively considering the relationship between spring stiffness, piston diameter, and pre-compression, the system safety issues caused by excessively high or low spring stiffness were resolved. By selecting the minimum spring stiffness value, the load requirements of the hydraulic system were reduced, further enhancing the system's operational stability.

[0018] In summary, this invention, based on the complexities of multi-stage reciprocating compressors, proposes a design method for the unloader spring and actuator piston diameter of multi-stage reciprocating compressors. This method ensures good consistency and synchronization of the actions of each stage of the actuator, and maintains consistent design margins for each stage. This improves the reliability, stability, and safety of the stepless gas volume regulation system of the reciprocating compressor. Attached Figure Description

[0019] Figure 1 This is a flowchart of the design of this invention; Figure 2 It is a graph showing the relationship between piston diameter, spring stiffness, and spring precompression. Detailed Implementation

[0020] The following is in conjunction with the appendix Figure 1 - Appendix Figure 2 This application provides a more detailed description of a design method for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor.

[0021] Example 1: Taking a 3-stage reciprocating compressor as an example, the following steps are included: (1) Obtain the intake pressure (absolute pressure) at each stage: p s ={1.3MPa, 2.5MPa, 5MPa} (2) The force difference at the lower dead center during the downward movement of the unloader is taken as 100N, and the force difference at the upper dead center during the upward movement of the unloader is -100N. The driving oil pressure of the hydraulic system during the downward movement of the unloader is 8MPa, and the driving oil pressure of the hydraulic system during the upward movement of the unloader is 4MPa. The stroke of the unloader is 3mm. The calculation formulas for the stiffness of each stage spring, piston diameter, and pre-compression are as follows: Where, x 2n =x 1n +0.003; The relationship between piston diameter, spring stiffness, and spring precompression is obtained by solving the problem. Get as Figure 2 The relationship shown: (1) Since the spring stiffness must be positive, the pre-compression must be greater than 0.002m; (2) The relationship between the piston diameter and spring stiffness of each stage is consistent. To avoid excessive differences in piston diameter, the spring stiffness of each stage should not differ too much. Therefore, it is necessary to adjust the pre-compression of each stage. As shown in the figure, the larger the pre-compression, the smaller the difference. However, considering that a large pre-compression will make installation very difficult, the maximum pre-compression should not exceed 0.01m. The initial selection is a spring compression of 0.01m for the first stage unloader, 0.003m for the second stage unloader, and 0.002m for the third stage unloader. Therefore, the spring stiffness and piston diameter of each stage are: After rounding the plunger diameter, the spring stiffness, plunger diameter, and pre-compression of each stage of the unloader are as follows: It has been verified that The conditions are met.

[0022] (3) Structural design of the unloader spring: Based on the calculation results of step (2), and combined with the installation space of the unloader spring, as shown in Table 1: Table 1. Dimensions of Installation Space for Unloading Springs series Diagonal diameter of the unloader locking nut Unloader housing inner diameter Level 1 32.95mm 80mm Level 2 32.95mm 70mm Level 3 26.17mm 70mm The springs are made of 65Mn material with a shear modulus of 78400 MPa. Based on the selection of wire diameter and number of turns, the final spring parameters for each stage are shown in Table 2. Table 2 Unloading spring dimensions series Free height Valid number of laps Spring stiffness Spring mean diameter Cross-section diameter Level 1 32.95mm 70mm 138117 N / m 57mm 8.5mm Level 2 32.95mm 70mm 83672N / m 52mm 7mm Level 3 26.17mm 70mm 18470 N / m 51mm 5mm After verification, the following conditions are met: condition.

[0023] Example 2: A design method for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor is disclosed. In practical implementation, it is first necessary to obtain the intake pressure of each stage of the multi-stage reciprocating compressor, which is the fundamental parameter for designing the unloader spring and actuator piston diameter. According to... Figure 1 In module 1 of the process, the formula for obtaining the intake pressure at each stage is as follows: P i = f(N) where Pi represents the intake pressure of the i-th stage and N represents the number of stages in the compressor. The intake pressure value of each stage can be obtained through actual measurement or theoretical calculation, and it can be used as important input data for subsequent calculations.

[0024] Next, we proceed to step 2, which involves calculating the stiffness of each spring and the piston diameter of the actuator.

[0025] The relationship between the hydraulic system's drive oil pressure and the actions of each stage of the actuators, and the calculation formulas for the spring stiffness of each stage are as follows: In this formula, Fdown represents the lower dead center force difference during the downward movement of the unloader, Fup represents the upper dead center force difference during the upward movement of the unloader, Pdown and Pup represent the driving oil pressure of the hydraulic system during the downward and upward movements of the unloader, respectively, Ap represents the effective working area of ​​the piston, and Ki represents the stiffness of the i-th stage spring. The driving oil pressure of the hydraulic system remains consistent throughout the up-and-down movement of the unloader and is the same at each stage; therefore, consistent action of each stage of the actuator can be ensured by unifying the oil pressure.

[0026] To ensure the unloader can accurately move to and remain stationary at its top and bottom dead centers, the force difference between these centers must be satisfied. Considering friction and spring manufacturing errors, the force difference between the top and bottom dead centers must satisfy the following relationship: |F down -F up |≥ΔF min Where ΔFmin represents the minimum allowable force difference. This condition plays a crucial role in practical design, ensuring that the unloader will not jam or fail to reach its designated position during operation. Meanwhile, to reduce the machining difficulty of the actuator piston, the piston diameter calculation result is rounded to one decimal place. A specific piston diameter can be used when the piston diameter of each stage meets the following conditions: D i ≈D j ±ΔD Di and Dj represent the piston diameters of the Di-th and Dj-th stages, respectively, and ΔD represents the allowable diameter deviation range. When piston diameters are similar, it is necessary to adjust the piston diameters of one or more stages and recalculate using the formula to ultimately determine the spring stiffness of each stage and the piston diameter of the actuator.

[0027] After completing the above calculations, proceed to step 3, which involves the structural design of the unloader spring. A schematic diagram of the unloader spring structure is shown below, and the formula for determining the spring diameter is as follows: In this formula, Ds represents the mean diameter of the unloader spring (3), Ki represents the stiffness of the i-th stage spring, ne represents the effective number of coils of the unloader spring, G represents the shear modulus of the unloader spring material, and ds represents the cross-sectional diameter of the unloader spring. Since the spring diameter is limited by the radial installation space, the following conditions must be met: D s +d s ≤D h -D l Where Dh represents the inner diameter of the unloader housing, and Dl represents the diagonal diameter of the unloader locking nut. This constraint ensures that the spring can function properly within the limited installation space, avoiding design failures due to structural interference.

[0028] Furthermore, the formula for determining the free height of the spring is as follows: H f =H c +H s Where Hf represents the free height of the unloader spring (4), Hc represents the height difference between the upper and lower contact surfaces within the spring mounting space, and Hs represents the spring's pre-compression. The free height of the spring directly affects its initial compression in the installed state, thus affecting the unloader's operational performance. Therefore, the height limitations of the mounting space and the spring's pre-compression must be comprehensively considered during the design process to ensure the unloader can operate stably and reliably.

[0029] In practical applications, the design method of this invention is applicable to the stepless air volume regulation system of a multi-stage reciprocating compressor. For example, in a four-cylinder, four-stage reciprocating compressor at an industrial site, the method of this invention first obtains the intake pressures of each stage as 0.1 MPa, 0.3 MPa, 0.6 MPa, and 1.0 MPa. Subsequently, based on the condition that the hydraulic system has a uniform oil pressure of 10 MPa, the spring stiffnesses of each stage are calculated to be 20 N / mm, 30 N / mm, 40 N / mm, and 50 N / mm, respectively. Based on this, the piston diameters of each stage are further calculated to be 50 mm, 55 mm, 60 mm, and 65 mm, respectively. After optimization and adjustment, the piston diameters of the second and third stages are finally unified to 58 mm to reduce machining difficulty and improve component interchangeability.

[0030] After calculating the spring stiffness and piston diameter, the structural design of the unloader spring was carried out. Based on the spring material's shear modulus of 80 GPa, spring cross-sectional diameter of 5 mm, and effective coil count of 10, the spring's mean diameter was calculated to be 40 mm. Considering the installation space constraints, the inner diameter of the outer shell was 100 mm, and the diagonal diameter of the locking nut was 20 mm, verifying that the spring diameter met the installation requirements. Simultaneously, based on the height difference of the upper and lower contact surfaces in the installation space of 30 mm and the spring pre-compression of 10 mm, the spring's free height was calculated to be 40 mm.

[0031] Through the specific implementation steps described above, this invention achieves a scientifically sound design for the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor. Each stage of the actuator operates with good consistency under unified hydraulic pressure, avoiding performance issues caused by parameter mismatch. The spring structure design fully considers radial installation space limitations, preventing design failures due to structural interference. Simultaneously, by optimizing the piston diameter deviation range, processing difficulty is reduced and component interchangeability is improved. The selection of spring stiffness balances system safety and operational stability, ultimately enhancing the overall performance of the multi-stage reciprocating compressor. To better enable those skilled in the art to fully understand and implement this invention, the following supplementary explanation of the specific implementation principles is provided in conjunction with a specific application scenario.

[0032] In a four-cylinder, four-stage reciprocating compressor at an industrial site, the method of this invention was used to design the unloader spring and the piston diameter of the actuator. First, the intake pressure values ​​for each stage were obtained using pressure sensors: 0.1 MPa, 0.3 MPa, 0.6 MPa, and 1.0 MPa, respectively, and these were used as important input data for subsequent calculations. According to... Figure 1 In the process step module 1, these pressure values ​​will be used to solve for the stiffness of each spring and the piston diameter.

[0033] Upon entering step 2, the hydraulic system maintains a consistent driving oil pressure of 10 MPa. According to... Figure 2 The relationship shown in the hydraulic oil pressure drive module 2 is used with the formula Calculate the stiffness of each spring stage. Here, Fdown and Fup represent the force difference during the downward and upward movement of the unloader, respectively; Pdown and Pup are the hydraulic pressures; and Ap is the effective working area of ​​the piston. Through actual measurement and theoretical calculation, the spring stiffnesses for each stage are obtained as 20 N / mm, 30 N / mm, 40 N / mm, and 50 N / mm. Based on this, the piston diameters for each stage are further calculated, with initial results of 50 mm, 55 mm, 60 mm, and 65 mm.

[0034] Since the diameters of the second and third stage pistons are similar, their diameters are adjusted to 58mm to reduce machining difficulty and improve component interchangeability. The adjusted diameter needs to be recalculated using the formula to verify whether it meets the condition for the difference in force between the top and bottom dead centers. |F down -F up |≥ΔF min Verification showed that the adjusted parameters met the requirements, ensuring that the unloader could accurately move to the upper and lower dead points and remain stationary.

[0035] Then proceed to step 3, which involves the structural design of the unloading device spring. Using the formula... Calculate the spring's mean diameter. Given that the spring material has a shear modulus of 80 GPa, a cross-sectional diameter of 5 mm, and 10 effective coils, substituting these values ​​into the formula yields a spring mean diameter of 40 mm. Considering the installation space constraints, the inner diameter of the outer casing is 100 mm, and the diagonal diameter of the locking nut is 20 mm. Verification confirms that the spring diameter meets the radial installation space requirements. D s +d s ≤D h -D l At the same time, according to the formula H f =H c +H s Determine the spring's free height. Given a height difference of 30mm between the upper and lower contact surfaces in the mounting space and a spring pre-compression of 10mm, the calculated free height of the spring is 40mm. This design ensures the spring functions correctly within the limited mounting space, avoiding design failures due to structural interference.

[0036] In actual operation, the hydraulic system applies a uniform oil pressure to each stage of the actuators via the hydraulic oil pressure drive module 2. Changes in hydraulic oil pressure directly affect the motion performance of the pistons at each stage. Because the spring stiffness and piston diameter at each stage are scientifically matched, the consistency of the actuators' movements is significantly improved, avoiding performance issues caused by parameter mismatches. For example, after the piston diameters of the second and third stages are standardized to 58mm, their response times become more consistent, reducing motion deviations.

[0037] Furthermore, by optimizing the piston diameter deviation range, the machining difficulty was reduced and the interchangeability of parts was improved. For example, during the machining process, the standardized piston diameter reduced the number of parts with different specifications, thereby reducing production costs and management complexity. Meanwhile, the selection of spring stiffness balanced system safety and operational stability, with a minimum allowable force difference condition |F down -F up |≥ΔF min This ensures that the unloader will not jam or fail to reach its designated position during operation.

[0038] In summary, this invention, through implementation in a specific application scenario, achieves a scientifically sound design for the unloader springs and piston diameters of the actuators in a multi-stage reciprocating compressor. Each stage of the actuator operates with excellent consistency under unified hydraulic pressure, avoiding performance issues caused by parameter mismatches. The spring structure design fully considers radial installation space limitations, preventing design failures due to structural interference. Simultaneously, by optimizing the piston diameter deviation range, processing difficulty is reduced and component interchangeability is improved. The selection of spring stiffness balances system safety and operational stability, ultimately enhancing the overall performance of the multi-stage reciprocating compressor.

[0039] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor, characterized in that, The method includes the following steps: 1) Obtain the intake pressure of each stage of the unit; 2) Calculate the spring stiffness and the piston diameter of the actuator; 3) Structural design of the unloading spring.

2. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 1, characterized in that, In step 1), the intake pressure at each stage is obtained: p s ={p s1 ,p s2 ,p s3 ,...,p sn } in: p s : indicates the intake pressure at each stage, and n indicates the stage number.

3. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 1, characterized in that, In step 2), the formulas for calculating the stiffness of each spring are as follows: in: Δ1: Represents the force difference at the lower stop point during the downward movement of the unloader; p h : Indicates the driving oil pressure of the hydraulic system during the downward movement of the unloader; d n : Indicates the piston diameter; k n : Indicates the spring stiffness of different levels of unloaders; x 2n : Indicates the amount of compression of the spring at the bottom dead center; Δ2: Represents the force difference at the top dead center during the upward movement of the unloader; p′ h : Indicates the driving oil pressure of the hydraulic system during the upward movement of the unloader; x 1n : Indicates the compression of the spring at the top dead center, x 2n =x 1n +L.

4. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 3, characterized in that, The hydraulic system maintains a constant driving oil pressure during the downward or upward movement of the unloader, and this pressure is consistent at all stages.

5. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 3, characterized in that, The equations for solving the unloader spring stiffness, piston diameter, and pre-compression amount belong to an underdetermined set of equations, which require comprehensive consideration of the effects of compression amount, piston diameter, and other factors.

6. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 3, characterized in that, To ensure that the unloader can move to the upper and lower dead centers and remain stationary, the force difference between the upper and lower dead centers must be satisfied. Considering friction and spring machining errors, the force difference between the upper and lower dead centers must meet the following conditions: |Δ1,Δ2|≥0.2max{p sn d n } 7. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 5, characterized in that, To reduce the difficulty of piston machining in the actuator, the calculated piston diameter is retained to one decimal place. To increase the interchangeability of the actuator, the piston diameter of one stage is adopted when the piston diameter of each stage meets the following conditions: When |d i -d j When |≤1mm, d i =d j =min{d i ,d j } 8. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 7, characterized in that, When piston diameters are similar, the diameter of one or more stages of pistons needs to be changed. The changed piston diameter needs to be substituted into the calculation formula for recalculation to obtain the final spring stiffness and actuator piston diameter.

9. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 3, characterized in that, The calculation of spring stiffness needs to take into account the safety of the system. The smaller the spring stiffness, the smaller the required hydraulic pressure and the higher the safety. Therefore, the minimum value that satisfies the calculation formula needs to be taken.

10. The method for designing the unloader spring and actuator piston diameter of a multi-stage reciprocating compressor according to claim 1, characterized in that, Step 3), structural design of the unloader spring: (1) Determining the spring diameter: in: D z : Indicates the mean diameter of the unloader spring; d: indicates the diameter of the unloader spring section; G: represents the shear modulus of the unloader spring material; n: indicates the effective number of coils of the unloader spring; Because the spring diameter is limited by the radial installation space, the following conditions must be met: D z +d≤D1 D2≤D z -d in: D z : Indicates the mean diameter of the unloader spring; d: indicates the diameter of the unloader spring section; D1: Indicates the inner diameter of the unloader's outer casing; D2: Indicates the diagonal diameter of the unloader locking nut; (2) Determine the free height of the spring: H = H1 + x1 in: H1: Indicates the height difference between the upper and lower contact surfaces of the spring within the spring mounting space of the unloader.

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