Thermally Activated Piston Rod Seal for Standstill Leakage Control
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Solution Overview
Problem
Existing sealing devices for reciprocating compressors fail to provide a sufficient sealing barrier at standstill, leading to gas leakage due to thermal expansion differences between segmented packing rings and the piston rod.
Innovation Solution
A sealing device featuring a second packing ring made from a polymer material with a thermal expansion coefficient at least two times higher than iron, allowing for automatic thermally dependent activation and deactivation, and minimizing wear by reducing contact pressure during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an unsegmented sealing ring is used to prevent gaps at standstill, then sealing is improved, but the ring is constantly in contact with the piston rod leading to fast wear
Solution Approach 1:
The patent uses polymer material with high thermal expansion coefficient to change the dimensional parameters of the ring based on temperature. At operating temperature, the ring expands to create clearance, reducing contact pressure to zero or near-zero values, which dramatically reduces wear and extends service life. At standstill, it contracts to provide reliable sealing.
Solution Approach 2:
The invention makes the sealing ring dynamic by allowing its dimensions to change with temperature. The ring transitions from a contracted sealed state at standstill to an expanded non-contact state during operation. This dynamic behavior automatically adapts the ring's contact with the piston rod based on operational conditions, preventing constant wear while maintaining sealing when needed.
2Reliability
If a valve-controlled vent line is used to activate the sealing ring, then sealing during operation can be maintained, but the system becomes complex and requires external energy sources and control mechanisms
Solution Approach 1:
The patent enables the sealing ring to activate itself through thermal expansion. The polymer material's inherent thermal response to temperature changes automatically pushes the ring away from the piston rod during operation, eliminating the need for external valves, control systems, or energy sources. The system self-regulates based on temperature, greatly simplifying the overall device complexity.
Solution Approach 2:
The invention replaces the mechanical valve-controlled activation system with a thermal-mechanical system. Instead of using pressure differential controlled by valves to activate the ring, the patent uses thermal expansion of the polymer material to automatically generate the necessary radial force. This substitution eliminates complex mechanical control components and their associated energy requirements.
3Reliability
If polymer material with high thermal expansion coefficient is used for the packing ring, then automatic thermal activation and wear reduction are achieved, but the material selection becomes more restricted
Solution Approach 1:
The patent specifies a parameter range for the thermal expansion coefficient (at least two times higher than iron) rather than a single material. This parameter-based specification provides flexibility in material selection, allowing various polymer materials to be used as long as they meet the thermal expansion requirement. This approach balances the need for specific thermal properties with manufacturing flexibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures a tight seal at standstill and provides a leakage path during operation, maintaining effective sealing without external energy sources and accommodating various compressor applications, including those with suction pressures below ambient.
Implementation Method 1
the second packing ring is made from a material comprising a polymer, the material having a thermal expansion coefficient, which is at least two times higher than the thermal expansion coefficient of iron, wherein at or below a defined activation temperature an inner diameter of the second packing ring is smaller than an outer diameter of the piston rod to be sealed
Data Source
AI summary
In order to provide a sealing device (15) for sealing a piston rod (8) of a reciprocating compressor (1), which provides good sealing properties at compressor standstill, which has a simple structure, which allows for a simple handling and which requires no external source of energy, the sealing device (15) comprises a number of first packing retainers (18), each retainer including a retaining opening (18a) in which a first packing ring (19) is arranged, a second packing retainer (20), including a retaining opening (20a) in which a second packing ring (21) is arranged, the second retainer (20) being positioned closer to the second axial device end (15b) than the number of first packing retainers (18) in an axial direction of the sealing device (15), wherein the second packing ring (21) is an uncut ring, comprising a continuous inner circumferential sealing surface (21a), wherein the second packing ring (21) is made from a material comprising a polymer, the material having a thermal expansion coefficient (α), which is at least two times higher than the thermal expansion coefficient (αFE) of iron, wherein at or below a defined activation temperature an inner diameter (d_i) of the second packing ring (21) is smaller than an outer diameter (D_a) of the piston rod (8) to be sealed, such that in the mounted state of the sealing device (15) in the compressor (1) the second packing ring (21) is prestressed in a radial direction in order to form a tight seal between the continuous inner circumferential sealing surface (21a) of the second packing ring (21) and the outer circumferential surface (8a) of the piston rod (8), wherein at a given operating temperature, the inner diameter (d_i) of the second packing ring (21) is larger than the outer diameter (D_a) of the piston rod (8), such that in the mounted state of the sealing device (15) in the compressor (1) the continuous inner circumferential sealing surface (21a) of the second sealing ring (21) is detached from the outer circumferential surface (8a) of the piston rod (8) in order to provide a leakage path past the second packing ring (21) in the axial direction.