Gene Vogel
Pump & Vibration Specialist
Electrical Apparatus Service Association
St. Louis, MO
In his presentation at the EASA Convention 2011, Gene Vogel delves into the complexities of mechanical pump seals, categorizing them into pusher vs. non-pusher, cartridge vs. component, single vs. double (or triple), and balanced vs. unbalanced seals. Vogel emphasizes the importance of understanding these categories to ensure proper seal selection and installation, which is crucial for pump reliability and performance.
Pusher seals use a spring or tensioning device to apply pressure between the rotating and stationary rings, requiring the rotating ring to slide on the shaft. This can lead to leakage if the shaft becomes rough or corroded. Non-pusher seals avoid this issue by using a bellows or diaphragm, allowing the rotating ring to move independently of the secondary seal.
Component seals require careful assembly and adjustment, which can lead to poor performance if not done correctly. Cartridge seals, on the other hand, come as complete assemblies mounted on a shaft sleeve, simplifying installation and reducing the risk of improper assembly.
Balanced seals are designed to mitigate the effects of changing seal chamber pressure on face pressure, using an axial face machined on the opposite side to balance hydraulic pressure. Unbalanced seals do not have this feature and can suffer from excessive face pressure under varying chamber pressures.
Single seals have pumpage on one side and the atmosphere on the other, while double seals create a chamber between two sets of seal faces, often filled with barrier fluid to protect against abrasive or caustic pumpage.
Vogel discusses various seal face materials, including carbon on ceramic, silicon carbide, tungsten carbide, stainless steel, and Ni-resist iron. Each material has its advantages and limitations in terms of hardness, thermal conductivity, corrosion resistance, and cost. Seal faces must be lapped to achieve the necessary smoothness and flatness, measured using monochromatic light instruments.
Seal dynamics involve managing heat transfer, tensioning, and pressure velocity (PV) values. Excessive heat is a common cause of seal failure, and cooling flow through the seal chamber is essential to remove heat generated by friction. The pressure holding the seal faces together is a combination of mechanical tension and hydraulic tension from the seal chamber pressure.
Secondary seals such as O-rings must be compatible with the fluid being pumped and the operating temperature. Proper groove dimensions are crucial for effective sealing.
Seal flush plans ensure that liquid circulates through the seal chamber to carry away heat. Flush lines can be connected to either the suction or discharge side, with metering devices to control flow. Cyclonic separators can be used to remove abrasive debris from the flush fluid.
Vogel highlights the importance of accurately analyzing seal failure sources and applying engineering resources to design effective seals. Common failures involve controlling heat, managing abrasive materials, and ensuring chemical compatibility.
Key Points Covered:
- Categories of mechanical seals: pusher vs. non-pusher, cartridge vs. component, single vs. double, balanced vs. unbalanced
- Seal face materials and their properties
- Importance of lapping seal faces for smoothness and flatness
- Managing heat transfer and tensioning in seal dynamics
- Secondary seals and their compatibility with pumpage
- Seal flush plans and cyclonic separators
- Analyzing seal failure sources and applying engineering resources
Key Takeaways:
- Proper seal selection and installation are crucial for pump reliability
- Different seal categories address specific operational challenges
- Seal face materials must be chosen based on application requirements
- Effective cooling and tensioning are essential to prevent seal failure
- Secondary seals must be compatible with the fluid and temperature
- Accurate analysis of seal failures is necessary for designing effective seals
- Engineering resources can assist in optimizing seal performance and reliability
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