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Mechanical seals generate heat at the seal faces during operation. This heat can build up in the sealing environment, causing premature seal failure. Seal Support Systems help create optimal operating conditions by supplying cooling fluids (or gases) to the seal faces.
- Barrier Fluid Tanks / Reservoirs: Vessels for externally storing and delivering buffer or barrier fluids. Tanks are supplied with specific piping configurations as determined by pump, seal, and application criteria. Learn more about our ANSI Plus Seal Support System.
- Flex-A-Flo: A thermally actuated valve for removing hot barrier fluid. For use with dual seals. Learn more about our Flex-A-Flo Seal Accessory.
- Flowmeter: A device – available in single or double configuration — which regulates incoming flush water for cooling and lubrication. Learn more about our Flowmeter Seal Accessory.
- Heat Exchanger: A device used to cool process and/or barrier fluids within a supply line.
- PackRyt® bearing bushing: Works in conjunction with a mechanical seal to control and minimize the effects of radial runout while reducing the amount of flush media going into the sealed product. Learn more about the PackRyt® Seal Accessory.
Criteria such as process fluid, pressures and temperatures, the pump’s seal chamber pressure, and the operating parameters of the mechanical seal all influence the selection of a sealing support system. The American Petroleum Institute (API) Standard 682 contains over 30 specific piping plan diagrams and details to guide engineers and plant personnel in seal support selection. View the Flex-A-Seal Mechanical Seal Piping Plan Guide.
The API (American Petroleum Institute) Standard 682 classifies dual seals into two configurations. These configurations also apply to ASME (American Society of Engineers) B73.1 and ASME B73.2 pump designs.
Arrangement 2 (Unpressurized) Designs: the buffer fluid is the operating environment for the secondary seal and forms a “buffer” between the process fluid and the atmosphere.
Arrangement 3 (Pressurized) Designs: the barrier fluid is the operating environment for both the inboard and outboard seal, completely preventing process leakage to the atmosphere.
The API 682 Plan 52 is an unpressurized system consisting of a reservoir, supply and return lines, and an internal circulation device within the mechanical seal (commonly referred to as a pumping ring). The buffer fluid circulation rate is dependent on the support system setup (thermal siphoning) and how this circulation device functions during seal operation.
Reservoirs may be fitted with a variety of measurement devices such as a liquid level indicator and pressure gauges as well as valves, switches and transmitters to aid in various operation and maintenance functions. For instance, a typical support system configuration for natural gas liquids (NGL) would issue an alarm (visual, audible, or both) when the inner seal fails. In addition, the outer seal would take over the primary seal function until maintenance is performed.
The API 682 Plan 53A system forces gas from an external pressurized source into the reservoir to pressurize the barrier fluid. This means the reservoir pressure will be above seal chamber pressure; a guideline is a minimum of 20 to 25 psig (1.4 to 1.73 bar) above the maximum process pressure. The Plan 53A is also used to maintain a specific operating temperature range to ensure optimum lubrication at the seal faces. The reservoir houses a cooling coil which actively cools the barrier fluid as necessary.
As with the Plan 52, a circulation device is used to move the barrier fluid. Replenishing a Plan 53A system with fresh barrier fluid can be as simple as using a hand pump. Learn more about how API 682 Plans 52 & 53A Aid in Smooth Mechanical Seal Operation.
Buffer and barrier fluids may be either liquid or gas. These fluids lubricate seal faces during operation as well as regulate operating temperatures by removing heat—both generated and absorbed—away from the faces.
The top five qualities to look for in a buffer/barrier fluid include:
- Safe — environmentally and physically — for operators to use and store
- Not volatile or flammable; stable at ambient temperatures
- Good lubrication and flow values
- Compatible with the process fluid and the seal materials of construction—important to consider for start-up, operating, and upset conditions
- Inexpensive and readily available
General categories include:
- Water and glycol-based solutions
- Low viscosity hydraulic oils: petroleum-based or synthetic
- Heat transfer fluids
- Fuels such as diesel or kerosene, and alcohol solutions may also we used, but it is imperative that these fuels be evaluated for safety and compatibility before put into service.
We hope this article answers some of the most frequently asked questions about seal support systems. Please contact us if you have additional questions or would like more information about how Flex-A-Seal can solve your sealing challenges.