Liquids used for barrier or buffer fluids are essential in maintaining proper operation of equipment requiring mechanical moving parts, such as pumps. Measuring and ensuring proper liquid levels in seal pots, for example, can help protect expensive equipment.
At a minimum, low level indication is required to ensure there is liquid in the vessel or seal pot. However, industry standards are moving toward continuous measurement utilizing transmitters. Modern ultrasonic level switches and guided wave radar level transmitters offer advantages over differential-pressure transmitters in such applications.
For end-users, ultrasonic level switches and guided wave radar level transmitters offer accurate performance, advanced diagnostics, and no calibration necessary regardless of specific-gravity changes. For seal pot manufacturers, these instruments provide a variety of price and performance options, with worldwide safety approvals.
The influence of API 682
API Standard 682, Pumps—Shaft Sealing Systems for Centrifugal and Rotary Pumps specifies requirements and gives recommendations for sealing systems and seal accessories for centrifugal and rotary pumps used in the petroleum, natural gas, and chemical industries. It is applicable mainly for hazardous, flammable, and/or toxic services where a greater degree of reliability is required for the improvement of equipment availability and the reduction of both emissions to the atmosphere and lifecycle sealing costs.*
The third edition of the API Standard 682 was released in September 2004. Revision 3, which combined with ISO 21049, specifically mentioned the use of ultrasonic switches.
Ultrasonic level switches that employ high-frequency sound waves, can easily transmit across a transducer gap in the presence of liquid media, while also attenuating when the gap is dry. This capability is particularly well suited for seal pot applications.
API Standard 682 Revision 4 was released in May 2014. Revision 4 introduced the use of indicating transmitters, specifically hydrostatic, as well as other technologies that meet purchaser approval if specified. This includes the substitution of switches in place of transmitters. However, if transmitters are selected, the recommendation is that they should be analog, two-wire type instruments with 4-20 mA output.
Level solutions for lubrication fluid monitoring
Guided Wave Radar (GWR): Offers significant advantages over differential-pressure transmitters. GWR measures level directly, there’s never an error associated with density (SG) or other changes in the liquid, and no calibration is required.
Current Shift Ultrasonic Level Switch: Two-wire device povides discrete mA outputs with continuous indication (8 mA is normal operation, 16 mA is level alarm). Meets NAMUR NE43 recommendations (3.6 mA or 22 mA) for malfunction indication to provide 4–20 mA range. The most economical option for API Standard 682 Revision 4.
Top-Mounted Current Shift Ultrasonic Level Switch: Two-wire device with top-mounted option to eliminate the need for taps. Provides discrete mA outputs (8 mA is low level alarm, 12 mA is normal operating level, 16 mA is high level alarm). Meets NAMUR NE43 recommendations (3.6 mA or 22 mA) for malfunction indication to provide 4–20 mA range
Ultrasonic Single Point Relay Switch: An excellent solution for reliable single-point liquid level indication. No calibration or density configuration required. Suitable for Safety Integrity Level (SIL) 2 loops.
Ultrasonic Dual-Point Relay Switch: Utilizes two independent switches in a single instrument to achieve low-level and high-level indication. No calibration or density configuration required. Top-mounted to eliminate taps and reduce costs. Suitable for Safety Integrity Level (SIL) 2 loops
For more information on level measurement solutions for lubrication liquids in rotating equipment, download the liquid level solutions for seal pots brochure.
This content is sponsored by Magnetrol International. Sponsored content is authorized by the client and does not necessarily reflect the views of the Process Flow Network editorial team.
* "API Standard 682, Pumps—Shaft Sealing Systems for Centrifugal and Rotary
Pumps," American Petroleum Institute.