Gene Vogel
EASA Pump & Vibration Specialist
Submersible pumps are a common machine repaired in EASA service centers. Almost all submersible pumps have dual seals, an upper (inner) seal and a lower (outer) seal. The chamber between those two seals is the seal chamber and it will be filled with some type of barrier fluid. The most common barrier fluid is oil; although, some models (Figure 1) are designed with a glycol solution barrier fluid. The proper barrier fluid for each model of pump will be listed in the pump operation & maintenance (O&M) manual, and EASA’s primary recommendation is to use the specified fluid. When the fluid specification cannot be found or when the specified fluid is not available for the repair, there are some general guidelines to follow that are offered here.
Figure 1: The seal chamber, between the inner and outer seals of a
submersible pump, is filled with barrier fluid.
There are many considerations for selecting a barrier fluid in general, but only a few apply to submersible pumps. For instance, submersibles seldom operate in high ambient temperatures, so those concerns are moot. The primary purpose of barrier fluid is to lubricate and cool the contacting seal surfaces, and those are the key factors for selecting a barrier fluid for submersible pumps. Two fluids that offer good lubricity and cooling are oil and glycol solution; those are the fluids pump manufacturers use in the vast majority of submersibles. Another concern is compatibility with the seal materials, especially the elastomer components. If repairers are not familiar with the compatibility requirements of elastomer materials, they should consult with seal vendors who can provide that information. And finally, another concern is compatibility with the pumpage and the environment in general. Seals sometimes fail and barrier fluid can leak into the pumpage. As an example, a submersible pump leaked seal oil into a city fountain. The necessary cleanup was quite expensive.
Figure 2: The viscosity of the seal oil depends on the operating temperature of the pump. ISO 32 is most common.
The barrier fluid most commonly specified by pump manufacturers is turbine oil, sometimes stated as paraffin oil (turbine oil is a paraffinic base product). The oil must have good lubricity yet be free flowing at the pump operating temperature. Since submersible pumps operate in a relatively cool ambient temperature (Figure 2), an International Standards Organization (ISO) 32 turbine oil is a good choice. There are some submersible pump applications where the pumpage is quite hot or quite cold, and in those applications, appropriate ISO viscosity oil should be selected. Oil vendors can provide detailed data on operating temperatures for their products.
If the application includes the potential for the barrier fluid to contaminate the pumpage, as in the public fountain example above, food processing applications or similar situations, repairers should investigate the proper National Sanitation Foundation International (NSF) classification. Once that classification is determined, vendors can recommend products with the proper rating and viscosity. Often, submersible pumps for these applications specify a glycol solution (ethylene glycol or propylene glycol) (Figure 3).
Figure 3: Similar to oil, the viscosity of glycol solution barrier fluid must be appropriate for the operating temperature.
It would seem that filling the oil chamber on a submersible pump would be a simple task. However, while it is not difficult, there are procedures specific to each pump model, and the consequences of not doing it correctly are severe. When the pump is in operation, the fluid level must flood the upper seal, providing it with lubrication and cooling. If the fluid level is too low and does not flood the upper seal, the seal will overheat in minutes and be ruined. It is also necessary for there to be an air pocket above the fluid level to accommodate thermal expansion of the fluid. If the chamber is overfilled and the air pocket is eliminated, excessive pressure will cause seals to blow out and fail. Some manufacturers install an inflated donut in the seal cavity. The filling procedures for the specific pump listed in the O&M manual must be followed.
Making sure a submersible pump has the proper barrier fluid filled to the correct level is one of the easier tasks for pump repair. But it is not a task that should be ignored. Consulting the O&M manual for the pump, adhering to the guidelines offered here and working with barrier fluid vendors will ensure the simplest part of the repair doesn’t result in a premature failure.
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