Marshalsea Hydraulics . . . Oil lubrication v self lubrication

Pumps for water-based fluids Comparison of lubrication methods
Two distinctly different types of pump are commonly used for pumping water-based (water/glycol) control fluids. One type (self-lubricated) uses the process fluid itself as the lubricant for the pump's running components. The other type (oil-lubricated) uses a separate oil chamber to lubricate the pump running gear.		Pumps using the process fluid as a lubricant are essentially oil pumps being used as water pumps – self lubrication is the norm for oil pumps. The use of a separate chamber is specific to water pumps and was developed to allow water-based fluids with poor lubricating qualities to be satisfactorily pumped.

Advantages and disadvantages of the two types of pump
Self-lubricated		Oil-lubricated
Wear debris from the pumps operation contaminates the process fluid directly.		Wear debris is separated and does not enter the process fluid.

Catastrophic failure of the pump rotating group will introduce broken parts directly into the process fluid.		Debris from any internal failure is contained and does not enter the process fluid.

The process fluid is in direct contact with corrodable carbon steel components. This is contrary to most operators' policy of having the process fluid only in contact with stainless steel and other corrosion resistant materials.		The process fluid is not in contact with carbon steel components. All wetted parts are corrosion resistant.

Disconnection of the supply fluid will lead to rapid failure of the pump rotating group due to loss of lubrication fluid.		Separate on-board lubrication protects the pump if the supply fluid fails allowing indefinite running.

Pump type is not tolerant to prolonged dry running (ATEX identified predictable failure mode) temperature sensors and associated hardware are required for ATEX compliance.		Pump type is tolerant to dry running and does not require additional temperature sensors. Protection is provided by the on-board lubrication.

No periodic maintenance is required other than regular pump replacement.		Oil-lubricated pumps require a maintenance regime in line with other oil lubricated equipment (e.g., air compressors).

Single fluid provides both lubrication and process power.		Crossover exists between the process and the lubrication fluids. The use of polyglycol hydrophilic lubricants eliminates the mismatch normally found between mineral oils and water-based fluids with no adverse effects.

Self-lubricated pumps rely on the process fluid for lubrication. Choices made in fluid selection impact directly on the pump's performamnce and life.		Independent lubrication allows for a greater choice in process fluids and permits fluids with poor lubrication qualities to be selected.