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Pump Characteristics Required in a Grease System

Generally speaking, lubricating greases in their semi-finished and finished states must be moved by positive displacement pumps, like Tri-Rotor rotary piston pumps, rather than centrifugal pumps.  As pumpage consistencies approach 3,000 SSU viscosity or greater, centrifugal pumps become impracticable, giving way to those of positive displacement design.  Besides requiring less power, these latter have low shear characteristics and so do not alter the consistency of grease by working it excessively.

If a grease is to be drawn from a tank or some such vessel, the pump must develop sufficient vacuum at its suction port to get the grease to flow out.  If the vessel is under vacuum, selection of the pump is particularly critical.

When grease consistency is so high or semi-solid to the extent that it will not flow quickly enough through the suction piping to satisfy the pump displacement, the pump will be starved.  The resultant cavitation may not only have a deleterious effect on the grease but will also ultimately damage the pump.  This means selecting a Tri-Rotor pump with sufficiently large suction port, and in some instances even with a top suction port.  Likewise, the size of the vessel discharge, the length and diameter of the suction piping, and the fittings in the suction line must be coordinated in proper relation with the pump.  Tri-Rotor will advise minimum size and maximum length of suction piping for their pumps in a given application.

Usually Tri-Rotor pumps in grease systems are furnished with integral bypass relief valves.  These valves protect the system in the event of a stoppage or an inadvertent closure of a valve in the discharge line.  It is preferable that the relief valve not be used as a metering or variable delivery device, because the shearing and wire drawing of the grease through the bypass valve assembly can adversely affect the uniformity of the finished grease consistency.  If the grease manufacturer wishes to vary the flow rates in a system, he can purchase Tri-Rotor pumps with variable speed drives or with variable volume control characteristics.

And if a grease is particularly shear sensitive, the Tri-Rotor pump design incorporates a low shear pumping principle.

Most pump suppliers to the grease industry make models which are also available with jackets so that temperature of the grease can be maintained at the desired level by circulation of steam or appropriate heat transfer media through such jacketing.

Usually standard petroleum-type packings are used in grease pump stuffing boxes instead of mechanical shaft seals.  This is particularly true for greases with solids inclusions such as bentonite, talc, and the like.

Since aeration of grease is undesirable, the pump handling it should be of a design which precludes entry of air, particularly one having good sealing characteristics along its shaft.

Positive Displacement Rotary Piston Pumps

Our industry makes available to grease manufacturers and users a broad spectrum of positive displacement pump designs.  There are many types:  gear, vane, progressive cavity, piston, and others.  Each design has its particular features and benefits but the rotary piston pump design is especially effective in grease applications.  Tri-Rotor has built up a large body of experience through thousands of successful pump system installations.  

The Tri-Rotor design utilizes two pistons within a rotor, instead of gears or vanes or lobes.  Double-acting, the pistons give four overlapping strokes per revolution.  The Tri-Rotor cycle reminds many engineers of a Wankel engine.  In their simple transfer or bypass configurations, Tri-Rotor pumps operate with fixed stroke lengths; discharge rate is directly proportional to RPM, and this performance is comparable to that of other positive displacement pump designs.

The Tri-Rotor pump line includes a third configuration, which is called the V-Head variable volume design.  Here the piston strokes are variable, either automatically or manually or remotely controllable.  The operator can control pump discharge rate infinitely from zero to 100% of the rating of the pump without stopping or changing its speed.  The V-Head principle provides great versatility in pumping, affording not only multi-flow rates, but also handling multi-viscosity pumpages ranging from the water like consistency of solvents and thinners to semi-solid substances such as grease and bubble gum.  Tri-Rotor V-Head pumps are widely used in proportioning and blending systems, metering, and in drumming and filling applications.

Please contact us if you have any questions about which is the best Tri-Rotor pump for your grease application.