Understanding the facts and heeding these tips can help ensure the type of uptime your site needs from its compressor trains.
To date, this series has covered a number of available automated lubricant-delivery technologies. With the exception of Oil Mist, Air/Oil and Single Point Lubricating devices (all of which utilize a unique integral pumping unit), today’s centralized lube systems offer a variety of pump options to choose from. This article focuses on the differences in these options.
Once a delivery-system design is finalized, the next step is to select a suitable lubricant pump. This requires a review of the lubricated machine’s design and the customer’s cost constraints. To narrow the choices, the designer must answer several basic questions:
- Does the budget allow for the cost of a fully automated pumping system, or is the design restricted to a much less expensive manually actuated pump that can be upgraded or automated at a later date?
- Does the machine have an integral lubricant reservoir the pump can be mounted in or on, or does the pump require its own lubricant reservoir?
- Does the equipment have a mechanical power takeoff point, hydraulic or pneumatic power source available?
- Is an electrical power source available?
Mechanical-Powered Pump Units
If no electrical power source is available, the designer has no choice but to use a mechanically actuated pump. The pump design will usually employ a positive-displacement piston whose output delivery can be adjusted by restricting the length of the piston stroke. For most manually operated pumps, a lever arm is mechanically connected to a cam that moves a single acting piston pump back and forth (some designs use a spring-returned pump) with lubricant fed from an attached reservoir. The pump is actuated by manually moving the lever arm in a back-and-forth arc motion, drawing lubricant into the piston chamber that is, in turn, pumped into the distribution system through an internal check valve.
Fig. 1. A Series Progressive distribution system with a mechanical pump attached to a pitman arm arrangement at the end of a large-diameter rotating machine shaft (courtesy Engtech Industries, Inc.)
If reciprocating or rotary machine motion is available, the lever arm of the manual pump can be replaced with a power takeoff pitman arm linkage attached to the motion device. Figure 1 shows a series progressive distribution system with a mechanical pump attached to a pitman arm arrangement attached to the end of the large-diameter rotating machine shaft. The shaft attachment point is offset from the center to produce a reciprocating (up-and-down) motion of the arm that produces a rocking motion at the pump shaft, emulating the back-and-forth motion of the manual lever arm. By changing the length relationship of the pitman arm attachment point and arm length, the degree of arc will change and speed up, or slow down, the amount of pump strokes per hour. In this picture you can see that the pump setting is incorrect, evident by the excessive grease being pumped out of the bearing seal.
In smaller Single Line Resistance “oil-only” type systems, a spring return piston is employed. A single push of the lever pushes lubricant out through the meter valves to the lube points. As the lubricant is apportioned, line pressure dissipates and the spring return piston draws in the next lubricant charge.
Pumping lubricant to many points, over large distances, through large-diameter lines is typical of large Progressive and Dual-Line systems in heavy industries. These systems will typically employ a high-pressure pneumatic pump as seen in Fig. 2.
Fig. 2. A high-pressure pneumatic pump that’s typical of large Progressive and Dual-Line lube delivery systems in heavy industry (courtesy EngTech Industries, Inc.)
Pneumatic barrel pumps are unique in that they are designed to sit straight on top of a standard grease or oil drum, eliminating the need for a reservoir. The pump can deliver an output pump pressure of up to 70:1 airline input pressure. Pump design is again piston-style, and is usually controlled by a stroke counter or by line pressure depending on the distribution-system requirements.
(Note: In the early years of centralized-lubrication systems, the automotive industry, for one, utilized “on board” vacuum-operated lubricating oil pumps to automatically lubricate the suspension and steering components of luxury cars while they moved.) LMT
For more details on automated lube systems, as well as on ICML- or ISO-lubrication certification training, telephone (529) 469-9173; or email firstname.lastname@example.org.