Maintenance Technology April 2017 - 45

LUBRICATION STRATEGIES

Specify the Right
Lube-Delivery Line

Ken Bannister
MEch Eng (UK)
CMRP, MLE
Contributing Editor

The wrong lubrication-delivery line can compromise the
reliability of your production equipment.
DURING LUBRICATIONTRAINING workshops, I ask participants to name the
components that make up a centralized lubrication system. Most will answer in the context
of an automated-delivery system by citing the pump, reservoir, metering devices, and pump
controller. Rarely do they actually include the lube-delivery lines in their answers.
Lubrication-delivery lines are important and integral components within centralized lubrication systems-be they state-of-the-art automated designs or simple, manual arrangements.
Specifying the wrong type can put machinery reliability at risk.
The function of a lubrication-delivery line is straightforward: It must connect a bearing
point to a lubricant source (indirectly from a meter or gang block, or directly from the pump)
and allow the lubricant to be contained within the line to flow without constriction. As
lube-delivery systems are hydraulic in nature, the line must also be capable of withstanding
pressures ranging from hundreds to, in some cases, many thousand of pounds-per-squareinch (psi) of pressure.

Line size and material
Correct choice of size and material is essential if a lubricant-delivery line is to provide reliable
Fig. 1. Cost should not be a factor
service. For the most part, the line plays a passive role within a centralized system and is
in your lubrication-delivery-line
typically fixed to the side of a machine (the exception being where a lubricated part moves
choices. While the steel-tubing in
independently of a piece of fixed machinery, in which case, the line is used to provide the
this progressive-divider-lubrication
flexible connection.) Before a delivery line can be specified, however, a number of basic
system block took more time to
questions regarding the overall lube-system design must be answered, including:
install than plastic lines, the addi1. Is this system automated or manual? The answer is crucial in assessing line matetional, but small, up-front cost will
rial, diameter, and wall thickness, which relate specifically to the line's material-burst
pay long-term dividends, especially
pressure rating.
if leaks or blockages occur.
S Manual systems designed to "gang" grease nipples in a central block can be
lubricated by grease guns capable of developing as much as 15,000 psi.
S Manual hand pumps and automated systems operate at much lower
pressures (between 100 and 2,000 psi).
Fig. 2.
The bundled plastic
2. What type of automated/engineered delivery system is specified? Some
tubing in this
system designs require a single line size throughout, whereas others
progressive-divider
require a main and secondary line of different diameters and flow rates.
system are difficult to
For example:
individually trace from
S Single-line-resistance and pump-to-point systems are low-pressure
pump to the lube
systems designed to deliver the total amount of lubricant in one pump
block. These types of
cycle. In such systems, i.e., total-loss, single-size-diameter delivery
lubrication-delivery
lines are sufficient.
lines are also difficult
S Single-line positive-displacement-injector, dual-line-injector, and
to physically attach
progressive-divider systems require multiple cycles of the pump
to a machine's frame
connected to a larger diameter main line used to rapidly fill the injecand, consequently,
tors/main distribution blocks, and smaller-diameter secondary lines
more vulnerable to
that connect the metering outlets to the lubrication points,
damage.
S Re-circulating-oil systems usually require single-size-diameter
delivery lines and a larger-diameter, return-line system.
APRIL 2017

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