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# Pipe inner diameter for greasing2

## Pipe inner diameter for greasing

(OP)
Is there any calculation to arrive at the optimum pipe inner diameter for having comfortable passage of grease through it.

Guess it will be a function of NLGI, length & pipe material.

This to extend greasing points away from the bearings for much comfort, but the pipe selection should also support the grease as well as it should pass properly.

### RE: Pipe inner diameter for greasing

2
i do not know whether there would be a standard method to determine the optimal diameter. i guess people found a diameter that worked and then used about the same diameter over and over again.

calculating it might also be rather difficult, since there are a lot of parameters that need to be taken into account. to name a few not already mentioned: lowest operating temperature, grease composition in terms of base fluid and thickener type, whether the piping is straight or has 90 degrees bends.

a good starting point would be to look at what manufacturers of lubricating equipment offer - most use flexible material with a relatively small diameter.

one thing to keep in mind: the NLGI number indicates the stiffness in a particular test - that unfortunately does not reflect the behavior of a grease in a longer line. in practice the type of thickener and the viscosity of the base fluid decide how much resistance to flow there is in a pipe, especially the type of thickener has a very large influence.

there exists a test to determine the resistance to flow of a grease in a pipe: the Lincoln ventmeter test. you can download a spreadsheet with results of that test here: Link

it clearly shows that various greases with the same NLGI number may behave quite differently.

### RE: Pipe inner diameter for greasing

Grease doesn't so much "flow" (like a fluid) as it squishes (like a toothpaste) - or, frankly, like "grease". It MUST be forced into the gaps and crevices between the two bearing surfaces or it has no lubrication effect.

So a very large tube becomes a pressurized storage vessel where there is very, very little flow rate of a viscous near-solid under high pressure. Larger the volume, longer the grease sits and degrades. Larger the volume, more chance of voids or low pressure zones when cold.

Longer the grease sits statically under high pressure, greater the chance it loses pressure if the tube or joint expands even a little. (Heat, vibration, flexing).

No internal pressure in the tube, or a lower pressure on a stiff or segregated or hardened mass the less will be forced out of the tube in between the bearing surfaces.

So, it's far better for the lubrication to have a small volume of grease being regularly "pumped" through the Zerc fitting in between the bearing surfaces. Unless you have some way of permanently keeping pressure on the entire grease mass.

### RE: Pipe inner diameter for greasing

Grease is also non-Newtonian, so that complicates any theoretical calculation of friction.

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(2B)+(2B)' ?

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