OT--Engineering Question

Jiles · Dec 27, 2014

I have worked in large industry with many different type pumps.
One of the simplest pumps I have ever worked on, is chainsaw oiler pumps.
Most are a tube with a close tolerance solid shaft inside that has a shallow flat machined across the outside diameter on the end and is rotated by a gear. Inline with the flat, on either side of tube, is a feed fitting and a discharge fitting.
I have never understood how, when the shaft is rotated, they can pump oil from the oil tank to the chain and bar, with no check valves of any type involved.

NCWayne · Dec 28, 2014

It's really no different than most other types of pumps. Basically the tolerance between the inner shaft and the tube it rotates in acts as a check valve, much like the tolerance between the gears and the sides of the housing do in a gear pump. From there, when the flat on the shaft passes the inlet port, head pressure from the oil tank forces oil into the cavity formed by the flat. As the shaft rotates the oil is carried around to the outlet port. In a pump like this the oil being moved isn't really being pressurized so much as is simply being conveyed from the tank to the outside. In any case, given the way liquids flow, when it reaches the outlet port, it is going to have a tendency to flow from it's container to the point of lowest resistance, which will be out the oiler tube and to the bar.

It's really a very simple setup when you get right down to it, but it works, and that's all that matters.

Russ from MN · Dec 28, 2014

I wonder of that's what my newest Jonsered has, if you leave it sit for very long with very much oil in the tank it leaks. The dealer checked it over when it was new and kind of said that's the way they are. It seems to be a bigger problem in the pole shed at the farm than if I have it home in my shop, a lot less temperature change in the shop.

Jiles · Dec 28, 2014

(quoted from post at 19:40:17 12/28/14) I wonder of that's what my newest Jonsered has, if you leave it sit for very long with very much oil in the tank it leaks. The dealer checked it over when it was new and kind of said that's the way they are. It seems to be a bigger problem in the pole shed at the farm than if I have it home in my shop, a lot less temperature change in the shop.

I think it's the same type pump. Not much of a way the oil can drain through the pump. In nearly every case I have dealt with, the leak comes from where the pipe enters oil tank or goes through case to supply oil to chain and bar.
I would suggest to give the saw a good cleaning and leave bar off with full tank of oil and try to determine where leak is.

MarkB_MI · Dec 28, 2014

I think those are essentially centrifugal pumps. Note there is almost zero pressure differential between the intake and discharge ports, so it doesn't need to generate much pressure. Nor does it have to deliver a lot of volume.

OT--Engineering Question

Jiles

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NCWayne

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Russ from MN

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Jiles

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MarkB_MI

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