Shopsmith Forums

I would think the air in the chamber would heat up under use and would need somewhere to go as it expands otherwise it would be forced out thru the seals.

fredsheldon wrote:I would think the air in the chamber would heat up under use and would need somewhere to go as it expands otherwise it would be forced out thru the seals.

I would think that there wouold be a vent hole in that chamber for this very purpose.

Seriously, I can feel the air moving out of that vent hole as if it's being pumped out. It's not a lot mind you, but its there.

Just got an idea, I'll have to find a balloon first. I'll hold the balloon opening up tight against the vent hole and see what positive and/or negative pressure effect have on the balloon.

Check back later!

dusty wrote:I would think that there wouold be a vent hole in that chamber for this very purpose.

Uh, there is a vent hole.

pieceseeker wrote:Uh, there is a vent hole.

Maybe there needs to be a balloon premanently attached over the vent hole. Sort of like a repirator. The balloon signifies the health of the pump.

The only things that would need to be added then, is bells and whistles!

Well this is certainly getting deeper into the 'situation'.

I overlooked the heat expansion of the air(as well as the oil).

Dusty, the lower chamber does have a bleeder hole - the cotter pin hole). I also forgot about that for the lower shaft. I was concentrating on the upper shaft which does not need relief. The volume inside the crankcase does not vary(upper shaft out, lower shaft in and vice-versa).

My initial reaction to the cotter pin was the same - why? My current very unsure recollection was I concluded it served as a stop while assembling.

The air/oil in the lower chamber is indeed undergoing volume changes as the shaft moves in/out. As previously stated that is relieved through the cotter pin hole. So de pump has been found!!! The crankcase pressure will indeed oscillate.

Maybe the cotter pin serves as a flow control for the lower chamber 'bleeder' hole.

My old online obtained manual does not include de cotter pin etc, but I remember it being in thar!

Well, my balloon test to demonstrate the pressure changes in the crankcase has failed miserably. Too much volume in the deflated balloon to show the minute changes in pressure.

So, I cut a 1" x 2" strip of cellofane to demonstrate. Taped it to the side of the jigsaw and over the vent hole. Here is what I saw.

The vid is not really clear, but the movement of air in and out the vent is obvious.

http://www.youtube.com/watch?v=W5u0cQ1EIMk

Apparently, a fine oil mist is also dispersed out this vent hole (residue on the cellofane), hence the accumulation of gummy gunk in the hole over time...especially with wood fibre floating in the air!

pieceseeker wrote:Well, my balloon test to demonstrate the pressure changes in the crankcase has failed miserably. Too much volume in the deflated balloon to show the minute changes in pressure.

So, I cut a 1" x 2" strip of cellofane to demonstrate. Taped it to the side of the jigsaw and over the vent hole. Here is what I saw.

The vid is not really clear, but the movement of air in and out the vent is obvious.

http://www.youtube.com/watch?v=fzB978HE-1c

Apparently, a fine oil mist is also dispersed out this vent hole (residue on the cellofane), hence the accumulation of gummy gunk in the hole over time...especially with wood fibre floating in the air!

This video is private.



Ed

oops! I'll try to fix.