Wow, this has got to be boring some of the readers here, but it's great stuff.
I'm still struggling with the idea that the ball version has more mechanical gain. I've not studied fluid flow in decades but I always try to visualize what is going on in any physics situation. Jarrid writes:
I can't picture that. When the ball is half way across the port, looking from the outside you would see the widest part of the ball centered in the hole and you would see the pressure side hemisphere still partly obstructing your view, similarly partially blocking flow. Another visual: With the ball half way across the port, look into the open end of the tube while having the area outside the tube well lit. Surely you would see less light entering the tube from the outside than you would with a flat piston halfway across the dump port. And when the wide part of the ball finally clears the full port there is still the hemisphere partially blocking the flow. Full flow will not be achieved until the last portion of the ball clears the port. The piston version only needs to move the diameter of the port to go from no flow to full flow. But the ball version needs to move the full port diameter plus half the ball diameter to go from zero to full. That seems to me to be a decreased mechanical gain. I'm sure the graphs of flow vs position is not a straight line for either design, but I can't visualize it being significantly steeper for the ball at any point.
Tom
First, before the physics talk, I need the diameter and location (and quantity) of the dump ports for the design with the bronze tube and the threads at the wrench end so I can redo my design. Thanks in advance to anyone who would be kind enough to do some measurements.
The ball does not have more mechanical advantage; the oil is only pushing the ball one way so the oil pressing against the ball 'towards the center' is negated and it's the same as a plunger of the same diameter. When I first read that comment I thought he was actually talking about the difference between square and round dump ports; now I'm not sure what he was talking about; there is nothing I can see that would be 4x anyway.
I think you are actually both arguing different ends of the same concept, one that certainly has effect but that I think has a very small effect. He is basically saying that if you spray a cube and a baseball with a fire hose the cube will bounce more water back at you, less off to the sides. You are saying that if the items are right at the end of the hose and the baseball is slightly inside the end of the hose then the baseball will cause more restriction, thus reducing the flow.
The issue with the first argument is that the pressure differences are great enough that the "water bouncing back at you" would be almost impossible to measure. It would be measurable in a closed system like we have, but we are still talking pretty small numbers compared to the opening pressure. The issue with the second argument is that the combined cross-sectional area of the ports is smaller than the ball; the maximum flow for the ports is achieved well before the maximum flow for the ball. Basically I'm saying that if you put something small right at the end of a fire hose the water pressure will just fling it out of your hand. I know this is oversimplified, but sometimes physics is easier if you think of things you could do in the real world.
It is useful to remember that pressurized oil is not light. Light bounces at angles and it gets absorbed. Oil is happy to creep up 2 inches of threads if they are not properly sealed. Oil also pushes (I know light does as well but it's hard to detect if you are not in outer space). Pressurized oil will go wherever it can and as long as the restriction isn't significant (like the threads example) then the flow will not be significantly effected.
I really don't think that the ball concept is problematic from a flow or frequency standard. The main issue I have is with the ball-spring interface. I don't really want a spring touching the ball or possibly rocking towards the release ports and jamming as it ages. I also don't want to have to get a mating piece made, or to buy the tooling to do it myself. Given proper materials I believe the wear would be the same between both designs, except that the piston would wear a longer section. The ball would also be better at skipping over ridges, but with enough chamfer the piston would do that well enough, at least up to the point that the tube was so worn that it needed to be replaced anyway.
So basically I'm back to the original piston design, except with a better spring I found. Once (if) I find out what the original dump ports were I'll fine-tune it and either make it or have it made...or if that website actually has NOS OPR's hidden somewhere maybe I'll just buy one of those and leave the final drawings here so that when they run out the next person can go to a machine shop with them.
