OT. Need some clarification on a formula

[Clay B. 1]

I just recieved my guide to Fluid Power Motion Control from Delta Computers ( will take me days to gleam all the useful info here). My main reason for getting this book is beacuse of a question I posted in another thread. What I am looking at right now is the formula for calculating cylinder size. The formula in question A avg= (fX4)^2 X pie ^2 X Ls XWs / (g xB) A avg is the average area of the pistion f is the cycle frequency Ls is the stroke length Ws is the weight of the load g is acceleration due to gravity (32 ft/sec^2) B is the bulk modulus (incompressibility constant) of oil (aprox 200,000 psi) My question is this. If my cylinder is mouted to travel in horzonial plane and the weight is supported then do I assume that g is zero? The reason I ask is when I look at this formula it seems to me that every other factor increases the cyclinder size as they increase where as gxb reduces the size. If that is truly the case (and I am not really off my rocker as usual) then I would have to assume some friction due to my supports of the load having to be taken into acount and that this friction adds directly to the Ws(weight componet of this formula). We have injection molding machines where I work at now and all cylinders are moving in a horizonal direction. I want to use this formula and others I have recently aquired (thanks Peter) to get a better understanding of these systems.

[paulengr 44]

No. G is just a constant. It doesn't have to do with the position of the cylinder. Another example is calculating the pressure under water (density X G X height), or converting from mass to weight, often used for force calculations. As to B reducing the cylinder area...yes. As the incompressibility increases, the cylinder area can decrease. However most of the time, you can't change this.

[Keith Menges 0]

You can look at it one of two ways. In the English system, dividing weight by gravitational acceleration gives you mass in slugs, which is the customary english unit of mass. Or you can divide linear acceleration by gravitational acceleration to give you acceleration in G's. Ultimately you are trying to satisfy the equation: F = m*a and get the units to work out right. Keith

[Peter Nachtwey 15]

Since we measure how heavy every thing is in force we must divide by the force of gravity to get mass. If we use SI units we would be talking Kilograms which are units of mass. Not Newtons which are units of force. In other words the rest of the world does it right and we do it wrong. The cycle frequency is 1 over two times the time it takes to ramp up. The point is that if you want to accelerate or decelerate faster you need more piston area. Eventually this gets to be very expensive. Edited 18 Mar 2008 by Peter Nachtwey