edwardw
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Hey All,
After this weekends static testing we found one thing we needed to change about our data aquisition. Our current thrust measuring device was a 4 ton Harbor Freight hydraulic jack that was modified. We found one problem - the area of the cylinder was greater than 1 in^2. Why is this a problem? The reason is Pressure = Force/Area. When I press down with 10 lbs on the stand, the pressure was less than 10 PSI. That means that for every pound we didn't generate 1 PSI for our pressure transducer to pick up. Our resolution wasn't that great
While this was okay for our trial run, I decided something needed to be done.
What I came up with was a system that had an area of less than 1 in^2, and I only had to machine one piece. I decided to use a 6" long, 3/4" brass nipple. This has an inside diameter of .817" This would mean that my approximate area would be .52 in^2. This mean for each 1 LB placed on the stand - I would generate almost 2 PSI for the pressure transducer to pick up. This is much better. I also needed a way to measure the pressure - and dissapate the force of the motor into something. The solution there was a 3/4 brass tee - the kind that is machined from a solid piece of brass. This is flat on one side, making it perfect for sitting upright and standing by itself on level ground. And, since it was a tee - I could plug one side and use the other to hook up to my pressure transducer - two birds with one stone. The whole assembly is filled with nice thick automotive grease.
The only piece I had to machine was the 'piston', the part that would be putting the force on the fluid. It wasn't too hard - I bought some 1" solid stock. Then I turned it down to 10 thousands less than the inside of the pipe - to .807". I then put two grooves for o-rings at the bottom and then one near the top so that there would be no 'slop' when pressing down. I also left a shoulder at the top so that if a pipe burst - the piston would stop on the brass pipe and not go all the way down.
Below is a picture of the device, unassembled. There are 8 parts (not shown is the flare nut on the left side), and three o-rings. I think that it is pretty simple and straight forward. Some preliminary testing is yielding good results. I'm happy!
The total cost of everything was $25. I have a pressure transducer - so that isn't included. I didn't think that is too bad for this. Also, the reason we went with a pressure transducer instead of load cell is that when you cato - there is a big spike - most of the time this breaks the load cell. With a pressure transducer there is a fluid to absorb some of the explosion.
I was thinking of making these for other EX people on the forum - I would buy the brass pipe - machine the piston to fit - and send that too you. That way you could buy all the rest of the parts to fit your load cell. Good idea?
Edward
After this weekends static testing we found one thing we needed to change about our data aquisition. Our current thrust measuring device was a 4 ton Harbor Freight hydraulic jack that was modified. We found one problem - the area of the cylinder was greater than 1 in^2. Why is this a problem? The reason is Pressure = Force/Area. When I press down with 10 lbs on the stand, the pressure was less than 10 PSI. That means that for every pound we didn't generate 1 PSI for our pressure transducer to pick up. Our resolution wasn't that great
While this was okay for our trial run, I decided something needed to be done.What I came up with was a system that had an area of less than 1 in^2, and I only had to machine one piece. I decided to use a 6" long, 3/4" brass nipple. This has an inside diameter of .817" This would mean that my approximate area would be .52 in^2. This mean for each 1 LB placed on the stand - I would generate almost 2 PSI for the pressure transducer to pick up. This is much better. I also needed a way to measure the pressure - and dissapate the force of the motor into something. The solution there was a 3/4 brass tee - the kind that is machined from a solid piece of brass. This is flat on one side, making it perfect for sitting upright and standing by itself on level ground. And, since it was a tee - I could plug one side and use the other to hook up to my pressure transducer - two birds with one stone. The whole assembly is filled with nice thick automotive grease.
The only piece I had to machine was the 'piston', the part that would be putting the force on the fluid. It wasn't too hard - I bought some 1" solid stock. Then I turned it down to 10 thousands less than the inside of the pipe - to .807". I then put two grooves for o-rings at the bottom and then one near the top so that there would be no 'slop' when pressing down. I also left a shoulder at the top so that if a pipe burst - the piston would stop on the brass pipe and not go all the way down.
Below is a picture of the device, unassembled. There are 8 parts (not shown is the flare nut on the left side), and three o-rings. I think that it is pretty simple and straight forward. Some preliminary testing is yielding good results. I'm happy!
The total cost of everything was $25. I have a pressure transducer - so that isn't included. I didn't think that is too bad for this. Also, the reason we went with a pressure transducer instead of load cell is that when you cato - there is a big spike - most of the time this breaks the load cell. With a pressure transducer there is a fluid to absorb some of the explosion.
I was thinking of making these for other EX people on the forum - I would buy the brass pipe - machine the piston to fit - and send that too you. That way you could buy all the rest of the parts to fit your load cell. Good idea?
Edward
