Resulting Pressure From Thread Driven Hydrolic Piston

Hello BenJ and welcome to CR4. You will find lots of good people here who will try to help you out.

I have read through your request a few times now and am finding it difficult to visualise what you are trying to achieve.

Are you using the piston to "dispense" material and using the ball screw to drive the piston forward?

I am certain that in your enthusiasm you know precicely what it will look like, but I don't have great ESP powers.

There are some hints in your initial data that will help you. 2 oz in 25 seconds at 15 Bar will give you an energy requirement for your system (in a perfect world) and then you can factor in the losses (like friction in your gear set and the piston in it's travel) to understand the input power required of your stepping motor. (I'm sure you can do the calculations)

If possible, you might measure the piston position using a rotary encoder on the screw as this will give you better resolution.

Also, your material selection needs to considder the effect of any conducted heat through the piston walls and also the piston shaft. The conducted heat could affect the seals, but also items remotely attached to the shaft.

If you can do a small sketch and include it in a reply or else describe something that is similar that people might be familiar with would help.

well, i understand that i was a bit vague. but i am trying to reveal as little of the design as possible as it is my strong opinion that i have a great invention. so I'm try to give some other examples without saying what my design is. i really cant tell any details about what the machine is, but it would be nice, as it would greatly help. but until i get a patent this is the way i am keeping it.

so yea, as i said its a piston and cylinder, the piston will have a seal that is heat proof and does not leak at high pressures, the cylinder is made of brass and has a band heater around it to heat the water inside the cylinder as it is pulled in. good point about heat being transfered to the stepper through the piston! didn't think of that really.

yes, the piston is driven by the screw by the stepper, i also think that another important spec to bring up again is the fact that the piston/cylinder will have a 3" ID as you remember. and of course the larger the area in the cylinder, the less forward motion and the more force needed.

by the way I'm really just a home hobbyist that only has a GED, 20 years old, and just love to tinker with things and build things from parts from other things, anything i know about designing and engineering is self taught. just FYI... not to good at much math at all, but i excel in understanding mechanical theories and basic intuitive physics, i know its a bit of a brag. but think about Benjamin Franklin, he did great things without having much ed.

The force the ball screw must exert on the piston is almost 1600 lb. If you went to a 1.5" x 24" cylinder, the force would a bit less than 400 lb.

For whatever reason, 5/8" x 13/64" ball screws and nuts are quite economical in McMaster-Carr. It would turn about 25 rpm to give your linear speed. (Quickie calc needs review.)

The narrower but longer cylinder would give you twice as much heat exchange surface, if needed.

I haven't yet looked at torque requirements and what you can get from various stepper motors or gearmotors.

This looks like a good concept for a programmable precision liquid injection system.

do you mean 1600 lb of force for the forward stroke of the piston or of the foot lbs of rotary force? although i do see that you said you did not figure the torque, so you must mean linear force. wow thats a lot! i thought that the psi/bars in the cylinder would be the same as the force in lbs of force exerted on the piston. but now that i think about it a bit deeper, the psi in the cylinder is more a factor of the pressure across the entire area of the piston then a simple single dimensional linear force in the center. am i correct?

i don't know any of the math as i have not gone to collage, but the basics make a lot of sense to me.

so i will need a pretty hefty screw for this. good recommendations about changing the shape of the cylinder, but one of the other requirements is that this system be able to fit in a small space. and i may change the shape some after i build a prototype and face some trial and error situations.