Generic question

[Tofflemire]

Hello All,

I have this plastic cylinder that is 6" long and 1" dia with .1" wall. I have a stepper motor to move the plunger a controlled distance at 3 PSI. My problem is that when the plunger pushes the fluid a set distance (from start end) through a check valve, and if I move the plunger the same distance starting in the middle, I get less fluid out. What would be causing this difference in fluid output?

Tofflemire

 

[kcj]

Clarify please: Are you using the stepper motor to drive a ball screw that moves the piston? Essentially a syringe?

Is the fluid or check containing dissolved air? Does the output pressure change with syringe stroke?

 

[Tofflemire]

Hello,

Yes it is acts like a syringe.
All the air is removed.
As far I know the output pressure should not change. I am moving the piston the same speed and distance, just from different starting locations.

Tofflemire

 

[byrdj]

Could the plunger be deflecting, say when retracted to fill, the cup dishes out. the first push will dish it back in, giving the extra volume. If direction is not reversed, for all other pushes, the plunger will be dished in, giving the same volume.

 

[byrdj]

Also, is the distance being determined by electronics?. Is it possible there is non linearity in the measurement of distance at the end?

 

[Tofflemire]

Thanks, I will look into that, it maybe the problem.

Tofflemire