How does a solenoid valve operate and what factors affect its behavior?

[CopyOfA]

Briefly, a solenoid valve utilizes a solenoid to move a soft iron core in such a way as to open/close an orifice to allow/inhibit flow of a fluid. I am a bit rusty on my E&M and I have a couple questions about this operation.

1) When a magnetic field is created using the solenoid, the soft iron core becomes magnetized, producing a north and south pole on the core, and essentially becoming a bar magnet. How does this core behave in the presence of the magnetic field? Since the solenoid will, in general, be short, the magnetic field is non-uniform inside the solenoid, so does that mean the magnetic field causes the core to move? Doesn't this violate the law that magnetic fields can do no work? If the magnetic field does not cause the core to move, why does the core move?

2) I looked around a bit, but I have not seen any literature showing an analytical model for the behavior of the valve as the coil (insulation and wire) degrades. I've seen equivalent circuit models, but not a more specific model. If anyone has leads on something of this nature, I would greatly appreciate it.


Thanks in advance for your help.

 

[anorlunda]

oesn't this violate the law that magnetic fields can do no work?

No. If that was true, there could not be electric motors. You are confusing conservative forces with no work.