Normally closed magnetic valve A magnetic valve is built as

Normally closed magnetic valve. A magnetic valve is built as shown in Figure 10.55. The poppet is suspended on a series of thin arms that provide it with a spring constant k that keeps the valve closed. The spiral coil is fed with a current I that generates a magnetic flux density that is approximately linear, given as B = (a - r)CI [T], where r is the radial distance from the axis, a is the outer radius of the coil, and C is a measured constant (given) that depends on the number of toms, their density, and the ferromagnetic material\'s permeability. Estimate the current needed to completely open the valve, that is, to move the poppet up a distance d. Neglect gravitational forces and assume that the magnetic flux density in the gap remains unchanged as the poppet moves up because the motion is so small.

Solution

A solenoid valve is an electronically operated device. It is used to control the flow of liquids or gases in a positive, fully-closed or fully-open mode. The valve is commonly used to replace a manual valve or where remote control is desirable. A solenoid is operated by opening and closing an orifice in a valve body that permits or prevents flow through the valve. The orifice is opened or closed through the use of a plunger that is raised or lowered within a sleeve tube by energizing the coil. The bottom of the plunger contains a compatible sealing material, which closes off the orifice in the body, stopping flow through the valve.

The solenoid assembly consists of a coil, plunger, and sleeve assembly. In a normally closed valve, a plunger return spring holds the plunger against the orifice, preventing flow through the valve. When the coil is energized, a magnetic field is produced, raising the plunger and allowing flow through the valve. In a normally open valve, when the coil is energized, the plunger seals off the orifice, stopping flow through the valve.