Electromagnetically operated valve unit

In an electromagnetically operated valve unit for controlling the quantity of fluid flow in proportion to an electric current applied thereto, said valve unit comprising:

• a casing of magnetic material having inlet and outlet ports;
• a support shaft of non-magnetic material fixed in position within said casing and having an axial bore in open communication with one of said inlet and outlet ports and an axial hole formed in the peripheral wall of said axial bore to provide fluid communication between said inlet and outlet ports;
• a plunger of magnetic material in the form of a sleeve member axially movable on said support shaft and cooperating with the axial hole of said support shaft to open and close the fluid communication;
• resilient means for biasing said plunger in one direction to normally close the axial hole of said support shaft;
• a tubular yoke assembly including a pair of tubular members of magnetic material and an annular member of non-magnetic material concentrically arranged with said support shaft and facing at their inner circumferences the outer circumference of said plunger with a predetermined annular clearance;
• and
• a solenoid coil wound around said tubular yoke assembly to be energized by the electric current;
• the improvement wherein said plunger includes a pair of large diameter portions and a small diameter portion between the large diameter portions, the axial length of each of the large diameter portions being substantially equal to the axial length of each of said tubular yoke members, and wherein the large diameter portions of said plunger face the inner circumference of said yoke assembly with said predetermined annular clearance and are formed respectively at their outer circumferences with a plurality of grooves in such a manner that the outer circumference area of each of the large diameter portions is substantially equal to the cross-sectional area of the small diameter portion.