Electromagnetic plunger pump

Claim 1

In an electromagnetic plunger pump, particularly using a half-wave rectified current as a power source, comprising an electromagnetic coil, a plunger case mounted along the center axis of the winding on said electromagnetic coil, an annular magnetic path and an annular magnetic pole located at opposite ends of the center axis of the winding on the electromagnetic coil and arranged in spaced juxtaposed relation so as to form a magnetic flux leaking portion therebetween, an electromagnetic plunger fitted in said plunger case for sliding reciprocatory movement along the center axis thereof having one end portion received in said annular magnetic path at all times during operation and shutdown of the pump, and a delivery plunger arranged coaxially with and adjacent to the electromagnetic plunger, said electromagnetic plunger and said delivery plunger being balanced and maintained in pressing engagement with each other in the vicinity of the magnetic flux leading portion by the biasing forces of an auxiliary spring and a restoring spring, the improvement wherein said electromagnetic plunger and said delivery plunger cooperating with the electromagnetic plunger are balanced and maintained in pressing engagement with each other by the biasing forces of the auxiliary spring and the restoring spring in such a manner that when the electromagnetic plunger is moved toward the annular magnetic pole to increase the sum of the deflections of the two springs so that the distance lb between the center of the winding or the magnetically neutral point of the electromagnetic coil and the magnetically neutral point of the electromagnetic plunger along the center axis thereof and the distance la between the end of the annular magnetic pole which is disposed anteriorly of the electromagnetic plunger with respect to the operating direction of the latter when the electromagnetic coil is energized and the end of the annular magnetic pole disposed in spaced juxtaposed relation to the electromagnetic plunger may have a relation 0.1<la/lb<1, the pump has a characteristic that its delivery pressure is reduced when the sum of the deflections of the two spring increases, whereby the delivery pressure of the pump can be stabilized in spite of a variation in the value of the pressure applied thereto.