Abstract: An object of the present, invention is to suppress the decrease in seal performance by avoiding wide-area contact between a valve face and a valve seat face which contact results from the non-circularity of the valve face and the valve seat face.

Abstract: The problems can be solved by ensuring that Ga≦Gb<Gc or Ga<Gb≦Gc, wherein Ga denotes a clearing between the bore on the portion from the compression chamber of the high pressure pump to the cylindrical groove and the plunger, where a transverse aperture is connected with the bore through a cylindrical groove provided halfway through the bore of a cylinder; Gb a clearance closer to the cylindrical groove, out of the clearances between the bore from the cylindrical groove to the drive source side and the plunger; and Gc a clearance closer to the drive source side, out of the clearances between the bore from the cylindrical groove to the drive source side and the plunger.

Abstract: By grinding the grinding surface of a diamond grinding tool which is formed in a predetermined shape by securing diamond abrasive grains by bond circularly or flat with high accuracy by the processing type truing method, uniformly dressing the above bond surface so as to project diamond abrasive grains, lapping the tips of the diamond abrasive grains projected from the above bond by the lapping type truing method so as to make the cutting edge height constant, the run,out of the grinding surface can be controlled to the order of submicrons and the cutting edges which are tips of the diamond abrasive grains can be aligned precisely.

Abstract: This invention provides a lap capable of reducing the pole recession produced between the substrate and the magnetic film when the air-bearing surface of a thin-film magnetic head is lapped, a lapping liquor used for such lapping, and a thin-film magnetic head having its air-bearing surface lapped by using them. Lapping is carried out by using a lap made of a material having both a phase of tin and a phase of brass with a greater rigidity in supporting the abrasive grains than tin, and a lapping liquor prepared by mixing an anionic surfactant (15) and an ampholytic surfactant (16). According to the present invention, it is possible to reduce the pole recession in the thin-film magnetic heads and to accordingly shorten the recording bit length of the magnetic discs.