in fig1 the difference is that when the engine speed is small even when the oil pressure of the oil pump is not large enough to operate i e open the valve unit 11 the indispensable minimum amount of lubricating oil can be fed to the lubricating oil pipe 15 through the passage 30 furthermore also when the piston 24 comes to the extreme right end position and when the oil pressure in the delivery pipe 5 is decreased so that the resistance valve unit 11 is closed the lubricating oil still continues to be fed to the pipe 15 by way of the bypass passage 30 it should be noted that since the diameter of the passage 30 is considerably small the lubricating oil passing through the passage 30 when the valve unit 11 is closed has almost no effect on the oil pressure acting on the cylinder 21 alternatively it is also possible to provide a bypass passage 30 39 in the needle valve 12 as shown by the broken line the passage 30 39 extends through the needle valve 12 between the pipe 5 and the annular groove 13 the role of the passage 30 39 is identical to that of passage 30 fig5 and 6 show an example of the directional.