| 摘要 |
<p>PURPOSE: To reduce pressure loss by enabling pressure control in a middle range without the necessity of an independent pressure regulating mechanism. CONSTITUTION: In this counter flow preventing device, a straight passage 9 formed in an outer housing 2 is partitioned into an upstream zone 9a and a downstream zone 9c downstream of a middle stream zone 9b by a diaphragm 17, and an inner cylinder 3 integrally incorporated with the center of the diaphragm 17 is slidably provided in the upstream zone 9a. A valve opening 13 formed between the middle stream zone 9b and the downstream zone 9c is made to be openable and closable by means of a relief valve 4 provided on the downstream side of the inner cylinder 3, and the relief valve 4 is urged in a valve opening direction by means of a relief valve spring 19. A first and a second check valve 5, 6 are provided in the inner cylinder 3 and the downstream zone 9c, respectively, so as to set the effective diameter of the diaphragm to a value substantially equal to the diameter of the valve seat of the relief valve, and the spring loads of the first check valve spring and the relief valve spring are set so that the pressure in the middle stream zone is held at a value which is always lower than the upstream pressure by a constant value.</p> |
