Abstract
In a semi-closed pipeline system, if the water diversion stops or if it is diverted at 20% or less of the design flow rate at a decompression system with a disk value vibration, called chattering of disk, can occur at the small opening, and often cause a strong water hammer. The placement of an oil damper between the float and the balancing arm is considered to effectively prevent the chattering. Even if a sudden pressure change occurs in the pipe conduit, the oil damper temporarily absorbs it or reduces the vibration of the disk valve by dissipating its kinetic energy and thereby making the motion of the float less sensitive. This paper presents a rotational vibration model of the disk valve system with a built-in oil damper, and numerically investigates the effects of such a system on transient flow in the whole pipeline system. As a demonstrative example, the methodology presented is applied to a real pipeline system with 8 disk valves. Computational results indicate that the chattering can successfully be suppressed by use of damper, but the water hammer caused in stopping water diversion cannot significantly be reduced. It is therefore concluded that even in the system equipped with the damper an additional capacity (say, corresponding to 3 min × design flow rate) should be provided in a decompression tank to eliminate the water hammer.
