US Patent 9273535 Hydraulic flow restriction tube time delay system and method

A hydraulic time delay system and method in a wellbore tool is disclosed. The system/method includes an actuation mechanism which allows pressure to act on a functional piston in the wellbore tool. The movement of the piston is restrained by a partially or filled reservoir which is allowed to exhaust through a flow restriction element. The restriction element comprises standard metal tubing with a known inner diameter and is cut to an exact length as predicted by fluid dynamic modeling. A time delay and rate of piston movement desired for the downhole tool, between a trigger event such as pressure and a functional event, can be tuned with parameters that include the length and diameter of the tubing, reservoir fluid viscosity and number of tubes in parallel. In another embodiment, a secondary plugging element added to the reservoir controls the rate of piston movement and time delay.