Valve Replacement Provides Failsafe Feature with Rapid Installation

Bennett Engineering Services teamed with SOAR Hydropower on this design-build project for the City of Santa Barbara. The project included replacement of the existing penstock turbine bypass/outlet system.

The existing turbine bypass valve was a 12-inch Dezurik Eccentric plug valve with EIM hydraulic operator rated for 285 psi.  With a manual handwheel but no failsafe feature, the existing valve would have experienced severe cavitation and eventual valve destruction if used for the hydropower system without a fail-safe feature.

The valve selected to replace it is the Pratt Plunger valve with hydraulic close and counterweight open.  This provides a failsafe open feature in the event of a power failure or emergency.  The selected valve is to be equipped with a hydraulic cylinder that will operate at a pressure between 400 psi and 450 psi to match the existing HPU. Since the existing bypass system is used for water supply, it cannot be taken out of service for an extended period of time.  This requires a plan for valve replacement that can be completed within eight hours.

The design for installation of the new Pratt valve includes a Baker Style 602 Flanged Coupling Adaptor (FCA) designed for a working pressure of 300 psi.  The design of the FCA provides for telescoping a portion of the fitting over the existing steel pipe which allows room to more easily dismantle and reassemble the flanged pipe.  The FCA also provides for thrust restraint.

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