Background: Terminal Inlet Valve Bypass
Plant setup can vary depending on plant design, geography and size. A plant setup with a reaction turbine and penstock usually features two components:
- Turbine Inlet Valve (TIV)
- Turbine Inlet Valve Bypass
The TIV, also known as a guard or shutoff valve, prevents or allows water from entering the turbine. The Turbine Inlet Valve Bypass is installed on the downstream end of the penstock before the turbine. Although the TIV Bypass spends most of its time in the closed position as a low-duty cycle application, it still plays an important role in the startup sequence with the TIV. During startup, before the TIV can be opened, the TIV Bypass opens to equalize pressure upstream and downstream of the TIV.
The TIV Bypass employs different valve and actuator technologies and integrates within the TIV body itself in some configurations. Actuator types can differ between electro-mechanical, hydraulic, and even manual operation for smaller plants.
An imbalance of pressure between both sides of the TIV can wreak havoc on any unit with turbines experiencing turbulence, cavitation and mechanical shock/fatigue. Consequently, this reduces the life of the equipment and can even completely disable it. The greater the pressure delta – the greater the risk, which makes the TIV Bypass a critical part of the startup sequence to equalize pressure.
Both electro-mechanical and electro-hydraulic actuators can cause problems when actuating a TIV Bypass. Electro-mechanical actuators cause sticking, which means the valve either intermittently gets stuck or is jammed in place. Gearing within these actuators can cause gradual wear, leading to slop and possible valve “floating”. Similarly, electro-hydraulic actuators are susceptible to different forms of contamination including entrained air, oxidation, water, and more.
Therefore, plants should consider REXA Electraulic™ actuators for their TIV Bypass systems. Read more about our reliable solution for Turbine Inlet Valve Bypass in the full Application Spotlight below!