The application required the production of Heavy Duty Electro-hydraulic actuators with repositioning of the valve in the safety position (closed).
The operation required the intervention of the TruTorq technical office both for the mechanical construction of the hydraulic actuator, and for the selection and combination of devices necessary for the control of the actuator's activity.
There was no source of pressurized fluid on the system to serve as a power supply for the actuators, only an electrical power supply. In addition to this limitation, the application also required that, in the event of a power supply failure, the actuator would activate to return the valve to safety conditions.
In addition, the maneuver to return the valve to the safety position could not be compliant with the operating times: 90% of the motion of the valve from 90 degrees (Fully open) to 0 degrees (Fully closed) had to be made in 6 seconds while the remaining 10% in 14 seconds so as to prevent excessive compression of the fluid managed by the valve. The unit also had to be able to be controlled Remotely and Locally.
The solution proposed by TruTorq was to utilize Scotch Yoke Heavy Duty actuators (due to the high torque of the valve) in the Electro-Hydraulic version. This type of actuator offered a solution to the first two critical issues that emerged. In fact, the unit is composed of a single acting hydraulic actuator with spring return, which enables the repositioning of the valve to a safety position in the case of an emergency.
The actuator was equipped with a dedicated hydraulic power unit, which performs multiple functions:
- Converts the electric power supply to a hydraulic power supply via the motor and pump it is equipped with;
- Allows the management of the actuator operating command by means of solenoid valves through which the hydraulic fluid passes.
- The control unit was also equipped with a manual pressure system by means of a manual pump that can replace the motor in special cases.
To allow the management of commands both remotely and locally, TruTorq designed an electronic panel that allows different functions:
- Connect with the DCS control cables (remote control);
- Bypass the command from DCS to allow the operator on the system to be able to operate locally, through a selector directly mounted on the panel.
- Diagnosis of the operating conditions of the actuator, sending anomaly signals to the DCS in the event of non-optimal conditions (e.g. motor temperature too high, oil level too low, failure to detect the reference position switch within an established period of time following the command).
The only remaining critical issue was the management of the two different operating speeds during valve closure.
For this specific case TruTorq designed a hydraulic cylinder dedicated to the application, creating a second chamber inside the cylinder relative only to 10% of the stroke, where the discharge of the hydraulic oil is reduced so as to slow down the maneuver by the specific percentage requested by the customer.