Due to their design, electric actuators have limitations in terms of output torques, duty cycle, failure modes, speeds, and vibration resistance.  

In severe applications where valves with high torque or thrust must be operated quickly, such as emergency shutdown valves (ESDV), electric actuators have limitations because they can only store a certain amount of energy to operate the valve in the event of a power failure, which eliminates them as options in many emergency shutdown valve applications. In the same way, because they are operated directly by an electric motor, they present limitations in the operating speed; on one hand, the demand increases significantly as the speed increases and on the other hand, their operating speeds are constant since they depend on the RPMs of the motor, so if variable speeds are needed, these actuators are not a practical option.  

Electro-hydraulic actuators while using electrical energy to operate, transform this energy into hydraulic energy which is used to operate the valve, for this reason they are able to provide significantly higher thrusts or torques, high stored energy capacity in case of failures and operating speeds not only significantly faster, but with the flexibility to be adjusted to provide variable speeds.  

Cowan Dynamics offers a wide range of electrohydraulic actuators in its EH series. Electrohydraulic actuators for linear, rotary, isolation, or control valves. We offer actuators specifically designed for emergency shut-off valves (ESDV).