INTRODUCTION
The gas over hydraulic actuator is designed and used for the operation of quarter turn valves (ball valves and plug valves) installed on gas transportation lines, in compressor stations and everywhere a high pressure gas supply is available.
The gas over oil is composed of one or two double action hydraulic cylinders that, pressurized, determine the linear motion of the piston contained in it. The linear motion of the piston is transformed into rotation by a scotch yoke mechanism.
Gas sampled by the line, pressurizes oil contained in one of the two gas-hydraulic tanks and then the one of the cylinder determining the drive of the actuator.
A peculiar feature of gas over oil actuator is its great flexibility of use obtained by the choice of a manufacturing solution easy, solid and without parts in motion.
FEACHURE
- Actuators operating at different pressures are available upon request.
- Varieties are offered depending on geographical requirements, engineering works and site conditi
- Gas over oil tanks separate the feeding gas from the hydraulic cylinder.
- Canted or symmetric scotch yoke design achieves high break torque for operating all kinds of quarter-turn valves.
- Automatic control groups for the actuator operation (in opening or in closing) are also available. Such as: ON-OFF, Line Break Valve (LBV), Emergency Shut Down (ESD), Electrical Fail Safe (EFS) and Liquid Line Break Valve (LLBV).
TECHNICAL DATA
- Design Pressure : Up to 105 barg
- Supply Medium : Sweet or Sour high pressure gas, Nitrogen or Instrument Air
- Output Torque : Up to 750,000 Nm
- Ambit Temperature (Standard Range) : –29°C to +80°C
- Ambit Temperature (Extend Range) : –60°C to +180°C
GAS OVER OIL ACTUATOR AUTOMATIC CONTROL GROUPS
LBV AUTOMATIC CONTROL GROUPS
The standard Line Break Valve “LBV’’ control is completely autonomous, not depending on other power/control sources.
The Line Break Valve “LBV’’ device automatically closes the actuator when the pressure drop rate exceeds a preset value.
Special versions of Line Break Valve ‘’LBV’’ control for sour gas, liquid fluids, dirty and very humid natural gas are also available.
ON-OFF AUTOMATIC CONTROL GROUPS
AIV can supply different types of control systems following customer requirements AIV has produced a wide range of pneumatic and hydraulic components specifically engineered to suit the most varying needs of the customer (i.e. control mode, emergency operation, working temperature range, pressure range of the gas supply etc.).
These components guarantee a high reliability and compact design.
Every pneumatic valve is engineered to work with high pressure gas.
Therefore the control group does not need to be fed by means of a pressure reducer. In this way the reliability of the system is increased.
The pneumatic valves in aluminum alloy are poppet type in order to provide bubble tightness. The sealing seats are made of Teflon, thus granting chemical resistance, lack of sticking and aging effects and the highest compatibility with every environment condition.
The basic control system of the AIV gas-over-oil actuator mainly consists of a double 3-way 2-position control valve, which is normally piloted by 2 solenoid valves for remote control, one for closing and one for opening. It is also possible to locally operate this valve by means of 2 levers, one for closing and one for opening.
ESD AUTOMATIC CONTROL GROUPS
The Emergency shut Down "ESD" device automatically opens or closes the actuator when the pressure or the pressure value is outside the normal range of values.
The pressure switch can either be pneumatic or electric.
EFS AUTOMATIC CONTROL GROUPS
The Electrical Fail Safe “EFS” control signal is also present at the end of the maneuver like for the "ELECTRIC FAIL SAFE" system and for the "ESD" device, the actuator can be provided with pneumatic limit switches which cause the exhaust of the gas used for the operation at the end of the actuator maneuver.
In this way the gas-over-oil tanks and all the hydraulic components are only pressurized during the actuator operation.
LLBV AUTOMATIC CONTROL GROUPS
The Liquid Line Break Valve “ LLBV” control group effects of orifice diameter, pipeline initial pressure and pressure drop rate due to rupture on the differential pressure of diaphragm valve in an automatic line-break control valve have been studied by experiments. The fluid in this experimental investigation was nitrogen. The Accumulator Ball type is connected to the pipeline through a calibrated orifice with check valve. The Accumulator pressure is higher than pipeline pressure when pressure reduction occurs by line breaking. If the pressure difference between Accumulator and pipeline is higher than the sustainable pressure value of diaphragm valve, the valve will be closed by actuator. The differential pressure of diaphragm valve is increased by the growth of pipeline pressure drop rate. The occurrence time of maximum differential pressure of diaphragm valve just depends on the orifice diameter. The maximum of differential pressure increases with the decrease of orifice diameter. The setting differential pressure of control valve was increased by decrease of pipeline initial pressure or orifice diameter or increase of pressure drop rate.
