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Hydraulic Power Control Units

IMI Remosa's Hydraulic Power Control Units are designed in accordance with the most stringent process licensor specifications and international standards.

Actuators and Hydraulic Power Control Units are designed to provide the valve with the desired action. As standard, actuator, hydraulic power unit and control unit will consist of the following:

Actuator Mechanical Drive Section

  1. Hydraulic piston
  2. Mechanical drive section case
  3. Manual drive
  4. Worm gear-motor
  5. Clamp lock assembly
  6. Manual drive engaging/disengaging system
  7. Adjustable limit stops
  8. Stem anti-rotation device
  9. Mechanical position indicator (double reference scale)
  10. Redundant position transmitters
  11. Valve closed position switch
  12. Pneumatic motor
  13. Lifting lugs

Hydraulic Power and Control Unit

  1. Two electrical driven oil pumps: primary and stand-by
  2. Two hydraulic filters
  3. Hydraulic reservoir
  4. Main accumulators
  5. ESD accumulators
  6. Manual hydraulic operator
  7. Servo-valve manifold
  8. ESD circuit manifold
  9. All instrumentation, valves and piping necessary for Unit operation
  10. Cylinder isolation manifold
  11. Local (or remote) panel with a control system for alarm and monitoring signals data acquisition and position control, and a Human-Machine-Interface (HMI) for alarm and variable indications for all actuator and hydraulic power unit monitoring parameters
  12. Back-up control system (jog-control)
  13. Air/oil cooling/circulation and filtration system

Final configuration for actuator, hydraulic power unit and control unit could differ from the above description to comply with all the applicable project specifications.

The electro-hydraulic actuators are always designed in compliance with all the applicable project specifications. In details:

Actuator set components will be designed to support environmental temperatures during operation.

Stroking time from the fully-closed position to the 100% open position will be in accordance to project specifications. The actuator nominal thrust, as standard, is 200% over the required thrust.

Fail safe mode: according to valve data-sheet.

Main accumulators: hydraulic power accumulator, piston type, Viton® seals, to provide hydraulic fluid for a minimum of two full strokes based on maximum travel and normal operation thrust with a thrust safety factor of two.

Stand-by (ESD/Reserve) accumulators: hydraulic power accumulator, piston type, Viton® seals, to provide hydraulic fluid for a minimum of two full strokes based on maximum travel and normal operation thrust with a thrust safety factor of two.

Oil reservoir: is sized to provide enough capacity for two times all accumulators, cylinders, manifolds and piping.

Electrical pump: are sized to allow 10% of total stroke in 5/10 sec max once main accumulators have been disconnected.

Electrical motors will have corrosion protection.

Electrical power, climatic ambient temperature range, electrical and electronic classification: according to project specifications.

All electrical systems protection degree will be IPW-65.

Highly ergonomic design for HPCU and mechanical actuator is chosen by Remosa to allow easy operation and maintenance.

Operating modes

In hydraulic mode the double effect cylinder receives high pressurized oil from a port (C1 or C2), while the other port allows the oil discharge from the other side of cylinder. The differential pressure between the two hydraulic cylinder cameras generates the thrust required to move a valve disc.

To work in mechanical mode every hydraulic function needs to be disabled; it is also necessary to manually engage this mode in order to avoid any chance of hydraulic and mechanical contemporary use. The system engagement is made by rotating the engaging lever; once rotated, two bronze split nuts clamp an ISO screwed bar and the clamp lock assembly starts moving according to the screw rotation.

Once engaged the mechanical drive, the field operator can manouver the actuator by a rotation of the actuator handwheel or by the pneumatic motor.

The worm gear-motor will run in lubricant medium and will be sealed by Viton® type material seals.

Hydraulic design features

All the main components (HPCU frame, oil reservoir, valves, etc) are manufactured on stainless steel SS304L or SS316L.

Pipe, pipe fittings and isolation valves will be flanged or socket welded constructed in 316L SS, with size and schedule suiting the system design pressure.

All pressure instruments are provided with block and bleed manifold. All electronic transmitters (pressure, differential pressure, temperature and level) are Hart 4-20mA output type: discharge pump A pressure transmitter, discharge pump B pressure transmitter, filters differential pressure transmitter, main accumulator pressure transmitter, oil reservoir level transmitter, oil reservoir temperature transmitter, cylinder close side pressure transmitter, cylinder open side pressure transmitter, lock-in-place test pressure transmitter.

Two variable displacement, axial pistons hydraulic pumps are provided. Each pump is provided with pressure transmitters at discharge side and a pressure transmitter downstream the hydraulic filters to monitor main hydraulic system pressure.

Standby pump starts up automatically in case of main pump failure. Interlock is provided to prevent pump and air cooling system operation in the event of no hydraulic fluid in the reservoir. A skid grounding system has always provided.

Electrical motors (provided) are certified according to project specifications.

An air-oil cooling system is installed to allow an oil temperature control during operation.

Hydraulic filters are designed for the full differential pressure of the pump discharge. A differential pressure indicator and alarm is supplied across the filters. Changing filter elements does not result in a loss of main hydraulic fluid system pressure.

All accumulators are provided with isolation and bleed valves. Bleed valves are permanently connected to the reservoir.

The hydraulic reservoir is provided with a thermometer, temperature transmitter, level gauge and level transmitter. Drain valve and provision for clean out are provided on the oil reservoir.

To allow for manual hydraulic operation, a manually operated shutoff valve to isolate the servo-valve from the hydraulic system and close the pilot operated check valves (POCV), and a manually operated 3-position valve (open-auto-close) are provided.

IMI Remosa installs jet-pipe style servo-valve, the best available in the market for this critical application, less sensitive to dirt than standard nozzle/flapper style servo-valve. The servo-valve can be isolated and removed for repair without depressurizing the hydraulic system.

Electronic design features

Position control is implemented in the digital control system and fulfils the following performance requirements:

  1. Input and output signals: 4-20 mA, DC
  2. Valve closed: 4 mA
  3. Valve opened: 20 mA
  4. Stroking requirements: adjustable speed
  5. Design stroke: according to project specifications
  6. Design speed: according to project specifications
  7. ESD speed: according to project specifications
  8. Continuous: 10% of stroke in 5/10 seconds (for pump sizing only)
  9. Step resolution, dynamic response, dead band, transient overshoot, stability, repeatability, linearity in compliance with the requirements of project technical specifications.

Cable interconnection between field instruments and the local (or remote) control system are accomplished by means of a dedicated terminal strip, properly located, and with available space to allow easy access of maintenance personnel. The terminal strip are also mechanically designed to allow easy connection, disconnection and handling of cables in the field.

All signals related to lock in position logic (Low low main hydraulic system pressure, HPU instrument power loss, electronic failure, manual gear mode selected, hand-wheel engaged, position signal failure and control signal failure) lock the valves in last position (high deviation alarm as standard is not a lock in position cause).

IMI Remosa installs as standard a local operator interface for field operation. The local panel is certified according to the area classification of the unit. Local panel incorporates protections against rain and dust exposure according to IP-65 code. All alarms/shutdown indications, auxiliary and monitoring systems variables are available on the local panel.

Actuator trouble alarms configured at local panel include:

  • Loss of control signal
  • Loss of tracking (deviation alarm)
  • Position signal failure
  • Power supply failure

Hydraulic system trouble alarms configured at local panel include:

  • Low pressure at pump A discharge
  • Low pressure at pump B discharge
  • Low low level at reservoir
  • High high temperature of hydraulic oil
  • High differential pressure at filters
  • Low pressure at main accumulator

The following indications are also configured at local panel:

  • Slide valve position
  • Position control signal output
  • “Hand-wheel engaged”
  • Pumps running
  • All indications from transmitters specified for the actuator system

A local digital control system (with serial link to the DCS, i.e. Modbus-RTU via RS-485) is provided for the actuator sub-system variables data acquisition, alarm handling, position control and drive automatic start-up of stand-by equipment.

All control and interlock signals are transmitted hardwired to DCS.

All the components, such as servo-valves, transmitters/transducers, limit switches, solenoid valves, are explosion proof Ex'd or intrinsically safe Ex'i or encapsulation Ex'm certified (and not components for safe area encapsulated in explosion proof housing).