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Steam Turbine High Pressure Fluid System Upgrade Products

The Block IV

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Block IV is a device that can easily be added to a servo controlled hydraulic actuator. It provides duplex filtration for the servo pilot supply. This allows for on-line changing of the filter without the need for isolating the servo valve. The duplex filter assembly incorporates a differential pressure reading with a built in alarm that provides immediate feedback on the condition of the active Block IV filter. The inactive Block IV filter can be removed, cleaned or replaced with the unit on line without having to isolate the servo valve or reduce load on the unit.

The Block IV also allows for complete hydraulic fluid isolation of the servo valve with the unit online. There are three pressure test point on The Block IV that assure the servo has no pressure on it prior to its removal. This feature is a significant improvement over the current GE design which makes removing the servo valve much safer.

Real time hydraulic diagnostics are integrated into the Block IV. The variables monitored by the Block IV include:

  • Servo Valve Flow Rates (gpm)-this provides an ongoing condition of the servo valve which aids in determining whether or not a servo valve needs to be sent out for repair during a scheduled outage. The Block IV is capable of accuratly reading servo flows as low as 0.5 gpm. An alarm occurs after 60 seconds of operation above 1 gpm.
  • Digital servo filter differential pressure (psid)-this provides an accurate condition of filter plugging without having to wait for an alarm to occur. A 50 psid alarm is
  • incorporated into the monitoring circuitry.
  • Indication of pressure before the servo valve (psig)-this indicates whether the
  • components ahead of the servo valve are functioning properly (Fast Acting Solenoid, Shut-Off Valve and Disk Dump Valve).
  • Indication of pressure after the servo valve (psig)-this indicates the pressure under the hydraulic actuator. When plotted against actuator lift (hysteresis curve) an accurate determination can be made regarding the overall mechanical condition of the hydraulic actuator which will aid in determining when an actuator needs to be sent out for repair.

The Block IV diagnostic signals are sent to an optional HMI display that is located in an electrical enclosure which is mounted in the general area of the steam valves, Located within the electrical enclosure is an Ethernet/Modbus connection which provides a digital signal of all of the above diagnostics which can be transmitted to the control room for remote data logging, trending and archival purposes.

The BLOCK IV consists of two major subassemblies: the duplex servo strainer and the hydraulic isolator.


The Duplex Servo Strainer consists of a 3-way filter selector valve, two (2) cartridge type 40 micron Beta 200 removable filters, a visual clogging indicator with a built in pressure switch alarm and three check valves all mounted on an aluminum manifold. The 3-way filter selector valve is equipped with a safety cover.  The safety cover helps prevent an operator from inadvertently removing a filter from a pressurized cavity.

The BLOCK IV is designed to mount between a 25 GPM Abex model 425 or Moog model 743 servo valve and a steam turbine valve actuator manifold.  The jet (pilot) supply fluid is obtained from the pressure port of The BLOCK IV.

Note:  If the installation uses a jet supply line (FJS) from the hydraulic power unit, then this line may be capped or removed after installing

Jet supply fluid passes through the 3-way filter selector valve and into one of the filters.  The 3-way filter selector valve is designed such that pressurized jet supply fluid is always supplied to the servo valve when transitioning from one filter to the other.  Clean fluid is then directed to the servo valve pilot supply port.  Zero leakage, poppet type check valves located downstream of each filter allow the operator to service the off-line filter while the other filter is on-line.


The other sub assembly of The BLOCK IV is the Hydraulic Isolation valve which allows for the complete removal and replacement of the servo valve with the unit on-line. This includes isolation of the system drain line without compromising normal system operation

In order to isolate all of the hydraulic fluid from the servo valve, the main fluid supply, jet supply and system drain to the servo valve must be shut off with assurances that no pressure exists either to or from the servo valve.

In order to accomplish this task, the jet supply to the servo valve is provided from within The BLOCK IV. The existing jet supply (FJS) is no longer used.

On EHC systems shipped prior to 1980, GE offered an upgrade modification to allow for on-line servo isolation. Part of this modification (Servo Isolation Scheme) consisted of adding an adapter plate between the servo valve and the hydraulic actuator.  This plate is no longer needed since The BLOCK IV incorporates the functionality of this adapter plate.

On units shipped after 1980 GE either provided the adapter plate or drilled holes in the hydraulic actuator.  In either case, The BLOCK IV will eliminate the need for the plate and the drilled holes will have no effect of the servo valve following the Installation of The BLOCK IV.

By isolating the main pressure supply, which is also supplying the servo jet supply and the system drain, the servo valve is hydraulically isolated from the high pressure fluid system and can be safely removed.

The BLOCK IV incorporates a manual isolation valve, which is capable of completely shutting off all of the hydraulic fluid to the servo valve.

In order to verify there is no fluid pressure on any of the servo valve ports, a series of test points are attached to The BLOCK IV that allow either pressure gauges or vent lines hoses to be attached to visually check for pressure.


The Block IV is installed on an actuator by simply removing the servo valve (and its adapter plate if so equipped). The Block IV is then bolted to the actuator in place of the servo valve and the servo valve is then bolted onto the Block II. This task takes less than 15 minutes with the unit shut down and the hydraulic fluid system depressurized.

The electrical transducers can either be wired to the optional HMI enclosure or directly to the plant’s computer system.


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