The Block II provides a SOLUTION to servo strainer plugging and servo valve replacement WITHOUT interrupting turbine operation.
The BLOCK II consists of two major subassemblies: the duplex servo strainer and the hydraulic isolator.
DUPLEX SERVO STRAINER
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 II 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 II.
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.
A visual clogging indicator mounted on The BLOCK II manifold provides a visual indication of the condition of the filter in service. The clogging indicator also includes a 50 psid pressure switch that can be wired to a remote alarm.
The other sub assembly of The BLOCK II 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 II. 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 II 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 II 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 II.
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 II 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 II that allow either pressure gauges or vent lines hoses to be attached to visually check for pressure.
Block II INSTALLATION
The Block II is installed on an actuator by simply removing the servo valve (and its adapter plate if so equipped). The Block II 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.