I'm working on one power plant we have GE 9FA gas turbine. I notice in the device summary for the servo valves GE tag number sometimes the start with 90 and some times start with 65.
90SR-1 >> STOP/SPEED RATIO VALVE SERVO VALVE
65FP-1 >> LIQUID FUEL PUMP (BYPASS VALVE) SERVO VALVE
but in the field it looks same
so any body have idea what is the difference?
The "90" and "65" are NEMA device numbers that are based on the functional purpose of the device. "65" is a governor device, "90" is a more generic control device. They have no meaning as far as the servo valve hardware. What does matter is the part number of the device. If the part numbers (GE drawing numbers) are the same, they should be interchangeable.
GE and its packagers have used a modified version of the ANSI Device Numbering system for the devices used on a heavy duty gas turbine. This system uses a one- or two-character device number for different types of sensors; a 26 device is a temperature-sensing device; a 63 device is a pressure-sensing device; a 59 device is an over-current sensing device.
A 65 device is a governor device, and a 90 device is a regulating device. 65FP-1, the liquid fuel bypass valve, is a fuel control valve and fuel is used to control speed and load. 90SR-1 is the Stop/Ratio Valve (SRV), who's primary function is the gas fuel stop valve, but who's secondary function is to control the pressure between the SRV and the GCV (Gas Control Valve)--the P2 pressure.
So, the device number describes the function not the type of device. It might be a Moog electro-hydraulic servo-valve, it might be a pneumatic control element, it might be a three-coil servo valve or a two-coil servo-valve, the two servo-valves might even have different manufacturer part numbers. For example,771GK208 and 771GK200A are two Moog servo-valves which look identical from the outside but have different flow-rate characteristics.
Some GE-design heavy duty gas turbines use the same Moog servo-valves for some or even all of the servo-operated devices, but some don't. It's not good to presume that if the servo-valves look identical they are identical.
Hope this helps!
It's just a difference in the interpretation of the ANSI numbering system that GE use for devices.
A 65 device is classified as a "Governor" device (The assembly of fluid, electrical,or mechanical control equipment used for regulating the flow of water,steam, or other media to the prime mover for such purposes as starting, holding speed or load, or stopping)
A 90 device is classified as a "Regulating" device (A device that functions to regulate a quantity or quantities,such as voltage, current, power, speed,frequency, temperature, and load, at a certain value or between certain (generally close) limits for machines, tie lines, or other apparatus.)
The above definitions are from an ANSI Numbering system document.