Troubleshooting of Copes Vulcan bypass valve

Replace traditional thermocouple temperature feedback with algorithmic temperature control (ATC) (see Part 6 for details).

If there is a severe fluctuation in the outlet temperature on site, first check the linearity of the action of the cooling water valve, and then confirm whether the correct inlet pressure and temperature signals are used for calculating the steam enthalpy value in the ATC logic.

Common debugging problems of PRDS and TE-PRDS temperature and pressure reduction stations

PRDS and TE-PRDS valves are widely used in auxiliary steam systems or industrial steam supply pipelines. Typical faults include:

4.1 Cage type guide valve stem jamming

When the steam cleanliness is poor or rust is generated during shutdown, the gap between the valve core and the cage sleeve (usually 0.15~0.25mm) may be stuck by hard particles, causing the valve to fail to operate or operate slowly.

On site emergency response:

In the shutdown state, inject specialized cleaning solution (such as a mixture of kerosene and penetrant) from the valve body discharge port, soak for 12 hours, and then repeatedly move the valve stem.

If it still gets stuck, the valve cover needs to be removed, and the throttle cage sleeve needs to be removed for grinding or replacement (pay attention to the thickness of the chrome plating layer).

4.2 Water droplets sprayed from the cooling nozzle are not completely vaporized

Manifested as water accumulation at the bottom of downstream pipelines, even causing water hammer. The main reason is that the steam flow rate is lower than the minimum atomization speed (generally required to be 25-30 m/s); Or the nozzle installation position is too close to the temperature measurement point.

Countermeasure: Recalculate the number and aperture of nozzles based on the design flow rate; Ensure that the length of the straight pipe section after the temperature reducer is not less than 10 times the diameter of the pipe.

4.3 Selection of throttling components and excessive noise

When the pressure difference before and after the PRDS valve exceeds 100 bar, if multi-stage pressure reducing components are not used, the noise can easily exceed 110 dBA. On site inspection should be conducted to ensure that the valve internals are HUSH multi-stage orifice plates. If it is a regular balance plug, it can be considered to be modified into a 3-5 stage throttling sleeve, with each stage's pressure reduction ratio controlled between 2-3.

Selection and troubleshooting of pneumatic and electro-hydraulic actuators

The actuator is the core of the dynamic response of the bypass system. Copes Vulcan offers two solutions, pneumatic and electro-hydraulic, each with its own advantages and disadvantages in practical operation.

5.1 Pneumatic actuator - rapid response transformation

Standard pneumatic diaphragm or piston actuators often require 5-10 seconds of full stroke time due to air capacity limitations, which cannot meet the requirement of fully opening in 2 seconds during machine trip. On site, the time can be shortened to 1.5-3 seconds by installing a pneumatic accelerator (Booster) and a quick exhaust valve.

Fault phenomenon: The actuator operates slowly, with a step response time greater than 2 seconds.

Inspection steps:

Measure the minimum pressure of the gas supply pipeline (should not be lower than 5 barg).

Check if the filter in front of the accelerator is clogged.

Manually operate the quick exhaust valve and confirm that the valve can instantly release the pressure on the other side of the cylinder.

If all of the above are normal, consider the wear of the piston seal ring (gas leakage) and replace the seal.

5.2 Electro hydraulic actuator HPU system

Common faults of centralized hydraulic power unit (HPU):

Frequent pump start-up: The accumulator bladder is damaged or the nitrogen charging pressure is too low, resulting in a short holding time. Under normal operating conditions, the pump should be started every 1-2 hours to replenish leaks; If it is started every 10 minutes, it is considered that the accumulator has failed.

Excessive oil temperature (>60 ° C): scaling of the cooler or excessive viscosity of the oil. Phosphate ester fire-resistant oil is temperature sensitive and will accelerate decomposition beyond 55 ° C. The oil/water heat exchanger should be cleaned regularly.

Large pressure fluctuation: The pilot stage of the servo valve is blocked. It is necessary to disassemble and wash the servo valve (replace the filter element), and install a 10 μ m absolute filtration precision filter at the outlet of the oil pump.

5.3 Self contained electro-hydraulic actuator

Common problems with integrated electro-hydraulic actuators (including motor, oil pump, oil tank, and accumulator) directly installed on valves:

Frequent motor start stop: severe internal leakage, mostly due to piston seal or one-way valve leakage. After manually pumping, observe the pressure drop rate. If the drop exceeds 5 bar per minute, it needs to be disassembled for inspection.

Unable to operate manually: The check ball valve in the manual pump is stuck or the pump is short of oil. Add fuel and repeatedly pump the handle to release air.