Model Characteristics and Fault Analysis of 3-Way control valve

Model Characteristics and Fault Analysis of 3-Way control valve

April 22, 2019

The ZJHF(H) type 3-Way control valve produced and sold by Datian Valve has two modes of three-way combined flow and three-way splitting. In some cases, it can be widely used instead of two two-way valves and one three-way valve. The adjustment of pressure, flow, temperature, liquid level and other parameters is realized. The valve core structure adopts a thin cylindrical window of the cylinder and adopts the side guide of the valve core. The stability is good, the vibration is not easy to occur, the noise is low, and the pressure difference is allowed to be large. The line is simple and so on. When the nominal diameter and differential pressure are small, the confluence valve can be used for diversion occasions and can be used interchangeably. However, the nominal diameter is larger than DN100 and the differential pressure is large.

The three-way split regulating valve uses compressed air as the power source and the cylinder as the actuator, and drives the valve by means of electric valve positioner, converter, solenoid valve, retaining valve and other accessories to realize the switching quantity or proportional adjustment. Receiving the control signals of the industrial automation control system to complete various process parameters such as flow, pressure, temperature, etc. for adjusting the pipeline medium. The characteristics of the pneumatic regulating valve are simple control, fast response, and intrinsic safety. No additional explosion-proof measures are required.

Key inspection site during maintenance

  • Check the inner wall of the room: in the case of high pressure difference and corrosive medium, the diaphragm of the inner wall of the valve and the diaphragm valve are often subjected to the impact and corrosion of the medium, and the pressure and corrosion resistance must be checked.
  • Check the valve seat: the inner surface of the thread for fixing the seat is susceptible to corrosion and the seat is slack due to the infiltration of the medium during operation;
  • Check the valve core: the valve core is one of the movable parts of the regulating valve. It is seriously damaged by the medium. During the inspection, it is necessary to carefully check whether the various parts of the valve core are corroded and worn, especially in the case of high pressure difference. The cavitation caused by cavitation is more serious. Severely damaged spools should be replaced;
  • Check the sealing packing: check whether the packing asbestos rope is dry. If using PTFE packing, pay attention to check whether it is aging and whether its mating surface is damaged;
  • Check if the rubber film in the actuator is aging and cracked.

Daily maintenance of three-way control valve

When the regulating valve is made of graphite-asbestos, the lubricating oil should be added to the packing for about three months to ensure the flexibility of the regulating valve. If it is found that the packing pressure cap is pressed very low, the filler should be replenished. If it is found that the polytetrafluoroethylene dry packing is hardened, it should be replaced in time; pay attention to the operation of the regulating valve during the inspection, check whether the valve position indicator and out Analyze; check the gas source for the regulating valve with the positioner, and find the problem in time; always keep the health of the regulating valve and the complete and easy use of all components.

Three-way regulating valve failure phenomenon:

  • No signal, no gas source.
    1. Gas source is not open
    2. Because the water source contains water in the winter, the air duct is blocked or the filter is reduced.
  • There is a gas source, no signal.
    1. Regulator failure
    2. Signal tube leakage; 3. Positioner bellows leaking
    4. Adjust the mesh diaphragm damage
  • The positioner has no air source.
    1. Filter is blocked;
    2. Pressure reducing valve failure I
    3. The pipe leaks or is blocked.
  • The positioner has a gas source, no output.
    The orifice of the positioner is blocked.
  • there is signal, no action.
    1. Spool is detached
    2. Spool is stuck with the society or with the valve seat
    3. The stem is bent or broken
    4. Valve seat spool freezing or coke block dirt
    5. Actuator springs rust due to long-term use

The operation of the three-way regulating valve is unstable.

The symptoms and causes are as follows:

The pressure of the air source is unstable.

1. The compressor capacity is too small;
2. The pressure relief valve is faulty.

The signal pressure is unstable.

1. The time constant (T=RC) of the control system is not appropriate;
2. Regulator output is unstable;

The pressure of the air source is stable and the signal pressure is stable, but the action of the regulating valve is still unstable;

1. The ball valve of the amplifier in the positioner is not tightly damaged by dirt, and the output oscillation occurs when the air consumption is particularly increased;
2. The nozzle flapper of the amplifier in the positioner is not parallel, and the flap cover cannot cover the nozzle;
3. Output tube, line leakage;
4. The actuator is too rigid;
5. The frictional resistance is large in the movement of the valve stem, and there is a blockage in the contact part.

Three-way control valve range

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