The flanged pneumatic cut-off valve cannot be opened properly
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I would like to ask everyone for advice regarding a problem that has been occurring frequently in our company recently: it’s a flanged pneumatic ball valve with a nominal diameter of DN40 and PN16; the actual diameter is 25 mm. The actuator used is SR83-10, the operation type is FC, the stroke is 90 degrees, the nominal pressure is 1.6 MPa, and the air supply pressure is 500 kPa. The installation height of this valve is 7.5 meters; the pump is located on the ground, and the gauge pressure generated by the pump ranges from 0.2 to 0.35 MPa. There is no bypass pipe. The procedure involves starting the pump first, followed by opening this pneumatic ball valve; however, it fails to operate. The pressure of the regulator was set to 0.65 MPa, but the valve still cannot be opened properly. Excuse me, what’s going on here? What are the reasons for it?
First, it is necessary to determine whether the problem lies with the valve body or the actuator; inspection must be carried out in stages. First, a manual action signal is sent as a whole to determine whether it is a problem with the control signal or with the actuator. A check of the third section in the branch plant can identify the problem. Additionally, the operating temperature of the valve must be appropriate and within the specified range, as the valve seats of many ball valves are made of PTFE, and it is necessary to confirm their heat resistance rating.
Confirm what the maximum opening pressure of the valve is, and what torque should be selected for the actuator; generally, this torque is around 1.2 times the torque required to open the valve. If signal issues are ruled out, it is likely a problem with the valve selection.
I’m not quite sure – if the cylinder is marked as FC, it means it’s normally open. Then you say that the valve needs to be opened right after the pump starts? Normally, the valve is open even without venting; I suspect that the solenoid directional valve might be installed in the wrong direction. If there is no ventilation, the valve status is.
Yes, normally closed; it opens when ventilation starts and closes when ventilation stops
Under such operating conditions, there should be no problem with a pneumatic actuator of this specification paired with a ball valve of this diameter. There are probably 3 reasons: 1. The valve issue – the valve is stuck, resulting in excessive torque. 2. The pneumatic actuator problem – air is leaking inside the cylinder, preventing the desired torque from being achieved. 3. Is there an issue with the air circuit controlled by the solenoid valve?
Well, if it’s normally closed, you can try connecting the air supply directly to the inlet of the cylinder to see if it can be opened. If it opens, then the problem lies with the solenoid valve or with the installation direction. For single-acting cylinders, some come equipped with a single-acting plate; it’s also possible that the direction of this plate is incorrect. I’m not sure what type of cylinder you have. If that still doesn’t work, it’s either because the valve is stuck or the actuator is too small. But in theory, when the air pressure is increased to 6 bars, the valve should be able to move at least a little, unless the selection was very poor; so it seems like the problem lies with the solenoid valve.
By opening the valve on the pump-out return pipe (which is actually the pathway during unloading) to a certain degree, and after several days of operation in online mode, if this valve resumes its normal opening and closing behavior, then a question arises: Does the pressure in the pipeline exert some axial force on the closed valve ball, or is there a combination of axial and radial forces? Can this force prevent the valve ball from moving properly? Is there any mechanical analysis in this regard?
By opening the valve on the pump-out return pipe (which is actually the pathway during unloading) to a certain degree, and after several days of operation in online mode, if this valve resumes its normal opening and closing behavior, then a question arises: Does the pressure in the pipeline exert some axial force on the closed valve ball, or is there a combination of axial and radial forces? Can this force prevent the valve ball from moving properly? Is there any mechanical analysis in this regard?
1. The pressure of the medium flowing through the pipeline does indeed affect the opening and closing of the valve, especially for media with a high viscosity coefficient. 2. The valves and actuators of this diameter selected should not have any major problems when used with a water-based fluid at 0.6 MPa. However, when there is an adequate budget, it is still advisable to apply a higher safety factor for single-acting actuators; choose AT92 cylinders in such cases