It’s inevitable to face issues concerning the valve control system and marine engineers are well-aware that it can literally happen anytime. The best way to determine whether or not there’s a problem with the control valve’s working condition is on-line. It can be very challenging to work on these things especially if they’ve been disregarded for a long time. To help you fix these problems as quickly, here’s what maritime folks experience with the control valves:
Problem #1: Valve Measurements
There are different measurements to each valve and the size mostly depends on a process design, not to mention its safety factor. The valves must be precisely in tune with the specifications but, more often than not, this is not the case which results in faulty use of the pneumatic valve control system. Sometimes, marine engineers discover undersized valves which can result to control loops and this doesn’t respond well to bottleneck and automatic processes.
If you want to know if the valve measurements are incorrect, use the controller to conduct a couple of output changes. It has to be in manual mode or you can use setpoint changes in automatic mode. Execute a minimum of two process changes and make them larger for the better. What’s more, you might need to change the entire valve or just the trim of it although it depends on what type. For large correcting units and out of balance forces, use the electric hydraulic control valve.
Problem #2: Stiction
This occurs when the valve is difficult to move from a standstill position. It’s generally the result of the overall static friction within the moving parts of the valve and other factors such as the viscosity of the process fluids, plug and seat properties, and the torque of the packing gland. You can observe this through the control loops in automatic mode. If you see square patterns in the process variable and jagged lines in the controller output, it’s stiction. To solve this problem, make sure that the valve positioner and actuator are both measured precisely, the air supply must conform to the manufacturer’s recommendation, and check the torque.
Problem #3: Hysteresis and Backlash
Loose and tattered linkages amongst the actuator, positioner, and the valve are the reasons for hysteresis and backlash. These things make the valve and other parts connected to it lag and lose their motion. To know whether this is happening to the control valves, observe the control loops in automatic mode. You’d be able to see it here but it won’t show you the immensity of the problem at hand. You can also put the control loops in manual mode for alternative. When this problem happens, the controller response also becomes slow and notice the rising patterns in the output.
Here are the three common problems that marine engineers have to deal with every now and then. It’s best to do a couple of tests and detect any of these problems before it gets worse so that things can be a little easier. What do you think of these problem encounters?