Question regarding the replacement of V-ball control valves with single-seat control valves
Thread Content
PID control is used for the control valves that regulate gas flow rates; currently they are single-seat valves, and there is consideration to replace them with V-ball control valves. The control engineer said that the flow-openness curve of V-ball is too straight, raising concerns regarding control performance. Please give me some advice, thank you! Also, if this control valve is replaced with a V-ball valve, will it affect the stability of the upstream PID-controlled main control valve? The main control valve is now also a single-seat valve.
You need to examine the flow characteristic curves of both options and compare them to find out, but based on personal experience, I think your colleague is right; if spherical valves are to be used, other measures are required to offset the impact on flow
This post was last edited by Benbang Self-Acting Valve – Engineer Li on 2019-5-21 at 14:11. In terms of regulation performance, V-ball valves are indeed not as good as single-seat valves; however, one advantage of V-ball valves is that they perform better under high-pressure conditions and in harsh operating environments. Their cost is also relatively low. As we said, if rough regulation is sufficient, V-ball valves will do the job, but for precise regulation, proportional control valves are required! Of course, if a V-type ball valve is still to be used for adjustment, it is necessary to do some preparatory work beforehand: calculate the size of the opening in the V-shaped port of the ball valve. The more precise and detailed the calculation of the V-angle, the closer it will be to the curve that needs to be adjusted! As for whether a real replacement is necessary and what the impacts will be, it depends on the specific circumstances!
Thank you for your reply. The selection of the V-ball valve was based on the flow rate range of the original single-seat valve as well as the pressures before and after the valve; the flow-rate vs. opening curve was not checked
The selection of the V-ball is based on the parameters of the original single-seat valve; an opening degree of 45% to 80% for the V-ball is sufficient to cover the existing flow range, which corresponds to the area between the two vertical lines in the diagram below. Overall, it doesn’t seem to follow a curve with equal percentage increments. . .
Well, it’s just my suggestion as well; I think the suggestion from above is quite reasonable, for your reference!
The adjustment precision differs, and the CV of the V-ball is higher; perhaps the opening angle is not as good as that of a globe
A globe is better. Why think of switching to a V-shaped ball? Besides, it’s still a gas
The curve of V-ball can only achieve something similar to true equal percentage, but not actual equal percentage. Whether it can serve as a substitute needs to be determined on a case-by-case basis, depending on your operating conditions and requirements for adjustment
V-ball is cheaper; I want to try it out to see if it works
It has no impact; it mainly depends on how linear the control valve is – there is only a slight difference in flow rate at corresponding opening degrees.