Bürkert explains the importance of sizing control valves correctly

Making the correct control valve selection is largely based on a combination of theoretical calculations. Some quick arithmetic can be the difference between an efficient flow control application or costly failure. Process Industry Forum spoke to fluid control experts Bürkert about common valve selection criteria and how their fluid velocity calculator can make sizing the right control valve a breeze.

Control valve selection criteria

There are three main valve selection criteria to weigh up when choosing the correct type and size of valve for your application. Ascertaining these factors will make your control valve selection process infinitely easier and more accurate. These quick calculations can be the difference between an efficient, reliable and cost-effective valve installation and one that quickly fails.

One consideration is the Kv factor, a standardised figure for the achievable flow rate of a fluid through a valve. Another factor to bear in mind is flow rate, which determines how much volume of fluid flows through a valve at any given time. Finally, there’s pressure drop; the difference between the input pressure of the medium upstream of the valve and the back pressure downstream of the valve.

What happens when you make the wrong control valve selection?

Valves are incredibly important components in many process systems, which makes it essential to select the right sized valve for the application. Failure to do so can cause damage, such as control valve cavitation and flashing, and jeopardise the integrity of your fluid system. This can eventually end up costing you precious time and money in downtime, repairs and replacements.

If a control valve is undersized, even if it is fully opened it is highly unlikely to deliver the desired flow rate. When higher pressures are applied to such a valve in order to force a higher flow rate two things may occur: excessive pump energy and flashing or cavitation damage to the valve.

Flashing occurs when liquid flows through a control valve, vaporises and remains a vapour. This can limit flow through the control valve and the liquid-vapour mixture can cause erosion that is smooth and shiny in appearance. Cavitation happens as a result of imploding vapour bubbles, which create pitting in the metal surfaces of valves and pipes. Not only does cavitation reduce flow efficiency but it can also cause excessive vibration and noise.

If the selected control valve is too large, on the other hand, it will be impossible to attain the required control for the application. When a valve operates below its Kv for an extended period of time, there is a high probability that the valve seat will become damaged. As the most critical component of a valve, if the seat fails the valve simply will not work. The consequences of which can range from minor leakage to catastrophic failure.

Bürkert’s free fluid velocity calculator

As you can see, sizing a control valve properly is critical to the effectiveness of any flow control application. Thankfully, Bürkert can remove all the guesswork and help you to calculate the flow factor, flow rate and pressure drop of a valve using their free online fluid velocity calculator. With the Bürkert fluid velocity calculator, you can make an informed control valve selection; saving considerable time, expense and frustration in the process!

For more information, please contact Bürkert today.