2 replies to this topic

[rsk]

how the selection & sizing of control valve differs in
1.water flow from a tank & piping downstream
2.steam flow from a boiler
Also please how the rangebility of CV has bearing on energy saving.

[Zauberberg]

It depends on the overall system layout. And particular service which is in question here. And control scheme is very important as well.

The question is too general, and we can only speculate what is behind. Please make some effort in providing full system description, and we will be able to give you a useful answer.

Best regards,

[rsk]

Flow of liquids through piping transfer lines is generally controlled by the use of throttling valves. Past design practice has been to design the control valve to take from 25% to 50% of the system pressure drop. This gives the control valve a rangeability of approximately 50 to 1. The valve has converted work energy derived from electricity into frictional heat. Most processes don't require this much rangeability so a larger control valve with less pressure drop could replace the original valve, the rangeability being reduced say to ll to 1. Of course, energy savings can only occur if the pressure in the line is reduced, possibly by reducing the diameter of the pump impeller. The electric motor should also be replaced with one of lower horsepower that meets power requirements. Just installing a new control valve will be useless as the valve will throttle down until flow is controlled to the original point. Shinskey, in the "Control Systems Can Save Energy" article graphically discusses this energy saving idea.

From above how the larger valve reduces the rangeblity...