non-pressure compensated flow control valves

NON-PRESSURE COMPENSATED FLOW CONTROL VALVES

1. What are Non-Pressure Compensated Flow Control Valves?

• The non-pressure compensated type flow control valves are used where system pressures vary considerably and precise flow-rate controls are not required.

• These valves operate based on the principle that the flow through an orifice will be constant, if the pressure drop remains constant.

• All the simple valves such as globe, needle, butterfly, gate, and ball valves are non- pressure compensated valves.

2. Globe Valve

In a globe valve, flow rate can be changed by means of a disk, plug, or ball which nests against a seat, as shown in Fig.6.20, 6.21, and 6.22 respectively.

1. Disk-type globe valve : Disk-type globe valve, also known as a butterfly valve, consists of a large disc which is rotated inside the pipe, the angle determining the flow rate, as shown in Fig.6.20.

2. Plug-type globe valve: Plug-type globe valve has a tapered plug that can control the flow rate by varying the vertical plug position, as shown in Fig.6.21.

3. Ball-type globe valve : Ball-type globe valve has a ball with a through-hole which is rotated inside a machined seat, as shown in Fig.6.22.

3. Needle Valve

• The needle valve has a pointed stem that can be adjusted manually to control the flow rate of fluid through the valve, as shown in Fig.6.23.

• Needle valves have a smaller flow area and higher pressure drop than the globe valve.

4. Applications of Non-Pressure Compensated Flow Control Valves

1. The globe valves are used to throttle only in lines where the liquid velocity is relatively low.

2. In comparison to globe valves, needle valves are more suitable in throttling the flow for any velocity.

5. Limitations of Non-Pressure Compensated Flow Control Valves

In both globe and needle valves, changes in the pressure drop produce variations in the flow rate. Therefore precise accuracy in flow-rate control and hence the speed control cannot be achieved by using non-pressure compensated flow control valves.