Question

7 Unlike a ball valve, the disc is always present within the flow; therefore a pressure drop is always induced in the flow, regardless of valve position. How is this possible? Explain. (2 marks; each 1 mark). Butterfly valve is also used to incrementally regulate flow in the oil industry sector. What is the guarantee for this? Explain. (2 marks; each 1 mark). With the butterfly valve's sealing ability and its resistance to wear, the valve is best suited for high pressure systems in the oil & gas industry operations. How do you say this? Explain (1 mark: each 0.5 mark)

Answer 1

he disc is the part which allows, throttles, or stops flow, depending on its position. In the case of a plug or a ball valve, the disc is called plug or a ball. The disk is the third most important primary pressure boundary. With the valve closed, full system pressure is applied across the disk, and for this reason, the disk is a pressure related component.

Disks are usually forged, and in some designs, hard surfaced to provide good wear properties. Most valves are named, the design of their disks.

Rotating the actuator turns the disc either parallel or perpendicular to the flow therefore a pressure drop is always induced in the flow, regardless of valve position.

quarter-turn rotational motion valve, the butterfly valves is used to stop, start and regulate flow. Easy and fast to open, the valve usually comes equipt with a gearbox where the hand wheel by gear is connected to they stem.

This simplifies the operation of the valve, but at the expense of speed. These valves must also be installed a minimum of 6 pipe diameters away from other line elements.

As well as being lightweight, and quick to use, the butterfly valves are available in large sizes and can cope with low-pressure drop and high-pressure recovery.The pressure loss through a butterfly valve is small in comparison with the gate valve. The L/D ratio for this type of valve is approximately one-third of that of a gate valve.

The high-performance double offset butterfly valve, used in slightly higher-pressure systems, is offset from the centre line of the disc seat and body seal (offset one), and the centre line of the bore (offset two). This creates a cam action during operation to lift the seat out of the seal resulting in less friction than is created in the zero offset design and decreases its tendency to wear. The valve best suited for high-pressure systems is the triple offset butterfly valve. In this valve the disc seat contact axis is offset, which acts to virtually eliminate sliding contact between disc and seat. In the case of triple offset valves the seat is made of metal so that it can be machined such as to achieve a bubble tight shut-off when in contact with the disc.