Home technical BACK TO BASIC: BALL VALVES

BACK TO BASIC: BALL VALVES

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INTRODUCTION

A ball valve is a device used in pipelines to open and shut off the fluid flow. They are used in smaller bore pipelines, to operate them manually. Large size ball valves are motor-operated. They are quarter-turn valves. They are easy and quick to operate as compared to gate and globe valves.  Multi-turn valves take slightly more time to open and close the fluid flow. Plug and butterfly valves are also in the category of quarter-turn valves. Ball valves are mainly used for liquids containing slurry particles under suspension. Ball valves are available in two and three-piece construction. Their advantages are discussed here.

THREE-PIECE BALL VALVE

The forged steel ball valve has three main components, Body, Ball, Body connectors. Other parts are indicated in the exploded view of the three-piece valve

Exploded view of the three-piece ball valve.

MATERIAL OF CONSTRUCTION OF BALL VALVE:

(1) LEVER——– Carbon Steel
(2) Lever nut—- Carbon Steel
(3) Nameplate—- Aluminium
(4) Washer spring– Harmonic Steel
(5) Gland packing— Inox
(6) Packing——— PTFE + 25% Glass- Grafoil
(7) Stem-o-ring—– Viton
(8) Stem————- Cr 13
(9) Seats———— PTFE+ 15% Glass
(10) Ball———— Cr 13
(11) Body Gaskets—– PTFE+ 15% Glass
(12) Fire-safe Gasket–Grafoil
(13) Bolts————-A193 B7
(14) End connectors— A105
(15) Body————–A105

BALL VALVE TWO-PIECE CONSTRUCTION:

The ball valve has three main components, Body, Ball, Body connectors. Other parts are indicated in the exploded view of the two-piece valve.

Exploded view of the two-piece ball valve.

ADVANTAGE OF BALL VALVE:

Quarter turn ball valves have some advantages over the multi-turn gate and globe valves.

(1) In the ball valve, the valve stem rotates in the valve packing, while in the gate and globe valves the valve stem slides up and down in the valve packing. This sliding movement of the stem through valve packing may cause fluid leakage into the atmosphere through the valve stem, which is not permissible in case of hazardous and precious fluid.

(2) The size and weight of the quarter-turn valve are less than the multi-turn gate and globe valve. When size and weight are the concern for the installation of the valve, then a quarter-turn valve is the best choice.

(3)Quarter turn valve has a quick movement of ball hence quick open and close of fluid flow as compared to the multi-turn valve.

BALL VALVE SELECTION:

The selection of a proper ball valve is a matter of great concern. Usually, the ball valves are prone to leakage through stem packing and body packing. Particularly in small bore ball valves, extended nipples to be used. While welding these valves, between the piping’s, welding heat will not travel up to body packing and they are saved from damage. This precaution reduces ball valve failure. Thus the plant uptime is increased and the maintenance cost is reduced. To get a correct valve selection for our service from the manufacturer, the subsequent information to be provided to the valve manufacturer. This information must include the following information:

(1)Pipe size, schedule, and material.

(2) Design Pressure.

(3) Design temperature.

(4) Valve upstream operating pressure.

(5) Valve upstream operating temperature.

(6) The flow rate of the fluid.

(7) The allowable pressure drop across the valve.

(8) Fluid flowing through the valve.

(9)Ball Valve end connections are constructed in, Socket weld, Bevel weld, and flange.

(10)The material of construction of Body, Trim, Bonnet bolt, bonnet nut, seat to be specified.

(11)Bonnet Type(welded or bolted).

(12 stems and body packing material.

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