Question 1

What is a ball valve and how does it work?

Accepted Answer

A ball valve is a quarter-turn shutoff device that uses a spherical ball with a bore through its center. The ball rotates inside a body between two seats. When the bore aligns with the pipe, flow passes through; when the handle or actuator turns the ball 90 degrees, the solid part of the ball blocks the flow path. Because the ball surface contacts the seats continuously, ball valves provide bubble-tight shutoff and are best suited for on/off service, although V-port or characterized balls can be used for throttling in certain applications.

Question 2

What is the difference between a floating ball valve and a trunnion ball valve?

Accepted Answer

In a floating ball valve the ball is supported only by the two seats and moves slightly downstream under pressure; this design suits smaller sizes and lower pressures, usually up to 6 inches and Class 600. In a trunnion ball valve the ball is supported at top and bottom by bearing trunnions, stays centered under high pressure and the seats are spring-loaded against the ball; trunnion designs are used for larger sizes and higher pressures, from 6 inches up to 60 inches and Class 1500 or Class 2500, and often provide double block and bleed capability.

Question 3

What materials are available?

Accepted Answer

Body materials include carbon steel WCB and LCB, stainless steel 304, 316, 316L and 321, duplex 2205, super duplex 2507, alloy 20, Monel, Inconel, brass, bronze, and plastics such as PVC, CPVC and PVDF. Seat materials include PTFE, RPTFE, PEEK, nylon, Delrin, metal seated, graphite, EPDM and FPM. For severe service, tungsten carbide coatings, hard chrome plating and Stellite overlays can be supplied on balls and seats.

Question 4

How do I choose the right size and pressure rating for a ball valve?

Accepted Answer

Start with pipe size and flow requirements: full bore valves match the pipe inside diameter and minimize pressure loss, while reduced bore valves are smaller and more economical. Then calculate maximum operating pressure and temperature and compare against pressure-temperature ratings in ASME B16.34 or the relevant standard, selecting a class with margin, typically at least 25% above maximum working pressure. Also confirm connection type, end standard and whether the service is corrosive or abrasive.

Question 5

Can ball valve be used for throttling or flow control?

Accepted Answer

Standard ball valves are designed for on/off service because partial opening can cause high-velocity flow that erodes seats and ball. Special V-port or characterized ball valves with a V-shaped notch or contoured bore provide a more linear flow characteristic and are used for throttling in chemical dosing, steam control and gas flow regulation. For most shutoff applications a standard full bore or reduced bore ball valve is the correct choice.

Question 6

What is the difference between full bore and reduced bore?

Accepted Answer

A full bore ball valve has a ball opening approximately the same inside diameter as the connecting pipe, so there is no flow restriction; these are used where pigging, slurry service or minimal pressure drop is required. A reduced bore ball valve has a ball opening one pipe size smaller than the nominal pipe size, for example a 2-inch reduced bore valve may have a 1.5-inch ball opening. Reduced bore valves are lighter, smaller and less expensive and suit most general on/off services where slight pressure drop is acceptable.

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