A ductile iron ball valve has a body and end connections made of ductile iron, which has better strength and durability than standard cast iron. The spherical disc is also typically ductile iron.
Advantages include high strength, corrosion resistance, good flow characteristics, and the ability to withstand high pressures and temperatures. Ductile iron is less brittle than cast iron.
ypical uses are for on/off and throttling control in water, wastewater, steam, chemical, petroleum, and other general industrial applications. Common examples are district heating plants and mining slurry pipelines.
The main components are the body, ball, stem, seat rings, gland follower, packing, and end connections. The bolt attached ball allows tight shutoff.
Rotating the handle 90 degrees turns the ball with the bore perpendicular to the seats, blocking flow. Rotating it back aligns the bore with the seats, allowing flow through the valve.
Size is based on the pipe diameter, required flow rate, and pressure rating. Oversizing the valve can cause flow control problems.
Common end connections are flanged, threaded, welded, grooved, and specialty connections like hub, mechanical joint, or wafer.
Most have a rising stem that lifts the ball off the seat during opening. Some have non-rising stems with stop collars instead. Stems are typically stainless steel or chrome plated.
Maintenance involves cycling the valve, lubricating threads, and replacing seals and gaskets. Repairs require valve disassembly to access internal parts. Lapping the ball and seats can refurbish shutoff.
Key standards include MSS SP-72, ANSI/AWWA C507, API 6D, ISO 17292, and API 608. Ductile iron ASTM grades are important for material strength.
Maximum pressures range to 740 psi or higher. Temperatures can range from -30°F to 450°F or up to 750°F with special internals. Check manufacturer specifications.
Corrosion resistant coatings, using stainless steel balls and stems, and cathodic protection are used. Regular cycling, draining, and general maintenance also reduce corrosion.