Gate Valve Bonnet

There are three main types of valve bonnets. The screwed-in bonnet is the cheapest type. It is also the least reliable, because tight sealing of the stem 

The use of a rack-and-pinion-operated valve or worm-gear-operated valve instead of lever is suggested for valve operation in propane service if the valve is 3 inches or larger or for any service in which there is a substantial pressure differential across the valve in the closed position. 

The first ductile-iron -valves did not comply with API standard 600 but did meet ANSI B16.5. Many petro-chemical plants and refiners are now interchanging ductile-iron valves with steel valves with a temperature service limit of 600° F. 

The industry has agreed to an 80% rating on ductile-iron valves based on a Navy evaluation. Ductile-iron valves are good for 80% of the ANSI rating only. These valves are generally made only in 150-pound series at the present time. Therefore, ductile-iron valves could be applied only to 120-pound service or lower. One big advantage noted for ductile iron valves is that prices are about 80% of those for steel valves. 

Some refiners are still concerned about the safety hazard of ductile-iron valves. They feel that during a fire there is a possibility that the valve would break like cast iron when cold water is poured on it. Another problem is in being sure of actually receiving ductile iron when it is specified. The only solution at present is to pick a reliable supplier. 

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Gate valves are used to minimize pressure drop in the open position and to stop the flow of fluid rather than to regulate it. The problem, when the valve is closed, of pressure buildup in the bonnet from cold liquids expanding or chemical action between fluid and bonnet should be solved oy a relief valve or by notching the upstream seat ring. 

Bolted Bonnet Steel Gate Valves for Petroleum and Natural Gas Industries... 

Globe valves are used in HCN service. Gate valves should not be used since they can trap HCN in the bonnet cavity, which can polymerize violently254. 

These 600-pound steel gate valves in 1/2-inch and 3/4-inch sizes have hard-faced or 13-chrome seats with a hardness of 250 to 500 Brinell. Most of them have a 13-chrome wedge and a bolted bonnet although welded and union bonnets are available. Spiral-wound or soft-iron gaskets are used. 

The term trim applied to gate valves generally refers to material from which the stem, disc faces and seats are made. Certain other parts such as inside screw-wedge bushings, bonnet bushings, yoke-stem nuts and yoke-wheel-clamp nuts may be made of trim material. 

Gate and Globe Valve Bolted Bonnet and gland Bolted Bonnet and gland Bolted Bonnet and gland Bolted Bonnet and gland - -... 

VALVES. Various valve styles may be used including globe, gate and ball. A vent connection is provided at the bonnet flange to permit the installation of a safety device and/or a purge valve. When the valve is closed, this connection communicates only with the piping downstream of the valve,... 

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