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Question:

Why use steel over brass in valve spindles?

HowdyWas taking apart a screw down NR valve and screw lift valve and noticed the spindles were made out of different materials. Brass and Steel.I am aware that brass is non corrosive but why use steel in the other valve? Is it due to their operation, do they come or not come in contact with fluids? Is one cheaper than the other?The screw lift globe valve had a steel spindle and the screw down nr glove valve had a brass spindle.Also, if anyone knows what materials are used in the valve lid and seat are made of.Any ideas?Cheers

Answer:

Brass is used in some cases because it it less likely to corrode. It is used in other cases because it is softer than steel and can act as a bearing surface. Steel is usually used because of its strength relative to brass. In some cases they are used in combination so the steel surface and the brass surfaces compliment each other to provide a smooth sliding surface. Bronze is also a popular material for some valves and parts of other valves. Usually in water or steam service. Many times the valve seats are made from a harder material such as stellite. See site below for more info on stellite.
*In steam service , steam flashing is one of the factor which erode the spindle ( say valve stem) *The stem serves as a connector from the actuator to the inside of the valve and transmits this actuation force. Stems are either smooth for actuator controlled valves or threaded for manual valves. The smooth stems are surrounded by packing material to prevent leaking material from the valve. This packing is a wearable material and will have to be replaced during maintenance. With a smooth stem the ends are threaded to allow connection to the plug and the actuator. The stem must not only withstand a large amount of compression force during valve closure, but also have high tensile strength during valve opening. In addition, the stem must be very straight, or have low run out, in order to ensure good valve closure. This minimum run out also minimizes wear of the packing contained in the bonnet, which provides the seal against leakage. The stem may be provided with a shroud over the packing nut to prevent foreign bodies entering the packing material, which would accelerate wear. Disc material: Cast Iron or Ductile Iron Disc Aluminum-bronze Disc Stainless Steel Disc Nickel-plated Ductile Iron Lid material: engineering plastics, Cast Iron. Seat material[hard/soft]: Seats can be integral to the valve body, that is hard metal or plastic. *Hard seat: Hardened steel,Cast Iron,EN-52 forging steel Valve Seats are made from Chrome Alloy Steel which has a high wear resistance at high temperature. Nearly all metal seated valves leak, even though some leaks are extremely small. *Soft seats can be fitted to the valve body and made of materials such as PTFE or various elastomers such as NBR, EPDM, FKM. Each of these soft materials is limited by temperature (rough maximum temperatures are listed below) NBR 80 °C EPDM 120 °C FKM 170 °C PTFE 200 °C

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