Manufacturing process of the valve body

There are valve bodies that are cast and those that are forged; casting is used for valves of larger sizes, while forging offers higher efficiency and better quality. Due to certain limitations, it is generally used for valves of smaller sizes.

I’m not sure what material you’ll choose; generally it’s cast, but it can also be made from forged parts.

Whether the valve body is manufactured using casting or forging methods depends on: 1. the nominal diameter size； 2. Pressure rating level ； 3. Material properties of the valve body ； 4. Medium temperature level ； 5. Factors such as the technological level of the manufacturing unit. As LZ mentioned, the valve bodies for PN6.4 and PN50 gate valves can be manufactured using the forging process.

The explanation on the 2nd floor is very thorough; modern manufacturing technologies are developing rapidly, and the overlap between forging and casting is increasing

It mainly comes down to cost and design format – whether it is a butt-welded or flanged type. For butt-welded or socket-welded valves, forging can be used, and this method improves the performance of the valve. However, for flanged valves, the forging cost is relatively high, making the overall forged design less economical

These days, vacuum casting or investment casting are generally used; forging might result in a lower cost for pipes with a diameter of 50

For DN50 and above, cast versions are generally used for this pressure rating

Forging offers better performance, but the processing method still needs to be chosen based on the specific structure and material.

Selection of the structural type of control valves 1.1 Issues to consider when selecting a valve based on its functional requirements 1) Control function ① The valve is required to operate smoothly； ②Good performance at low opening degrees ； ③Select the desired flow characteristics ； ④Meet the adjustable ratio requirement ； ⑤Low resistance and high flow ratio (the ratio of the valve’s rated flow parameter to its nominal diameter) ； ⑥Adjust the speed. 2) Leakage rate and shut-off pressure difference: These are two interrelated and inseparable factors. The leakage rate must meet the process requirements, and there must be protective measures to ensure the reliability of the sealing surfaces ； The cut-off pressure difference (the pressure difference when the valve is closed) must be specified (regrettably, this parameter is not included in the calculation specifications for control valves provided by many design firms); otherwise, the selected valve will not have sufficient output force to overcome it, which could result in an actuator that is either too large or too small. 3) Clogging prevention: Even with clean media, clogging can still occur. This happens when impurities in the pipeline are carried into the control valve by the medium, resulting in blockages. This is a common fault, so the clogging prevention capabilities of the valve should be taken into consideration. Generally, angle-type control valves have much better anti-clogging performance than straight-stroke type control valves; therefore, the use of angle-type control valves will increase in the future. 4) Corrosion resistance: It includes erosion resistance, cavitation resistance, and corrosion resistance. It mainly relates to the selection of materials and the service life of valves, as well as economic considerations. The essence of this issue is that the selected valve should have good corrosion resistance and a reasonable price. If full perfluoroelastomer valves are an option, then full corrosion-resistant alloy valves should not be chosen ； If an angular high-pressure valve with better anti-cavitation performance and a simpler structure (providing a service life of around two years) is available, then other high-pressure valves with more complex structures and higher costs should not be chosen. 5) Pressure and temperature resistance: This involves the selection of the nominal pressure and operating temperature of the control valve. In terms of pressure resistance, it’s not difficult to handle high pressure per se; the main issue is that large pressure differences can cause cavitation ； In terms of heat resistance, it is usually very easy to handle temperatures below 450°C, and temperatures between 450°C and 600°C are not difficult either; however, above 600°C, problems become more apparent ； When the temperature is 80°C, it is generally not advisable to use soft-sealing materials for cut-off control valves; hard-sealing cut-offs should be considered instead. The relationship between the operating temperature, operating pressure, and nominal pressure for commonly used materials is shown in Table 5-1 below. 6) Weight and appearance: This issue is quite straightforward – valves with a good appearance and low weight are the ones favored by manufacturers. Here, a prejudice needs to be changed: the idea that control valves are something crude and simple, that a heavier weight or a less attractive appearance means they are not special in any way. We now attach great importance to it, which has led us to propose that control valves should feature compactness, light weight, and instrumentation.

Working temperature, working pressure, and relationship with PN for commonly used materials
Material Nominal pressure PN (Mpa) Medium Working temperature (°C)
＜120 ＜200 ＜250 ＜300 ＜350 ＜400 ＜425 ＜450 ＜475 ＜500 ＜525 ＜550 ＜575 ＜600 ＜625

Maximum working pressure (MPa)
Cast iron: 1.6 1.6 1.5 1.4 – – – – – – – – – – – –
Carbon steel: 4.0 4.0 4.0 3.7 3.3 3.0 2.8 2.3 1.8 – – – – – – – 6.4 6.4 6.4 5.9 5.2 4.7 4.1 3.7 2.9 – – – – – – – 22.0 22.0 22.0 20.2 18.0 16.1 14.1 12.7 9.8 – – – – – – – 32.0 32.0 32.0 29.4 26.2 23.4 20.5 18.5 14.4 – – – – – – –
1Crl8Ni9Ti: 4.0 4.0 4.0 4.0 4.0 4.0 3.0 2.7 2.4 2.1 1.9 1.7 1.4 1.1 0.8 0.5 6.4 6.4 6.4 6.4 6.4 6.4 4.4 4.2 4.0 3.8 3.5 3.4 3.2 2.9 2.6 2.2 22.0 22.0 22.0 22.0 22.0 22.0 16.5 14.8 13.2 11.5 10.5 9.3 7.7 6.0 4.4 2.7 32.0 32.0 32.0 32.0 32.0 32.0 24.0 21.6 19.2 16.8 15.2 13.6 11.2 8.8 6.4 4.0
Molybdenum steel and chrome-molybdenum steel with at least 0.4% molybdenum: 4.0 – – – – 4.0 3.6 3.4 3.2 2.8 2.2 1.6 – – – – 6.4 – – – – 6.4 5.8 5.5 5.2 4.5 3.5 2.5 – – – – 22.0 – – – – 22.0 20.1 19.0 17.9 15.7 12.2 9.0 – – – – 32.0 – – – – 32.0 29.1 27.5 25.9 22.7 17.6 13.0 - - - -

Generally speaking, forging offers better performance, especially for large-sized items. Using forging results in much higher costs, but it has advantages when producing small batches – it’s possible to produce one or two units without having to do it in bulk； If flanges are present, overall forging will certainly result in high costs; the flanges can also be welded on separately, which helps to reduce costs