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ベランスベローズ型安全弁
ベランスベローズ型安全弁は、従来のスプリング式リリーフ弁の定格が背圧で低下する条件でも設定圧力を安定させます。ベローズがばねとディスクガイドを放出側から分離し、時間的に変動する重畳背圧を打ち消します。サイズ、クラス、設定圧力範囲、ボディ・ベローズ材はRFQ時に必要容量と背圧条件に対して確認します。背圧下でも容量は低下します。API 520のKb係数はおよそ30～40%の背圧から低下し、そのチャートは選定を50%で打ち切り、API 526は38℃超で許容限界をさらに下げ、ベローズ自体の容積はKw/Kb補正でノズル面積を食います。ベローズは消耗品（推定故障率2～6%）で、破断は不安定な開弁と漏れとして現れるため、ボンネットのセンチネルベントは開放し安全な場所へ配管します。サワーサービスではNACE MR0175に基づくNi-Cr合金625ベローズが必要です。選定は背圧の変動、Kb適用後の必要容量に対するオリフィス面積、媒体に対するボディ・ベローズ材、実用最小設定圧約1bargがポイントです。
次のファミリーに属する： 安全弁 ファミリー
最終更新： 2026-11
ファミリー仕様
| bellows definition function | Bellows isolates the area above the disc from superimposed back pressure so set pressure does not shift with header pressure, and additionally prevents corrosion between the disc holder and guide (Crosby PRV Engineering Handbook definition) |
|---|---|
| kb chart window 30 50pct | API 520 Kb chart for balanced bellows valves: the Kb factor starts to decrease when backpressure exceeds roughly 30-40% of set pressure (depending on overpressure), and the chart is limited to 50% backpressure as the maximum selection limit |
| kb undersizing risk | Ignoring the backpressure correction factor undersizes the valve: with an actual Kb of 0.80, assuming Kb = 1.0 yields a required orifice area about 20% smaller than actually needed, risking vessel overpressure |
| backpressure performance degradation 30pct | Field reference: balanced bellows flow performance starts degrading at back pressures above roughly 30% of set point, and the bellows has mechanical-integrity limits at high header pressure on large valves |
| api526 backpressure limit temperature | Per API Std 526 the allowable backpressure limit for balanced safety valves is generally lower than for conventional designs because of the bellows; above 38 C (100 F) operating temperature the allowable limits may decrease further, so the manufacturer should be consulted for higher-temperature or higher-backpressure duty |
| capacity derating kw kb | Because the bellows occupies internal valve space, balanced bellows valves under backpressure show reduced flow capacity and higher fluid velocity; Kw (liquid) and Kb (gas) correction factors apply and the required nozzle area is usually larger than for valves without backpressure or bellows |
| bellows material sour service | In highly corrosive service such as hydrogen sulfide environments the bellows must be nickel-chromium alloy 625 per NACE MR0175 requirements (page lists SS316L standard / nickel-chromium alloy high-temperature; sour duty requires the NACE-grade alloy) |
| bonnet vent sentinel hole | Every balanced bellows safety valve must have an open bonnet vent hole: it keeps bonnet internal pressure at atmospheric so pressure cannot act on an area larger than the nozzle sealing area, and doubles as the sentinel hole used to monitor bellows integrity; in corrosive, toxic or flammable service the vent must be piped to a safe location |
| bellows rupture consequences | A ruptured bellows loses the balancing function: backpressure influence increases sharply, process media enter unintended areas causing leakage and internal bonnet corrosion, and the valve may show unstable opening or abnormal reseating until shutdown, repair and retest |
| bellows failure rate balanced diaphragm | Bellows failure rate is estimated between 2% and 6%; OEM balanced-diaphragm executions replace the bellows and extend backpressure limits from 60% to 80% while raising the Kb factor by up to 15%, and tolerate rapid cycling better than bellows |
| bellows leak detection ldar gap | Bellows ruptures are hard to detect and may go unnoticed for years until periodic service: LDAR programs target flanges and valve seats, so fugitive emissions through the bonnet vent can fall outside LDAR scope; OEM bellows-leak-detection (backup piston + pressure transmitter) gives immediate notification |
| minimum set pressure limit | The bellows spring rate limits low set pressures: minimum set pressure of balanced safety valves is usually higher than conventional valves, typically around 1 barg (15 psig) |
| large orifice bellows recommendation | For large nozzle series (Q, R, T) with set pressure below 3.0 barg (43.5 psig), bellows construction is recommended even without variable backpressure, because the bellows smooths disc reseating during discharge |
| chatter backpressure instability | Fluctuating backpressure can cause valve chatter or oscillation that eventually damages the seat; even with balanced bellows construction, poor reseating can persist if the valve is oversized, guides are contaminated, or the seat is already chatter-damaged |
| bba orifice diameter series | Actual Orifice diameter d 0 [mm] 18 18 23 29 37 46 60 74 92 98 125 165 |
| bba orifice area series | Actual Orifice area A 0 [mm2] 254 254 416 661 1075 1662 2827 4301 6648 7543 12272 21382 |
| bba weight with bellows | with bellows 9,4 9,4 10 13 17 24 36 60 83 93 142 289 |
| bba standard bellows min set pressure | 3 3 3 3 3 3 3 2.74 2.01 0.2 standard bellows |
| bba low pressure bellows min set pressure | 2.00 0.98 1.41 1.11 1.81 1.50 1.05 1.18 1.41 low press. bellows |
| bba ansi valve size series | 1" x 2" 1" x 2" 1" x 2" 2" x 3" 3" x 4" 4" x 6" |
| bba ansi flange class | Inlet CL150 or CL300 Class1) Outlet CL150 |
| bba xxl size series | DN I+O 200 x 300 250 x 350 300 x 400 400 x 500 |
| bba xxl orifice area | Actual Orifice area A 0 [mm2] 21382 31416 43374 68349 |
| bba xxl seat materials | Seat DN 200 250 1.0305 stellited 1.4571 Carbon steel, stellited 316Ti DN 300 400 1.0460 stellited 1.4571 Carbon steel, stellited 316Ti |
| bba ansi trim materials | 1 Body 1.0619 1.4408 SA 216 WCB SA 351 CF8M 5 Seat 1.4404 1.4404 316L 316L 7 Disc 1.4122 1.4404 Hardened stainless steel 316L |
| bba gasket materials | Graphite / 1.4401 Graphite / 1.4401 Graphite / 1.4401 Graphite / 1.4401 Graphite / 316 Graphite / 316 Graphite / 316 Graphite / 316 |
| bba bellows height adder | Bellows H max. 378 497 534 602 741 902 |
| bbb bellows area balance | the effective area of the bellows is equal to or greater than the sealing area of the disc and nozzle |
| bbb asme xiii opening tolerance | the valve will open at the same value obtained on the test bench (within the tolerance allowed by the ASME Code – Section XIII – in Table 3.6.3.1- 2 – 2023 Edition) |
| bbb variable backpressure requirement | the user must specify a balanced pressure relief valve with bellows |
| bbb conventional builtup backpressure limit | the limit of this type of backpressure is 10% of the valve set pressure for an overpressure also of 10% |
| bbb isolation function jamming media | To avoid these situations, it is recommended to specify balanced valves with bellows, with the bellows having an isolation function. |
| bbb cdtp not required dirty service | there is no need for cold differential adjustment (CDTP) to compensate for the effect of the backpressure on the valve set pressure value, as is mandatory for a conventional valve. |
| bbb upper component material economy | components above the bellows, such as the bonnet, stem, spring, spring supports, spring adjustment screw, adjustment screw lock nut and cap, to be constructed of materials that are less resistant to corrosion |
| bbb outlet rupture disc protection | it is also recommended to specify a balanced bellows valve |
| bbb elastic constant min set pressure | the elastic constant of the bellows prevents a lower set pressure |
| bbc kb factor scope | Kb = Backpressure correction factor, for balanced bellows valves only (otherwise, use 1.0) |
| bbc unbalanced set pressure shift | a relief valve set at 150 psig with 43 psig superimposed backpressure will lift at 193 psig |
| bbc conventional lift profile | Typical conventional style balanced or unbalanced SRV's crack at approximately 90% of set (simmer) then advance to full lift at 100% of set (10% overpressure). |
| bbc bellows execution prevalence | Most balanced pressure relief valves use bellows. These are expensive to purchase and maintain. |
範囲と出所の注記
| back pressure capability wording | Back-pressure capability wording: API 520 Kb chart and API 526 limit the balanced-bellows selection window (Kb decay from ~30-40%, chart cap 50%, temperature derating above 38 C), while field references note flow degradation starting near 30% of set point; page states no single back-pressure percentage, correction factors and per-manufacturer limits govern selection. |
|---|---|
| minimum set pressure tension | Minimum set pressure tension: catalog range lists 0.1 MPa set pressure lower bound, but the bellows spring rate typically raises the practical minimum to around 1 barg; below that, constructions should be confirmed with the manufacturer. |
注文と書類
書類
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よくある質問
ベランスベローズ型安全弁の見積依頼には何を含めるべきですか？
適用規格とクラス、呼びサイズ、ボディおよびシート材、使用媒体と温度、納入先——欠落している項目は見積の過程で確認します。
ベランスベローズ型安全弁にはどのサイズと圧力等級がありますか？
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ベランスベローズ型安全弁にはどのボディ材質がありますか？
このバルブの検証済みボディ材質範囲はまだ本ページに掲載されていません——お客様の使用条件に適したボディ材質は見積の過程でご提案し、確認します。使用条件を問い合わせに添えていただければ、選定結果を見積書に記載します。
ベランスベローズ型安全弁 の見積依頼
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