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先導式安全閥
先導式安全閥將主閥與外部先導閥配對：先導閥感測管線壓力並控制主閥，在整定壓力下全開、啟閉壓差短，且在整定壓力以下保持動態密封——因此操作壓力可以貼近整定壓力運行而不產生前洩或介質損失。典型壓力覆蓋為 DN25-DN200（1" x 2" 至 8" x 10" 入口 x 出口），ANSI Class 150-600 / PN16-PN100，閥體 WCB、CF8 或 CF8M；整定壓力窗口在報價時依所需排量與先導閥選型確認。先導閥有突開式（pop-action）與調節式且可現場選擇；調節式耐受更高的疊加背壓。法蘭（RF）端接。先導架構帶來性能餘量：由於活塞腔面積大於閥座面積，主閥在彈簧閥已前洩的壓力下仍保持密封至整定壓力的 5% 以內（98% 閥座密封度）；突開式先導閥在約 1% 超壓開啟、97% 回座（可調至 85%，啟閉壓差 -3% 至 -15%）；調節式先導閥跟隨需求並在 110% 整定壓力達全開；背壓至 70%——特殊情況 95%——可配防倒流器補償。主導失效模式是先導感知管線：含顆粒或結晶介質會堵塞其約 10 mm 孔口（保持閥門僅用於潔淨服務，注意結焦與聚合），快速啟動升壓可使活塞腔失衡造成假開啟。安裝保持遠程取壓在 100 英尺內、等效 3/8 吋面積，供應管線上不得設阻斷閥，現場測試接口支持在線功能測試。ASME VIII UG-126(b) 要求先導閥自力動作、主閥在全排量下失效開啟（fail-open）。選型取決於操作壓力對整定壓力之比、背壓、介質與先導閥動作型式。
屬於 安全閥 系列
最後更新： 2026-11
系列規格
| Pressure class / nominal rating designation | ANSI Class 150-600 / PN16-PN100 |
|---|---|
| Nominal valve connection size | DN25-DN200 (1in x 2in - 8in x 10in inlet x outlet) |
| Valve body material | WCB, CF8, CF8M |
| End connection types | flange (RF) |
| Service temperature range | -162 to 320°C |
| pilot type | pop-action or modulating; field-selectable |
| design note | main valve + external pilot; full-lift at set pressure with short blowdown |
| operating pressure ratio vs spring limit | Spring-loaded valves struggle to close completely above roughly 90% of set pressure; the pilot-operated main valve closes with a dome area larger than the seat area so closing force exceeds opening force, letting system operating pressure run within 5% of set pressure without increased seat leakage - the standard choice for high operating-to-set ratios |
| pop action reseat and adjustable blowdown | Pop-action pilot: opens at about 1% overpressure, closes at 97% of set pressure adjustable down to 85%, with blowdown adjustable between -3% and -15% above the API standard; modulated-closure pilots hold blowdown to max 7% |
| modulating vs pop pilot principle | Pop-action fully empties the main-valve dome for snap full lift; in modulate action the dome is only partially emptied, with the extent of emptying determined by the inlet pressure, so the main valve modulates with the relief demand |
| modulating partial opening capacity control | Modulating diaphragm-pilot execution: the valve opens further as process pressure rises and reaches full lift at 110% of set (High Gain option by 105%); the pilot is the nonflowing type - with the main valve relieving at steady pressure, no process fluid flows through the pilot |
| back pressure tolerance | Pilot actuation is differential, so back-pressure tolerance is high: pilot-operated safety valves can consistently compensate 70% back pressure and in certain cases run at a 95% back-pressure ratio; operability stays unaffected up to 70% of set pressure provided a backflow preventer is used whenever back pressure can exceed inlet pressure |
| seat tightness high operating ratio | Pilot-operated SRVs can achieve seat tightness up to 98% of set pressure for both the main valve and the pilot valve - the basis for running close to set pressure without simmer |
| posv definition | A pilot-operated safety relief valve is a pressure relief valve in which the major relieving device (main valve) is combined with and controlled by a self-actuated auxiliary pressure relief valve called a pilot valve |
| asme ug 126b pilot requirements | ASME Code Sec. VIII UG-126(b) permits pilot-operated pressure relief valves provided the pilot is self-actuated and the main valve opens automatically at not over set pressure and discharges full rated capacity even if some essential part of the pilot fails - the fail-open requirement |
| pilot blowdown short adjustment | The pilot portion of some pilot-operated valves can be set at blowdowns as short as 2% - far tighter than direct-spring pop valves |
| sensing line blockage failure mode | The pilot sensing (pressure-tap) line is the governing failure mode: media containing particles or prone to crystallization can plug the roughly ten-millimeter line, after which the safety valve can no longer perform its intended function; pilot-operated valves are supplied with filters and generally recommended for relatively clean service |
| dirty service limits | Pilot-operated valves should not be employed in abrasive or dirty service, where coking, polymerization or corrosion of wetted pilot parts can occur, or where the lading fluid can freeze or condense at ambient temperature; for severe dirty service where interconnecting tubing can clog, a pilot-operated SRV might not be the best fit |
| rapid pressure ramp false lift | During plant start-up with an extremely rapid system-pressure ramp rate, the dome area may not equalize with the same inlet pressure, resulting in insufficient closing force - a pilot-operated-specific false-lift mode |
| soft seal and temperature limits pilot | Pilot soft seals (O-rings) bound the application envelope: at temperatures of 200 °C and above the safety valve manufacturer should be consulted |
| sensing line remote pickup sizing rules | Installation rule for remote pressure pickup: piping must have the equivalent flow area of 3/8 in tubing for lengths up to 100 feet, longer runs require factory consultation; a block valve in the remote pilot supply line is not recommended and, if used, must be opened before pressurizing the main valve |
| field test connection in service | A field test connection allows operators to functionally test the pilot-operated SRV while it remains in service - a maintenance advantage over direct spring valves that must be pulled for bench testing |
| oem maintenance resources posv toolbox | OEM maintenance reference: the valve manufacturer publishes a dedicated maintenance toolbox for pilot-operated types 811 (pop action) and 821 (modulating) with repair guidance to the manufacturer quality standards |
| set pressure range example diaphragm pilot | OEM example envelope (pilot-operated relief valve with diaphragm pilot): set pressure range 15 psig to 740 psig; reseat pressure defined as the supply pressure where the dome pressure increases to 75% of supply pressure - an industry-reference anchor, not a tenant supply claim |
| Source 1 — orifice area range | effective orifice areas of 0.128 through 45.664 inches |
| Source 1 — inlet size range | valve inlet sizes 1-inch through 8-inch |
| Source 1 — Set-pressure range | set pressures from 15 to 3,705 psig (1 to 260 barg) |
| Source 1 — continuous temperature range | Continuous service temperatures from -50°F to +450°F |
| Source 1 — nonflowing pilot principle | with the non-flowing pilot provides highly reliable system overpressure protection |
| Source 1 — dirty service pilot design | The pilot is a non-flowing design minimizing the entry of dirt and the accumulation of hydrates |
| Source 1 — pilot supply filtration | Inline tubing external filter is also available |
| Source 1 — vertical pilot mounting | Consistent set pressure and blowdown are assured compared to horizontally mounted pilots that are erratic |
| Source 1 — orifice nozzle replacement | The orifice size may be changed by replacing a single component |
| Source 1 — external blowdown adjustment | Adjustable blowdown is external, reducing time and cost-consuming expenditures of valve removal |
| Source 1 — replaceable soft seat | With a replaceable soft seat, expensive parts and time-consuming lapping of metal seats are no longer necessary |
| Source 1 — asme capacity verification | capacity is assured by an independent third party, the ASME National Board Laboratory in Columbus, Ohio |
| Source 1 — operating ratio capability | The valve can be set within 5% of system operating pressure allowing the process to be maintained at close tolerance without valve leakage |
| Source 1 — typical applications | for Gas Compressors, Pressure Vessels, Cold Box Storage, Meter Runs, Gas Plants, Pipelines, and Transmission Stations |
| Source 2 — low pressure vacuum protection | provide safe, dependable, and accurate low pressure and/or vacuum protection |
| Source 2 — api2000 sealing | Seals in accordance with API 2000 requirements for Pilot Operated Relief Valves |
| Source 2 — rated flow overpressure | Rated flow at 10% overpressure provides the ability to operate closer to the tank MAWP, increasing the operating range of the process |
| Source 2 — seat action flexibility | Flexibility in terms of film or o-ring seat and snap or modulating action allows product customization to specific application requirements |
| Source 2 — vacuum breaker variant | The Model 1662A incorporates a vacuum breaker. |
| Source 2 — Nominal valve connection size | Sizes: 2” through 12” (50-300mm) |
| Source 2 — pressure settings | Pressure Settings: from 7.0* InWC to 15 psig |
| Source 2 — vacuum settings | Vacuum Settings: 7.0 InWC to 12 psig |
| Source 2 — standard body materials | Standard Body Materials: Carbon Steel (WCB/CS), Stainless Steel (CF8M/316), Aluminum (356) |
| Source 2 — supply media temperature range | Supply Media Temperature Range: -320° F to 300° F |
| Source 2 — drilling classes | 150# ANSI, PN10, PN16, JIS drilling classes available |
| Source 2 — pilot accessories | Pilot exhaust piped to discharge header, Field test connection, Manual blow down, Conical film seat pallet, Remote sense pickup, Pilot supply filter |
| Source 3 — Nominal valve connection size | Size 1/2” to 20” |
| Source 3 — Pressure Rating | Pressure Rating 150# x 150# to 2500# x 300# |
| Source 3 — End connection types | End Connection Flange End, Screwed End, Tri-Clover End |
| Source 3 — seat options | Seat Metal Seat / Soft Seat |
| Source 3 — orifice standard | Orifice As per API 520 |
| Source 3 — blowdown and overpressure | Blow Down <10% of Set Pressure, Over Pressure >10% of Set Pressure |
| Source 3 — Valve body material | Material Carbon steel, Stainless steel, Duplex-SS, nickel-molybdenum alloy, Alloy-20, nickel-copper alloy |
| Source 3 — pilot sensing design | Design - High Pressure, Semi- Nozzle/ Full- Nozzle, Piston Sensing Pilot |
| Source 3 — type options | Type Conventional, Balanced Bellow, Balance Piston, Pilot Operated, PTFE Lined |
| Source 4 — seat design options | Soft seat design: Provides repeatable bubble-tight performance before and after each relief cycle, Metal-to-metal seat design: Provides pilot valve performance in high temperature service |
| Source 4 — balanced design principle | Balanced design: Lift unaffected by back pressure; no expensive and fragile bellows required to balance against high back pressure |
| Source 4 — full lift dot maop capability | Full lift at set pressure: No overpressure required for full lift; allows D.O.T. installation to be set higher than Maximum Allowable Operating Pressure (MAOP) when pop action is used |
| Source 4 — replaceable seats and seals | Replaceable soft seats and seals: All seats and seals are renewable easily and quickly; no expensive, time-consuming seat lapping required |
| Source 4 — api526 center to face dimensions | API 526 direct spring center-to-face dimensions available for Series 200, 400, 500 and 800 pilots eliminating the need for piping modifications during upgrades |
| Source 4 — pop action cryogenic benefit | Pop action available: No main valve throttling, which helps prevent freeze-ups in cryogenic or refrigerant type services |
| Source 4 — modulating action benefits | Modulating action available: Significantly cut product loss per relief situation; reduce environmental pollution; avoid oversizing consequences; not as sensitive to inlet pressure losses as pop action |
範圍與來源備註
| back pressure capability tension | Back-pressure capability tension: the page spec states superimposed back pressure up to ~50% of set, while OEM documents state 70% consistent compensation (LESER, 95% in certain cases; Crosby 70% with backflow preventer); the ~50% figure should be owner-reviewed against per-configuration OEM limits. |
|---|---|
| pilot closure figures | Generic vendor pages describe pilot closure near 90% of set pressure; OEM pop-action figures are 97% (adjustable to 85%, blowdown -3% to -15%) - the OEM figures govern; generic-website numbers were excluded from this page. |
| set pressure envelope | Emerson Series 400 shows a 15-740 psig (about 1-51 barg) set-pressure envelope, so the page 0.1-10 MPa range is a tenant selection, not an industry ceiling; temperature envelope (-162 to 320 °C) sits against soft-seal limits where the manufacturer must be consulted at 200 °C and above - quote per configuration. |
訂購與文件
文件
請在詢問時一併說明您需要的文件組合——此結構的常見項目（材質證明、按所列檢驗標準的測試報告、尺寸圖）將於報價時確認並隨附供應。
報價
可直接報價的詢問應說明：公稱口徑與壓力額定、閥體與閥座材質偏好、端部連接、操作方式，以及含溫度的使用介質。本頁的典型值為基準參考範圍；具有約束力的數值於報價時確認。
樣品與供應
供應條件、訂購數量與交期按訂單議定——請在詢問時說明目的地國家與所需時程。
儲存與運輸
閥門儲存時應保護閥座與密封件免受紫外線、臭氧與變形影響，安裝前保留端面保護蓋；彈性體或 PTFE 閥座結構應避免長期戶外存放——閥座材料在陽光直射與冰凍條件下老化最快。
常見問題
先導式安全閥的報價詢問應包含哪些內容？
執行標準與壓力等級、公稱口徑、閥體與閥座材質、介質及溫度、目的地——缺失的資訊會在報價過程中確認。
先導式安全閥提供哪些口徑與壓力等級？
本頁面尚未公布該閥門經驗證的口徑與壓力等級範圍——適用於您工況的口徑與壓力等級會在報價過程中提出並確認。請在詢問時附上工況條件，選型結果會在報價中說明。
先導式安全閥提供哪些閥體材質？
本頁面尚未公布該閥門經驗證的閥體材質範圍——適用於您工況的閥體材質會在報價過程中提出並確認。請在詢問時附上工況條件，選型結果會在報價中說明。
請求先導式安全閥報價
在此提交需求——可直接報價的詢問應說明適用標準與等級、口徑、材質、介質、溫度與目的地.
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準備提出較大量或非標準需求？ 先導式安全閥詢價指南 說明應包含的內容、標準範圍與客製選項，以及應附上的文件。