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擴張式閘閥（expanding）

擴張式閘閥以機械方式密封：關閉時閘板組件向外擴張壓向兩側閥座，產生與管線壓力無關的雙向扭矩式密封，而組件在行程中於密封面之間自由移動以減少磨損、延長壽命——這是高溫高壓管線要求嚴密關斷時的選擇。產品範圍涵蓋 NPS 2" 至 12"（DN50 至 DN300），ASME Class 300 至 2500（PN40 至 PN420），閥體為碳鋼、不鏽鋼、合金鋼與雙相不鏽鋼，端接為 RF、BW 或 RTJ，操作為手動、氣動、電動或液動，設計依 API 6D。成就這些性能餘量的是設計細節：閥座環朝外，僅在端點位置接觸（凸輪固定的閘板段無摩擦移動，部分行程不磨損閥座）、密封僅靠閥桿推力壓緊——即使零壓差也雙向氣泡級密封，無需壓力助封——且全開通徑為連續通道，可通清管器且壓降如直管。關閉時同時密封兩側閥座，兩者之間的腔體可排放或排空，實現雙阻塞排放（DBB）隔斷。典型失效路徑為液體服務中的腔體熱超壓（應加裝腔體洩壓並保持針閥開啟）、調試雜物刮傷閥座嵌件（啟動前沖洗並清潔循環管線），以及填料過度緊固使本已偏高的楔式扭矩再加劇。在水平管線上直立安裝、手輪位於中心線上方，安裝前全開/全關活動閥門以發現閘板機構阻礙，並將兩個閥體中部注射口（保持在管線壓力以上約 300 psi 內）僅作緊急輔助密封，閥蓋排空口用於驗證關閉後腔體已洩壓。注意兩套 API 框架：API 6D 管線閥採 ISO 5208 洩漏等級（面距 API 6D/ASME B16.10、對焊端 B16.25、額定 B16.34），較小的井口閥則屬 API 6A——兩者不可互換。選型取決於尺寸段對管線、壓力等級對峰值壓力，以及閥座範圍對關斷任務的匹配。

屬於閘閥系列

最後更新： 2026-11

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系列規格

Nominal valve connection size	NPS 2"~12"(DN50~DN300）
Pressure class / nominal rating designation	ASME CLASS 300~2500（PN40~PN420）
Valve body material	Carbon steel, Stainless steel, Alloy steel, Duplex stainless steel
End connection types	RF, BW, RTJ
Operation / closure mode	Manual, Pneumatic, Electric, Hydraulic
Design standards	API 6D
selection seat ring life vs slab	Compared with a slab gate valve of the same size, an expanding gate design gives the full-bore pigging conduit together with longer seat-ring seal life, because the seat faces engage with the gate only near the end of travel rather than rubbing throughout the stroke.
selection torque tightened bidirectional seal	The two-segment gate is expanded against both seats by the stem/handwheel thrust, so the mechanical seal tightens as operating torque increases and does not depend on line pressure to energize it; this makes the shut-off bidirectional and relatively insensitive to pressure surges and vibration.
selection full bore pigging conduit	In the fully open position the gate segments retract into the body so the bore becomes a continuous cylindrical conduit, allowing pipeline pigs and scrapers to pass and keeping turbulence and pressure drop close to that of an equal length of pipe.
selection double block and bleed	In the closed position the expanded gate seals simultaneously against both the upstream and downstream seats, so the body cavity between the seats can be drained or vented, giving a double-block-and-bleed isolation function from a single valve.
selection seat faces shielded from flow	The seat rings are oriented to face outward so they contact the flow medium as little as possible and engage fully with the gate only at the end positions; this shielding of the sealing faces is a main reason expanding gates tolerate abrasive or debris-laden service better than wedge gates.
selection cam locks segments during travel	A cam/guide mechanism holds the two gate segments against expansion while the gate is mid-stroke: the assembly slides without seat friction during travel and expands only at the fully open or fully closed position, which protects the seats from wear during partial stroking.
selection stem thrust not pressure energized	Bubble-tight isolation is achieved upstream and downstream simultaneously purely through stem thrust on the wedge slopes; no line-pressure energizing of the seal is required, so sealing performance is maintained at low or zero differential pressure.
selection temperature envelope	Standard material trim covers roughly -29 C to 190 C service with low-temperature and extended-temperature options beyond that; published envelopes differ widely between makers, so the applicable temperature window must be confirmed against the specific body/seat materials rather than the generic design.
failure thermal cavity overpressure liquid service	With the gate expanded and both seats sealed, trapped liquid in the body cavity can build dangerous overpressure when the line warms up; valves for liquid service must therefore be fitted with a functioning thermal cavity relief system, and any needle valves in that circuit must be open before operation.
failure debris damages seat inserts	Scale, welding slag and other foreign material left in the pipeline are a leading cause of seat leakage at commissioning: debris packed between the gate segments and seat faces scratches the inserts. The line must be flushed and the valve cycled clean before it is put into service.
failure pre install cycle check for obstruction	Before installation the valve should be fully opened and closed once; if any abnormal resistance is felt, operation must stop and the stem and bore inspected for obstructions, since debris jammed in the gate-segment mechanism is easier to remove on the bench than in-line.
failure gland overtightening raises torque	Over-compressing the stem packing shortens packing life and noticeably raises operating torque, which matters for an expanding gate where the handwheel already works against wedge friction; the gland should be tightened only enough to stop leakage.
installation upright orientation recommended	The standard mounting is on a horizontal line with the stem vertical and the handwheel above the valve centerline, which keeps the gate-segment assembly aligned and supported; some makers qualify other orientations, and horizontal-stem or vertical-line installations require special design or tooling.
installation secondary sealant injection ports	Two sealant/lubricant injection ports in the body mid-section allow an approved sealant to be injected to the seat-gate interface as an emergency secondary seal if the sealing surfaces are damaged and leaking; injection pressure is kept within about 300 psi above line pressure.
installation cavity bleed via bonnet vent	With the valve fully closed, body-cavity pressure can be vented through the bonnet vent fitting (operator standing clear of the vent), and bottom drain plugs allow flushed-out debris to be removed; this gives a routine way to prove cavity depressurization after double-block-and-bleed closure.
standards api 6d vs api 6a envelopes	Expanding gate valves are made to two distinct API frames: pipeline valves to API 6D (roughly NPS 2-36, ASME Class 300-2500) and wellhead valves to API 6A (smaller bores at 2000-15000 psi working pressures); a 6D valve is not interchangeable with a 6A valve of similar size.
standards leakage testing iso 5208 api6d	Acceptance leakage testing for API 6D expanding gate valves is specified against ISO 5208 leakage-rate classes (with API 6D setting the class requirements per service), in addition to the standard hydrostatic shell and seat tests.
standards design codes b16 34 face to face	Pressure-boundary dimensions follow ASME B16.34 for pressure-temperature ratings, with face-to-face to API 6D/ASME B16.10, butt-weld ends to ASME B16.25, and welded-end/adapting-flange dimensions to ASME B16.34/MSS SP-44.
special features	Bi-directional torque based mechanical seal, Gate assembly travels freely between the seal surfaces which reduces the wear risk and prolongs the valve service life
applications	High temperature and high pressure pipelines

範圍與來源備註

temperature envelope disagreement	Temperature envelope disagreement: one OEM states -29 to 190 C standard (low-temp option to -46 C) while another claims -196 to +649 C working temperature; the wide claim likely reflects special trims and must not be used as the generic envelope.
orientation guidance differs	Orientation guidance differs: one OEM IOM recommends upright installation (handwheel above centerline), another states vertical as designed but horizontal acceptable, and a third offers special horizontal-stem/vertical-line designs; present as upright preferred with other orientations per manufacturer qualification.
torque comparison tension	Torque comparison tension: one OEM claims lower operating torque than an equivalent slab gate while the expanding design also deliberately uses higher seating torque to mechanically expand the gate - the statements refer to different points in the stroke and must not be merged into a single torque claim.