{"id":8360,"date":"2026-06-04T17:41:23","date_gmt":"2026-06-04T17:41:23","guid":{"rendered":"https:\/\/www.yunrui-controls.com\/?p=8360"},"modified":"2026-06-04T17:41:23","modified_gmt":"2026-06-04T17:41:23","slug":"valve-stem-sealing-method","status":"publish","type":"post","link":"https:\/\/www.yunrui-controls.com\/ja\/valve-stem-sealing-method\/","title":{"rendered":"\u9069\u5207\u306a\u30d0\u30eb\u30d6\u30b9\u30c6\u30e0\u30b7\u30fc\u30eb\u65b9\u6cd5\u306e\u9078\u629e"},"content":{"rendered":"

What is Valve Stem Sealing?<\/h2>\n

Control valves and on-off valves typically fall into one of two categories: linear<\/strong> \u307e\u305f\u306f rotary<\/strong>. Linear valves have a stem that extends from the valve body, rising and falling to drive the valve open and closed. Rotary valves have a stem connected to a plug, disc, or ball. When the stem rotates, it opens and closes the valve. In both designs, the stem moves within the valve body with relatively low friction while also contacting the process medium.<\/p>\n

Measuring Valve Stem Seal Performance<\/h2>\n

Three major industrial standards measure valve stem leakage: TA Luft<\/strong>, FCI 91-1<\/strong>, and ISO 15848<\/strong>. However, each standard differs significantly in testing performance and methodology.<\/p>\n

TA Luft<\/strong> is the earliest standard, providing leakage rate criteria without detailed specifications for test parameter classification.<\/p>\n

FCI 91-1<\/strong> aligns more closely with EPA’s LDAR program and uses EPA Method 21 to “sniff” valve packing and determine leakage rates. This standard provides valve testing methods and various classification ratings based on stem leakage rates after specified numbers of mechanical and thermal cycles.<\/p>\n

ISO 15848<\/strong> covers a broader scope, classifying several leakage rates for control and on-off valves based on mechanical cycles, thermal cycles, and stem size. It allows testing with helium or methane and specifies precise methods for measuring leakage.<\/p>\n

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\u91cd\u8981\uff1a<\/strong> When comparing valve stem seal performance, it is crucial to first determine which standard was used for valve testing. Achieving very low leakage rates is relatively easy with fewer mechanical cycles. Maintaining very low leakage rates becomes much more difficult when valves undergo thousands of mechanical cycles while experiencing thermal cycling.<\/p>\n<\/div>\n

Packing Seal Valve Stems<\/h2>\n

Most valves use PTFE or graphite sealing rings<\/strong> to provide stem sealing. A combination of packing gland, packing gland flange, and bolts compresses the sealing rings, pushing the packing rings down against the stem. This design allows stem movement while preventing process medium from escaping.<\/p>\n

To achieve and maintain low stem leakage, packing should use “live loading”<\/strong> to maintain constant pressure on the sealing rings. Fisher’s<\/a> ENVIRO-SEAL\u2122 packing<\/strong> uses compressed disc springs to maintain constant pressure on the packing rings, ensuring seal integrity even after stem movement wear. However, increased pressure tends to restrict valve movement, so sealing materials and stem finish must be carefully selected.<\/p>\n

Bellows Seal Valve Stems<\/h2>\n

Another option is the bellows seal valve<\/strong>. Bellows sealing utilizes a welded or mechanically formed metal barrier around the stem that compresses and extends like an accordion. This bellows-style metal seal achieves zero leakage<\/strong>.<\/p>\n

Bellows seals use two main types:<\/p>\n