اتصل بنا مهندس شاب الشهر الماضي. كان يكتب مواصفات الصمام لمشروع جديد. سأل: "كم عدد فئات التسرب الموجودة؟? أرى أ, ب, ج, د, وبعض الفئة أ, ب, ج من معيار آخر. هل هم نفس الشيء?"
لا. إنهم ليسوا نفس الشيء.
في مجموعة تكنولوجيا السوائل, we get this question often. Industrial Valve leakage standards can be confusing because different standards cover different types of leakage. One standard covers seat leakage (through the closed valve). Another covers fugitive emissions (leakage to the atmosphere). They use similar letters but mean different things.
This article lists every leakage class you need to know. I will explain what each level means, where it applies, and how to choose the right one.
جزء 1: Seat leakage classes (ايزو 5208 / GB/T 13927)
This standard measures leakage through the valve seat when the valve is fully closed. It has four classes: أ, ب, ج, and D.
Important rule: Classes B, ج, and D only apply to metal hard-seated valves. Soft-seal valves (ممحاة, PTFE, إبدم) are always Class A – zero visible leakage.
| فصل | Liquid leakage limit | Gas leakage limit | طلب |
| Class A | Zero visible leakage | Zero visible leakage | Soft-seal valves, bellows seal valves |
| Class B | ≤ 0.01 × DN (mm³/s) | ≤ 0.3 × DN (mm³/s) | Precision metal hard-seated valves – high accuracy |
| Class C | ≤ 0.03 × DN (mm³/s) | ≤ 3 × DN (mm³/s) | High-temperature metal hard-seated valves – moderate accuracy |
| Class D | ≤ 0.1 × DN (mm³/s) | ≤ 30 × DN (mm³/s) | General purpose metal hard-seated valves – default class |
Which one should you choose?
| فصل | When to use | Typical applications |
| Class A | When zero leakage is critical | الحماية من الحرائق, يشرب الماء, clean applications – any soft-seal valve |
| Class B | When leakage must be extremely low | High-pressure gas, precision control systems, expensive media |
| Class C | When leakage is acceptable but limited | High-temperature steam, thermal oil, hot flue gas, general industrial |
| Class D | When no special requirement exists | Standard water lines, low-pressure systems, general cast steel valves |
جزء 2: Fugitive emission classes (ايزو 15848)
This standard measures leakage from the valve stem packing to the atmosphere. It has three classes: أ, ب, and C.
| فصل | Leakage limit (helium test) | Practical equivalent | طلب |
| Class C | ≤ 10⁻² mg/(s·m) | Stem ≤ 500 ppmv; Body ≤ 10 ppmv | Ordinary steam, مياه التبريد, non-toxic media |
| Class B | ≤ 10⁻³ mg/(s·m) | Tighter than Class C | البتروكيماويات, النفط والغاز, moderate VOC control |
| Class A | ≤ 10⁻⁴ mg/(s·m) | Tightest – near zero emission | Toxic gas, highly volatile media, strict environmental compliance |
What packing do you need?
| فصل | Packing requirement |
| Class C | Standard flexible graphite packing |
| Class B | High-performance packing, advanced graphite or PTFE |
| Class A | Bellows seals or high-purity PTFE low-emission packing |
Summary table – all leakage classes at a glance
| معيار | فصل | What it measures | Leakage level |
| ايزو 5208 / GB/T 13927 | أ | Seat leakage (soft seal) | Zero visible leakage |
| ايزو 5208 / GB/T 13927 | ب | Seat leakage (مقعد معدني) | Very tight – precision grade |
| ايزو 5208 / GB/T 13927 | ج | Seat leakage (مقعد معدني) | Moderate – industrial grade |
| ايزو 5208 / GB/T 13927 | د | Seat leakage (مقعد معدني) | Loose – general purpose |
| ايزو 15848 | أ | Fugitive emission (ينبع) | Near zero – strict environmental |
| ايزو 15848 | ب | Fugitive emission (ينبع) | Tight – moderate environmental |
| ايزو 15848 | ج | Fugitive emission (ينبع) | Basic – entry level low emission |
Three quick rules to avoid mistakes
Rule 1 – Soft-seal valves are always Class A in seat leakage. Do not specify B, ج, or D. They do not apply. If your valve has a rubber, PTFE, or EPDM seat, it leaks zero through the seat.
Rule 2 – The two “Class C” are different. One is internal seat leakage. One is external stem leakage. They test different things, use different standards, and serve different applications.
Rule 3 – Default is not always good. Standard cast steel صمامات البوابة usually come as Class D seat leakage. If you need tighter sealing, you must specify Class C or B. The price goes up – but the performance improves.
What Fluid Tech Group does for you
We supply valves for fire protection and water systems. We know these standards because we work with them every day.
We supply soft-seal valves with ISO 5208 Class A – no visible leakage through the seat.
We supply metal-seated valves with Class B, ج, or D based on your project requirements.
We supply ISO 15848 Class A, ب, or C for fugitive emission control – with test reports.
We ask the right questions before we quote – so you get the right class the first time.
Your next step
Send us your valve requirements. Tell us your media, درجة حرارة, ضغط, and any environmental regulations. We will recommend the correct leakage class and provide a quotation with test documentation.
مجموعة تكنولوجيا السوائل
Valve leakage classes – we speak all of them