止回阀是能自动阻止流体倒流的阀门。止回阀的阀瓣在流体压力作用下开启，流体从进口侧流向出口侧。当进口侧压力低于出口侧时，阀瓣在流体压差、本身重力等因素作用下自动关闭以防止流体倒流。
止回阀一般分为升降式、旋启式等几种类型。
升降式止回阀的结构一般与截止阀相似，其阀瓣沿着通道中心线作升降运动，动作可靠，但流体阻力较大，适用于较小口径的场合。升降式止回阀可分为直通式和立式两种。直通式升降式止回阀一般只能安装在水平管路，而立式升降止回阀一般应安装在垂直管路。
旋启式止回阀的阀瓣绕转轴作旋转运动。其流体阻力一般小于升降式止回阀，它适用于较大口径的场合。旋启式止回阀根据阀瓣的数目可分为单瓣旋启式、双瓣旋启式及多瓣旋启式三种。单瓣旋启式止回阀一般适用于中等口径的场合。大口径管路选用单瓣旋启式止回阀时，为减少水锤压力，采用能减小水锤压力的缓闭止回阀。双瓣旋启式止回阀适用于大中口径管路。对夹双瓣旋启式止回阀结构小、重量轻，是一种发展较快的止回阀；多瓣旋启式止回阀适用于大口径管道路。
主要零件材料及性能规范
| 主 要 零 部 件 | 阀体、阀盖、摇杆 | WCB | CF8 | CF8M | WC6、WC9 |
| 阀瓣 | WCB堆Cr13或硬质合金 | CF8堆硬质合金 | CF8M堆硬质合金 | WC6、WC9堆硬质合金 | |
| 阀座 | 25堆Cr13或硬质合金 | 304堆硬质合金 | 316堆硬质合金 | 20Cr1MoV堆硬质合金 | |
| 垫片 | 软铁、XB450 | 聚四氟乙烯 | 聚四氟乙烯 | 不锈钢+耐酸石棉缠绕垫 | |
| 螺栓 | 35CrMoA | 35CrMoA | 35CrMoA | 25Cr1Mo1V | |
| 螺母 | 45 | 45 | 45 | 35CrMoA | |
| 主要参数 | 适用介质 | 油品、水、蒸汽 | 硝酸类 | 醋酸类 | 油品、水、蒸汽 |
| 适用温度 ℃ | ≤425 | ≤200 | ≤200 | ≤550 |
| 型号 | 公称 通径 NPS(in) | 压力级 Class | 主要结构尺寸(mm) | 阀体 材料 | 性能规范 | |||||
| D | D1 | L | L1 | H | 适用温度(℃) | 适用介质 | ||||
| SFH | 2" | 150 | | | 203 | | 170 | WCB | ≤425 | 水、油品、蒸气等 |
| " | 3" | " | | | 241 | | 185 | " | " | " |
| " | 4" | " | | | 292 | | 215 | " | " | " |
| " | 6" | " | | | 356 | | 260 | " | " | " |
| " | 8" | " | | | 495 | | 300 | " | " | " |
| " | 10" | " | | | 622 | | 350 | " | " | " |
| " | 12" | " | | | 699 | | 400 | " | " | " |
| " | 14" | " | | | 787 | | 450 | " | " | " |
| " | 16" | " | | | 864 | | 480 | " | " | " |
| " | 18" | " | | | 978 | | 540 | " | " | " |
| " | 20" | " | | | 978 | | 600 | " | " | " |
| " | 24" | " | | | 1295 | | 680 | " | " | " |
| SFH | 2" | 300 | | | 267 | | 170 | WCB | ≤425 | 水、油品、蒸气等 |
| " | 3" | " | | | 318 | | 215 | " | " | " |
| " | 4" | " | | | 356 | | 235 | " | " | " |
| " | 6" | " | | | 445 | | 300 | " | " | " |
| " | 8" | " | | | 533 | | 340 | " | " | " |
| " | 10" | " | | | 622 | | 350 | " | " | " |
| " | 12" | " | | | 711 | | 420 | " | " | " |
| " | 14" | " | | | 838 | | 480 | " | " | " |
| " | 16" | " | | | 864 | | 520 | " | " | " |
| " | 18" | " | | | 978 | | 600 | " | " | " |
| " | 20" | " | | | 1016 | | 670 | " | " | " |
| " | 24" | " | | | 1346 | | 750 | " | " | " |
| SFH | 2" | 600 | | | 292 | | 175 | WCB | ≤425 | 水、油品、蒸气 |
| " | 3" | " | | | 356 | | 230 | " | " | " |
| " | 4" | " | | | 432 | | 295 | " | " | " |
| " | 6" | " | | | 559 | | 360 | " | " | " |
| " | 8" | " | | | 660 | | 400 | " | " | " |
| " | 10" | " | | | 787 | | 460 | " | " | " |
| " | 12" | " | | | 838 | | 520 | " | " | " |
| " | 14" | " | | | 889 | | 560 | " | " | " |
| " | 16" | " | | | 991 | | 650 | " | " | " |
| " | 18" | " | | | 1092 | | 730 | " | " | " |
| " | 20" | " | | | 1194 | | 800 | " | " | " |
| " | 24" | " | | | 1397 | | 900 | " | " | " |
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