止回閥是能自動(dòng)阻止流體倒流的閥門。止回閥的閥瓣在流體壓力作用下開啟，流體從進(jìn)口側(cè)流向出口側(cè)。當(dāng)進(jìn)口側(cè)壓力低于出口側(cè)時(shí)，閥瓣在流體壓差、本身重力等因素作用下自動(dòng)關(guān)閉以防止流體倒流。
止回閥一般分為升降式、旋啟式等幾種類型。
升降式止回閥的結(jié)構(gòu)一般與截止閥相似，其閥瓣沿著通道中心線作升降運(yùn)動(dòng)，動(dòng)作可靠，但流體阻力較大，適用于較小口徑的場(chǎng)合。升降式止回閥可分為直通式和立式兩種。直通式升降式止回閥一般只能安裝在水平管路，而立式升降止回閥一般應(yīng)安裝在垂直管路。
旋啟式止回閥的閥瓣繞轉(zhuǎn)軸作旋轉(zhuǎn)運(yùn)動(dòng)。其流體阻力一般小于升降式止回閥，它適用于較大口徑的場(chǎng)合。旋啟式止回閥根據(jù)閥瓣的數(shù)目可分為單瓣旋啟式、雙瓣旋啟式及多瓣旋啟式三種。單瓣旋啟式止回閥一般適用于中等口徑的場(chǎng)合。大口徑管路選用單瓣旋啟式止回閥時(shí)，為減少水錘壓力，采用能減小水錘壓力的緩閉止回閥。雙瓣旋啟式止回閥適用于大中口徑管路。對(duì)夾雙瓣旋啟式止回閥結(jié)構(gòu)小、重量輕，是一種發(fā)展較快的止回閥；多瓣旋啟式止回閥適用于大口徑管道路。
主要零件材料及性能規(guī)范
| 主 要 零 部 件 | 閥體、閥蓋、搖桿 | WCB | CF8 | CF8M | WC6、WC9 |
| 閥瓣 | WCB堆Cr13或硬質(zhì)合金 | CF8堆硬質(zhì)合金 | CF8M堆硬質(zhì)合金 | WC6、WC9堆硬質(zhì)合金 | |
| 閥座 | 25堆Cr13或硬質(zhì)合金 | 304堆硬質(zhì)合金 | 316堆硬質(zhì)合金 | 20Cr1MoV堆硬質(zhì)合金 | |
| 墊片 | 軟鐵、XB450 | 聚四氟乙烯 | 聚四氟乙烯 | 不銹鋼+耐酸石棉纏繞墊 | |
| 螺栓 | 35CrMoA | 35CrMoA | 35CrMoA | 25Cr1Mo1V | |
| 螺母 | 45 | 45 | 45 | 35CrMoA | |
| 主要參數(shù) | 適用介質(zhì) | 油品、水、蒸汽 | 硝酸類 | 醋酸類 | 油品、水、蒸汽 |
| 適用溫度 ℃ | ≤425 | ≤200 | ≤200 | ≤550 |
| 型號(hào) | 公稱 通徑 NPS(in) | 壓力級(jí) Class | 主要結(jié)構(gòu)尺寸(mm) | 閥體 材料 | 性能規(guī)范 | |||||
| D | D1 | L | L1 | H | 適用溫度(℃) | 適用介質(zhì) | ||||
| SFH-64C150C | 2" | 150 | | | 203 | | 170 | WCB | ≤425 | 水、油品、蒸氣等 |
| " | 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-64C300C | 2" | 300 | | | 267 | | 170 | WCB | ≤425 | 水、油品、蒸氣等 |
| " | 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-64C600C | 2" | 600 | | | 292 | | 175 | WCB | ≤425 | 水、油品、蒸氣 |
| " | 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 | " | " | " |
