化工儀器網(wǎng)
詳細(xì)介紹
費(fèi)斯托減壓閥的出口壓力是用來(lái)控制電液換向閥或外控順序閥等的控制油液壓力大小的，當(dāng)電液換向閥或外控順序閥換向或工作后,，減壓閥出油口流量變?yōu)榱悖珘毫€需保持原先調(diào)定的壓力,。這種情況下,，因閥出口流量為零,，流經(jīng)減壓口的流量只有先導(dǎo)流量。由于先導(dǎo)流量很少,，一般在2L/min之內(nèi),，因此主閥減壓口基本上接近全關(guān)位置（開(kāi)度極小）,，先導(dǎo)流量由三角槽或斜錐面處流出,，如果主閥芯配合過(guò)松或磨損過(guò)大，則泄漏量增加,。按流量連續(xù)性定理,，這部分泄漏量也必須從主閥芯阻尼孔流來(lái)，即流經(jīng)阻尼孔的流量由先導(dǎo)流量和泄漏量?jī)刹糠謽?gòu)成,，而阻尼孔面積和主閥彈簧腔油液壓力未變（彈簧腔油液壓力由已調(diào)好的調(diào)壓彈簧預(yù)壓縮量確定）,，為使通過(guò)阻尼孔的流量增加,，必然引起主閥下腔油液壓力的升高。因此,，當(dāng)減壓閥出口壓力調(diào)定后,，如果出口流量為零時(shí)，出口壓力會(huì)因主閥芯配合過(guò)松或磨損過(guò)大而升高,。 194704 LFRS-1/8-D-5M-MINI G1/8 650 l/min 0.5 ... 12 bar 5 µm
194706 LFRS-1/8-D-5M-MINI-A G1/8 650 l/min 0.5 ... 12 bar 5 µm
194705 LFRS-1/8-D-5M-O-MINI G1/8 650 l/min 0.5 ... 12 bar 5 µm
194707 LFRS-1/8-D-5M-O-MINI-A G1/8 650 l/min 0.5 ... 12 bar 5 µm
194700 LFRS-1/8-D-7-MINI G1/8 900 l/min 0.5 ... 7 bar 40 µm
194702 LFRS-1/8-D-7-MINI-A G1/8 900 l/min 0.5 ... 7 bar 40 µm
194701 LFRS-1/8-D-7-O-MINI G1/8 900 l/min 0.5 ... 7 bar 40 µm
194703 LFRS-1/8-D-7-O-MINI-A G1/8 900 l/min 0.5 ... 7 bar 40 µm
194696 LFRS-1/8-D-MINI G1/8 750 l/min 0.5 ... 12 bar 40 µm
194697 LFRS-1/8-D-MINI-A G1/8 750 l/min 0.5 ... 12 bar 40 µm
194698 LFRS-1/8-D-O-MINI G1/8 750 l/min 0.5 ... 12 bar 40 µm
194699 LFRS-1/8-D-O-MINI-A G1/8 750 l/min 0.5 ... 12 bar 40 µm
194716 LFRS-1/4-D-5M-MINI G1/4 1200 l/min 0.5 ... 12 bar 5 µm
194718 LFRS-1/4-D-5M-MINI-A G1/4 1200 l/min 0.5 ... 12 bar 5 µm
194717 LFRS-1/4-D-5M-O-MINI G1/4 1200 l/min 0.5 ... 12 bar 5 µm
194719 LFRS-1/4-D-5M-O-MINI-A G1/4 1200 l/min 0.5 ... 12 bar 5 µm
194712 LFRS-1/4-D-7-MINI G1/4 1500 l/min 0.5 ... 7 bar 40 µm
194714 LFRS-1/4-D-7-MINI-A G1/4 1500 l/min 0.5 ... 7 bar 40 µm
194713 LFRS-1/4-D-7-O-MINI G1/4 1500 l/min 0.5 ... 7 bar 40 µm
194715 LFRS-1/4-D-7-O-MINI-A G1/4 1500 l/min 0.5 ... 7 bar 40 µm
194708 LFRS-1/4-D-MINI G1/4 1400 l/min 0.5 ... 12 bar 40 µm
194709 LFRS-1/4-D-MINI-A G1/4 1400 l/min 0.5 ... 12 bar 40 µm
194710 LFRS-1/4-D-O-MINI G1/4 1400 l/min 0.5 ... 12 bar 40 µm
194711 LFRS-1/4-D-O-MINI-A G1/4 1400 l/min 0.5 ... 12 bar 40 µm
194740 LFRS-1/4-D-5M-MIDI G1/4 1600 l/min 0.5 ... 12 bar 5 µm
194742 LFRS-1/4-D-5M-MIDI-A G1/4 1600 l/min 0.5 ... 12 bar 5 µm
194741 LFRS-1/4-D-5M-O-MIDI G1/4 1600 l/min 0.5 ... 12 bar 5 µm
194743 LFRS-1/4-D-5M-O-MIDI-A G1/4 1600 l/min 0.5 ... 12 bar 5 µm
194736 LFRS-1/4-D-7-MIDI G1/4 2100 l/min 0.5 ... 7 bar 40 µm
194738 LFRS-1/4-D-7-MIDI-A G1/4 2100 l/min 0.5 ... 7 bar 40 µm
費(fèi)斯托減壓閥調(diào)壓步驟
1,、關(guān)閉減壓閥前的閘閥，開(kāi)啟減壓閥后的閘閥,，制造下游低壓環(huán)境；
2,、將調(diào)節(jié)螺釘按逆時(shí)針旋轉(zhuǎn)至zui上位置（相對(duì)zui低出口壓力）,，然后關(guān)閉減壓閥后閘閥,；
3,、慢慢開(kāi)啟減壓閥前的閘閥至全開(kāi),；
4,、順時(shí)針慢慢旋轉(zhuǎn)調(diào)節(jié)螺釘,，將出口壓力調(diào)至所需要的壓力（以閥后表壓為準(zhǔn)）,；調(diào)整好后,，將鎖緊
螺母鎖緊,，打開(kāi)減壓閥后閘閥,；
5,、如在調(diào)整時(shí)出口壓力高于設(shè)定壓力,，須從*步開(kāi)始重新調(diào)整,，即只能從低壓向高壓調(diào)。194737 LFRS-1/4-D-7-O-MIDI G1/4 2100 l/min 0.5 ... 7 bar 40 µm
194739 LFRS-1/4-D-7-O-MIDI-A G1/4 2100 l/min 0.5 ... 7 bar 40 µm
194732 LFRS-1/4-D-MIDI G1/4 2000 l/min 0.5 ... 12 bar 40 µm
194733 LFRS-1/4-D-MIDI-A G1/4 2000 l/min 0.5 ... 12 bar 40 µm
194734 LFRS-1/4-D-O-MIDI G1/4 2000 l/min 0.5 ... 12 bar 40 µm
194735 LFRS-1/4-D-O-MIDI-A G1/4 2000 l/min 0.5 ... 12 bar 40 µm
194728 LFRS-3/8-D-5M-MINI G3/8 1350 l/min 0.5 ... 12 bar 5 µm
194730 LFRS-3/8-D-5M-MINI-A G3/8 1350 l/min 0.5 ... 12 bar 5 µm
194729 LFRS-3/8-D-5M-O-MINI G3/8 1350 l/min 0.5 ... 12 bar 5 µm
194731 LFRS-3/8-D-5M-O-MINI-A G3/8 1350 l/min 0.5 ... 12 bar 5 µm
194724 LFRS-3/8-D-7-MINI G3/8 1700 l/min 0.5 ... 7 bar 40 µm
194726 LFRS-3/8-D-7-MINI-A G3/8 1700 l/min 0.5 ... 7 bar 40 µm
194725 LFRS-3/8-D-7-O-MINI G3/8 1700 l/min 0.5 ... 7 bar 40 µm
194727 LFRS-3/8-D-7-O-MINI-A G3/8 1700 l/min 0.5 ... 7 bar 40 µm
194720 LFRS-3/8-D-MINI G3/8 1600 l/min 0.5 ... 12 bar 40 µm
194721 LFRS-3/8-D-MINI-A G3/8 1600 l/min 0.5 ... 12 bar 40 µm
194722 LFRS-3/8-D-O-MINI G3/8 1600 l/min 0.5 ... 12 bar 40 µm
194723 LFRS-3/8-D-O-MINI-A G3/8 1600 l/min 0.5 ... 12 bar 40 µm
194752 LFRS-3/8-D-5M-MIDI G3/8 2400 l/min 0.5 ... 12 bar 5 µm
194754 LFRS-3/8-D-5M-MIDI-A G3/8 2400 l/min 0.5 ... 12 bar 5 µm
194753 LFRS-3/8-D-5M-O-MIDI G3/8 2400 l/min 0.5 ... 12 bar 5 µm
194755 LFRS-3/8-D-5M-O-MIDI-A G3/8 2400 l/min 0.5 ... 12 bar 5 µm
194748 LFRS-3/8-D-7-MIDI G3/8 3200 l/min 0.5 ... 7 bar 40 µm
194750 LFRS-3/8-D-7-MIDI-A G3/8 3200 l/min 0.5 ... 7 bar 40 µm
194749 LFRS-3/8-D-7-O-MIDI G3/8 3200 l/min 0.5 ... 7 bar 40 µm
194751 LFRS-3/8-D-7-O-MIDI-A G3/8 3200 l/min 0.5 ... 7 bar 40 µm
194744 LFRS-3/8-D-MIDI G3/8 3100 l/min 0.5 ... 12 bar 40 µm
194745 LFRS-3/8-D-MIDI-A G3/8 3100 l/min 0.5 ... 12 bar 40 µm
194746 LFRS-3/8-D-O-MIDI G3/8 3100 l/min 0.5 ... 12 bar 40 µm
194747 LFRS-3/8-D-O-MIDI-A G3/8 3100 l/min 0.5 ... 12 bar 40 µm
194764 LFRS-1/2-D-5M-MIDI G1/2 2600 l/min 0.5 ... 12 bar 5 µm
194766 LFRS-1/2-D-5M-MIDI-A G1/2 2600 l/min 0.5 ... 12 bar 5 µm
194765 LFRS-1/2-D-5M-O-MIDI G1/2 2600 l/min 0.5 ... 12 bar 5 µm
194767 LFRS-1/2-D-5M-O-MIDI-A G1/2 2600 l/min 0.5 ... 12 bar 5 µm
FESTO減壓閥基本性能：
(1)調(diào)壓范圍：它是指減壓閥輸出壓力P2的可調(diào)范圍,，在此范圍內(nèi)要求達(dá)到規(guī)定的精度,。調(diào)壓范圍主要與調(diào)壓彈簧的剛度有關(guān)。
(2)壓力特性：它是指流量g為定值時(shí),，因輸入壓力波動(dòng)而引起輸出壓力波動(dòng)的特性,。輸出壓力波動(dòng)越小，減壓閥的特性越好,。輸出壓力必須低于輸入壓力—定值才基本上不隨輸入壓力變化而變化,。
(3)流量特性：它是指輸入壓力—定時(shí)，輸出壓力隨輸出流量g的變化而變化的持性,。當(dāng)流量g發(fā)生變化時(shí),，輸出壓力的變化越小越好。一般輸出壓力越低,，它隨輸出流量的變化波動(dòng)就越小,。194760 LFRS-1/2-D-7-MIDI G1/2 3900 l/min 0.5 ... 7 bar 40 µm
194762 LFRS-1/2-D-7-MIDI-A G1/2 3900 l/min 0.5 ... 7 bar 40 µm
194761 LFRS-1/2-D-7-O-MIDI G1/2 3900 l/min 0.5 ... 7 bar 40 µm
194763 LFRS-1/2-D-7-O-MIDI-A G1/2 3900 l/min 0.5 ... 7 bar 40 µm
194756 LFRS-1/2-D-MIDI G1/2 3400 l/min 0.5 ... 12 bar 40 µm
194757 LFRS-1/2-D-MIDI-A G1/2 3400 l/min 0.5 ... 12 bar 40 µm
194758 LFRS-1/2-D-O-MIDI G1/2 3400 l/min 0.5 ... 12 bar 40 µm
194759 LFRS-1/2-D-O-MIDI-A G1/2 3400 l/min 0.5 ... 12 bar 40 µm
194818 LFRS-1/2-D-5M-DI-MAXI G1/2 4000 l/min 0.5 ... 12 bar 5 µm
194836 LFRS-1/2-D-5M-DI-MAXI-A G1/2 4000 l/min 0.5 ... 12 bar 5 µm
194788 LFRS-1/2-D-5M-MAXI G1/2 7500 l/min 0.5 ... 12 bar 5 µm
194790 LFRS-1/2-D-5M-MAXI-A G1/2 7500 l/min 0.5 ... 12 bar 5 µm
194819 LFRS-1/2-D-5M-O-DI-MAXI G1/2 4000 l/min 0.5 ... 12 bar 5 µm
194837 LFRS-1/2-D-5M-O-DI-MAXI-A G1/2 4000 l/min 0.5 ... 12 bar 5 µm
194789 LFRS-1/2-D-5M-O-MAXI G1/2 7500 l/min 0.5 ... 12 bar 5 µm
194791 LFRS-1/2-D-5M-O-MAXI-A G1/2 7500 l/min 0.5 ... 12 bar 5 µm
194820 LFRS-1/2-D-7-DI-MAXI G1/2 7600 l/min 0.5 ... 7 bar 40 µm
194838 LFRS-1/2-D-7-DI-MAXI-A G1/2 7600 l/min 0.5 ... 7 bar 40 µm
194784 LFRS-1/2-D-7-MAXI G1/2 9500 l/min 0.5 ... 7 bar 40 µm
194786 LFRS-1/2-D-7-MAXI-A G1/2 9500 l/min 0.5 ... 7 bar 40 µm
194821 LFRS-1/2-D-7-O-DI-MAXI G1/2 7600 l/min 0.5 ... 7 bar 40 µm
194839 LFRS-1/2-D-7-O-DI-MAXI-A G1/2 7600 l/min 0.5 ... 7 bar 40 µm
194785 LFRS-1/2-D-7-O-MAXI G1/2 9500 l/min 0.5 ... 7 bar 40 µm
194787 LFRS-1/2-D-7-O-MAXI-A G1/2 9500 l/min 0.5 ... 7 bar 40 µm
194816 LFRS-1/2-D-DI-MAXI G1/2 4500 l/min 0.5 ... 12 bar 40 µm
194834 LFRS-1/2-D-DI-MAXI-A G1/2 4500 l/min 0.5 ... 12 bar 40 µm
194780 LFRS-1/2-D-MAXI G1/2 9400 l/min 0.5 ... 12 bar 40 µm
194781 LFRS-1/2-D-MAXI-A G1/2 9400 l/min 0.5 ... 12 bar 40 µm
194817 LFRS-1/2-D-O-DI-MAXI G1/2 4500 l/min 0.5 ... 12 bar 40 µm
194835 LFRS-1/2-D-O-DI-MAXI-A G1/2 4500 l/min 0.5 ... 12 bar 40 µm
194782 LFRS-1/2-D-O-MAXI G1/2 9400 l/min 0.5 ... 12 bar 40 µm
194783 LFRS-1/2-D-O-MAXI-A G1/2 9400 l/min 0.5 ... 12 bar 40 µm
194776 LFRS-3/4-D-5M-MIDI G3/4 2600 l/min 0.5 ... 12 bar 5 µm
194778 LFRS-3/4-D-5M-MIDI-A G3/4 2600 l/min 0.5 ... 12 bar 5 µm
194777 LFRS-3/4-D-5M-O-MIDI G3/4 2600 l/min 0.5 ... 12 bar 5 µm
194779 LFRS-3/4-D-5M-O-MIDI-A G3/4 2600 l/min 0.5 ... 12 bar 5 µm
194772 LFRS-3/4-D-7-MIDI G3/4 4000 l/min 0.5 ... 7 bar 40 µm
194774 LFRS-3/4-D-7-MIDI-A G3/4 4000 l/min 0.5 ... 7 bar 40 µm
194773 LFRS-3/4-D-7-O-MIDI G3/4 4000 l/min 0.5 ... 7 bar 40 µm
194775 LFRS-3/4-D-7-O-MIDI-A G3/4 4000 l/min 0.5 ... 7 bar 40 µm
194768 LFRS-3/4-D-MIDI G3/4 3400 l/min 0.5 ... 12 bar 40 µm
194769 LFRS-3/4-D-MIDI-A G3/4 3400 l/min 0.5 ... 12 bar 40 µm
194770 LFRS-3/4-D-O-MIDI G3/4 3400 l/min 0.5 ... 12 bar 40 µm
194771 LFRS-3/4-D-O-MIDI-A G3/4 3400 l/min 0.5 ... 12 bar 40 µm
194824 LFRS-3/4-D-5M-DI-MAXI G3/4 5800 l/min 0.5 ... 12 bar 5 µm
194842 LFRS-3/4-D-5M-DI-MAXI-A G3/4 5800 l/min 0.5 ... 12 bar 5 µm
194800 LFRS-3/4-D-5M-MAXI G3/4 7600 l/min 0.5 ... 12 bar 5 µm
194802 LFRS-3/4-D-5M-MAXI-A G3/4 7600 l/min 0.5 ... 12 bar 5 µm
194825 LFRS-3/4-D-5M-O-DI-MAXI G3/4 5800 l/min 0.5 ... 12 bar 5 µm
194843 LFRS-3/4-D-5M-O-DI-MAXI-A G3/4 5800 l/min 0.5 ... 12 bar 5 µm
194801 LFRS-3/4-D-5M-O-MAXI G3/4 7600 l/min 0.5 ... 12 bar 5 µm
194803 LFRS-3/4-D-5M-O-MAXI-A G3/4 7600 l/min 0.5 ... 12 bar 5 µm
194826 LFRS-3/4-D-7-DI-MAXI G3/4 7700 l/min 0.5 ... 7 bar 40 µm
費(fèi)斯托比例式減壓閥的安裝位置。高層內(nèi)減壓閥設(shè)計(jì)安裝的位置不妥,，會(huì)出現(xiàn)減壓閥閥后壓力忽高忽低,，管網(wǎng)壓力嚴(yán)重偏離允許范圍，伴隨毀壞淋浴器,，水管爆裂和損壞用戶(hù)水表等事故發(fā)生,；有時(shí)也會(huì)水流不暢，分區(qū)內(nèi)出現(xiàn)無(wú)規(guī)律的斷水現(xiàn)象,，影響用戶(hù)用水,。出現(xiàn)類(lèi)似事故，檢查整個(gè)減壓閥減壓分區(qū)給水系統(tǒng),，無(wú)疑點(diǎn)可找,；拆卸減壓閥過(guò)濾器等元件并無(wú)異常；有些物業(yè)管理單位甚至懷疑減壓閥的技術(shù)性能,，多次調(diào)換新的減壓閥,，也不能解決問(wèn)題。這時(shí)可從檢查比例減壓閥設(shè)計(jì)安裝位置是否合理著手，認(rèn)真檢查管網(wǎng)系統(tǒng)是否存在等位倒虹管現(xiàn)象,，即分區(qū)的輸出管路標(biāo)高相近,。此類(lèi)情況在主、副樓同一屋頂水箱,，下給水供水系統(tǒng)中很容易出現(xiàn),。發(fā)現(xiàn)這些問(wèn)題，可以考慮把比例減壓閥安裝位置提高一個(gè)層面(不能提得太高,，必須顧全分區(qū)內(nèi)用水設(shè)備的承壓規(guī)范要求),；也可在主、副樓內(nèi),，分設(shè)兩組獨(dú)立的比例減壓閥給水系統(tǒng),。194844 LFRS-3/4-D-7-DI-MAXI-A G3/4 7700 l/min 0.5 ... 7 bar 40 µm
194796 LFRS-3/4-D-7-MAXI G3/4 10000 l/min 0.5 ... 7 bar 40 µm
194798 LFRS-3/4-D-7-MAXI-A G3/4 10000 l/min 0.5 ... 7 bar 40 µm
194827 LFRS-3/4-D-7-O-DI-MAXI G3/4 7700 l/min 0.5 ... 7 bar 40 µm
194845 LFRS-3/4-D-7-O-DI-MAXI-A G3/4 7700 l/min 0.5 ... 7 bar 40 µm
194797 LFRS-3/4-D-7-O-MAXI G3/4 10000 l/min 0.5 ... 7 bar 40 µm
194799 LFRS-3/4-D-7-O-MAXI-A G3/4 10000 l/min 0.5 ... 7 bar 40 µm
194822 LFRS-3/4-D-DI-MAXI G3/4 6800 l/min 0.5 ... 12 bar 40 µm
194840 LFRS-3/4-D-DI-MAXI-A G3/4 6800 l/min 0.5 ... 12 bar 40 µm
194792 LFRS-3/4-D-MAXI G3/4 9700 l/min 0.5 ... 12 bar 40 µm
194793 LFRS-3/4-D-MAXI-A G3/4 9700 l/min 0.5 ... 12 bar 40 µm
194823 LFRS-3/4-D-O-DI-MAXI G3/4 6800 l/min 0.5 ... 12 bar 40 µm
194841 LFRS-3/4-D-O-DI-MAXI-A G3/4 6800 l/min 0.5 ... 12 bar 40 µm
194794 LFRS-3/4-D-O-MAXI G3/4 9700 l/min 0.5 ... 12 bar 40 µm
194795 LFRS-3/4-D-O-MAXI-A G3/4 9700 l/min 0.5 ... 12 bar 40 µm
194830 LFRS-1-D-5M-DI-MAXI G1 6000 l/min 0.5 ... 12 bar 5 µm
194848 LFRS-1-D-5M-DI-MAXI-A G1 6000 l/min 0.5 ... 12 bar 5 µm
194812 LFRS-1-D-5M-MAXI G1 8000 l/min 0.5 ... 12 bar 5 µm
194814 LFRS-1-D-5M-MAXI-A G1 8000 l/min 0.5 ... 12 bar 5 µm
194831 LFRS-1-D-5M-O-DI-MAXI G1 6000 l/min 0.5 ... 12 bar 5 µm
194849 LFRS-1-D-5M-O-DI-MAXI-A G1 6000 l/min 0.5 ... 12 bar 5 µm
194813 LFRS-1-D-5M-O-MAXI G1 8000 l/min 0.5 ... 12 bar 5 µm
194815 LFRS-1-D-5M-O-MAXI-A G1 8000 l/min 0.5 ... 12 bar 5 µm
194832 LFRS-1-D-7-DI-MAXI G1 7800 l/min 0.5 ... 7 bar 40 µm
194850 LFRS-1-D-7-DI-MAXI-A G1 7800 l/min 0.5 ... 7 bar 40 µm
194808 LFRS-1-D-7-MAXI G1 11000 l/min 0.5 ... 7 bar 40 µm
194810 LFRS-1-D-7-MAXI-A G1 11000 l/min 0.5 ... 7 bar 40 µm
194833 LFRS-1-D-7-O-DI-MAXI G1 7800 l/min 0.5 ... 7 bar 40 µm
194851 LFRS-1-D-7-O-DI-MAXI-A G1 7800 l/min 0.5 ... 7 bar 40 µm
194809 LFRS-1-D-7-O-MAXI G1 11000 l/min 0.5 ... 7 bar 40 µm
194811 LFRS-1-D-7-O-MAXI-A G1 11000 l/min 0.5 ... 7 bar 40 µm
194828 LFRS-1-D-DI-MAXI G1 7000 l/min 0.5 ... 12 bar 40 µm
194846 LFRS-1-D-DI-MAXI-A G1 7000 l/min 0.5 ... 12 bar 40 µm
194804 LFRS-1-D-MAXI G1 10000 l/min 0.5 ... 12 bar 40 µm
194805 LFRS-1-D-MAXI-A G1 10000 l/min 0.5 ... 12 bar 40 µm
194829 LFRS-1-D-O-DI-MAXI G1 7000 l/min 0.5 ... 12 bar 40 µm
194847 LFRS-1-D-O-DI-MAXI-A G1 7000 l/min 0.5 ... 12 bar 40 µm
194806 LFRS-1-D-O-MAXI G1 10000 l/min 0.5 ... 12 bar 40 µm
德國(guó)FESTO減壓閥是通過(guò)調(diào)節(jié)，將進(jìn)口壓力減至某一需要的出口壓力,，并依靠介質(zhì)本身的能量,，使出口壓力自動(dòng)保持穩(wěn)定的閥門(mén)。從流體力學(xué)的觀(guān)點(diǎn)看,，減壓閥是一個(gè)局部阻力可以變化的節(jié)流元件,，即通過(guò)改變節(jié)流面積，使流速及流體的動(dòng)能改變,，造成不同的壓力損失,，從而達(dá)到減壓的目的。然后依靠控制與調(diào)節(jié)系統(tǒng)的調(diào)節(jié),，使閥后壓力的波動(dòng)與彈簧力相平衡,，使閥后壓力在一定的誤差范圍內(nèi)保持恒定。
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