Ivalvu yokunceda, eyaziwa ngokuba yivalvu yokunciphisa uxinzelelo (i-PRV), luhlobo lwevalvu yokhuseleko esetyenziselwa ukulawula okanye ukunciphisa uxinzelelo kwinkqubo. Ukuba uxinzelelo belungalawulwa, lunokwakheka kwaye lubangele ukuphazamiseka kwenkqubo, ukusilela kwesixhobo okanye isixhobo, okanye umlilo. Ngokuvumela ulwelo oluxinzelelweyo ukuba luphume kwinkqubo ngendlela encedisayo, uxinzelelo luyancitshiswa. Ukuthintela imithambo yoxinzelelo kunye nezinye izixhobo ukuba zingabi phantsi koxinzelelo oludlula imida yazo yoyilo,ivalvu yokuncedayakhiwe okanye icwangciswe ukuba ivuleke ngoxinzelelo olumiselweyo.

Iivalvu yokuncedaiba “yindlela engenakuphikiswa” xa uxinzelelo olubekiweyo lugqithwe kuba ivalvu inyanzeliswa ukuba ivuleke kwaye olunye ulwelo luthunyelwa kwitshaneli encedisayo. Umxube wolwelo, igesi, okanye ulwelo-gesi olujikeleziswa kwiinkqubo ezinezilwelo ezinokutsha uyabuyiselwa okanye uphume umoya.

[1] nokuba ithunyelwa ngenkqubo yemibhobho eyaziwa ngokuba yi-flare header okanye i-relief header ukuya kwi-gas flare ephakathi, ephakamileyo apho itshiswa khona, ikhupha iigesi ezivuthayo ezingenanto emoyeni, okanye ngenkqubo yokubuyisela umphunga ohamba ngamandla oxinzelelo oluphantsi.

[2] Kwiinkqubo ezingenabungozi, ulwelo luhlala lukhutshwa emoyeni ngepayipi efanelekileyo yokukhupha amanzi ebekwe ngokukhuselekileyo ebantwini kwaye yakhelwe ukuthintela ukungena kwemvula, nto leyo enokuchaphazela uxinzelelo lokuphakamisa olubekiweyo. Uxinzelelo luya kuyeka ukwakheka ngaphakathi kwinqanawa njengoko ulwelo luthunyelwa kwenye indawo. Ivalvu iya kuvala xa uxinzelelo lufikelela kuxinzelelo lokubuyisela indawo yokuhlala. Ubungakanani boxinzelelo ekufuneka luncitshiswe ngaphambi kokuba ivalvu ihlale kwakhona lwaziwa ngokuba yi-blowdown, edla ngokubonakaliswa njengepesenti yoxinzelelo olubekiweyo. Ezinye iivalvu zine-blowdowns ezihlengahlengiswayo, kwaye i-blowdown inokutshintsha phakathi kwe-2% kunye ne-20%.

Kucetyiswa ukuba indawo yokuphuma kwevalvu yokunceda kwiinkqubo zegesi ezinoxinzelelo oluphezulu ibe kwindawo evulekileyo. Ukuvulwa kwevalvu yokunceda kuya kubangela ukwakheka koxinzelelo kwinkqubo yemibhobho esezantsi kwevalvu yokunceda kwiinkqubo apho indawo yokuphuma iqhagamshelwe khona kwimibhobho. Oku kuthetha ukuba xa uxinzelelo olufunekayo lufikelelwe, ivalvu yokunceda ayizukuphinda ihlale. Iivalvu zokunceda ezibizwa ngokuba “zii-differential” zihlala zisetyenziswa kwezi nkqubo. Oku kubonisa ukuba uxinzelelo lusebenza kuphela kwindawo encinci kakhulu kunokuvulwa kwevalvu.

Uxinzelelo lwe-outlet yevalvu lungayigcina ivalvu ivulekile ukuba ivalvu ivuliwe kuba uxinzelelo kufuneka lwehle kakhulu ngaphambi kokuba ivalvu ivale. Njengoko uxinzelelo olukwinkqubo yepayipi yokukhupha umoya lunyuka, ezinye iivalvu zokunceda eziqhagamshelwe kwinkqubo yepayipi yokukhupha umoya zinokuvuleka. Le yinto ekufuneka uyikhumbule. Oku kunokubangela ukuziphatha okungathandekiyo.