Speaking of the single core,when the medium is flows, the valve stability is good;when the medium is flows the close mold,the valve stability is bad.The double-seat valve has two valve cores,gets down the valve core to be in the class to shut,on the valve core is in flows,like this, when small opening work,flows the close mold the valve core on easily to cause the valve vibration,this is the double-seat valve cannot use in the small opening work the reason being at.