In this manner, {HEAD ~ the skirt valve} can be much more rigid than an umbrella valve to keep the valve closed when not in use and prevent back pressure in the drain pipe from opening the valve, while {TAIL ~ the ends} of the skirt valve are flexible to allow for fluid flow 
In this manner , { HEAD ~ the skirt valve } can be much more rigid than an umbrella valve to keep the valve closed when not in use and prevent back pressure in the drain pipe from opening the valve , while { TAIL ~ the ends } of the skirt valve are flexible to allow for fluid flow
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH