Avalveisadevicethatregulates,directsorcontrolstheflowofafluid(gases,steam,liquids,fluidizedsolids,orslurries)byopening,closing,orpartiallyobstructingvariouspassageways.Valvesaretechnicallyfittings,butareusuallydiscussedasaseparatecategory.Inanopenvalve,fluidflowsinadirectionfromhigherpressuretolowerpressure.Thesechangesmayactuponadiaphragmorapistonwhichinturnactivatesthevalve.Theycanbeelectromechanicalactuatorssuchasanelectricmotoror