VALVE CHARACTERISTICS

8.5 VALVE CHARACTERISTICS Factors that determines the choice of valve type Corrosion resistance Operating temperature ranges High and low pressures Velocities Pipe size Fluids containing solids Correct valve installation is necessary and vendor recommendations must be followed so that sludge can be trapped upstream of a valve. To minimize disturbances and have good flow , clear run from 1 to 5 pipe diameters of upstream & downstream should be allowed. Capacity number (Cv) , indicates no. of gallon per minute at 60F (15.5C) & pressure drop 1 psi (6.9 kPa). Relation between Pd(psi),flow rate Q ,CV and SG is Cv = Q d)

8.6 VALVE FAIL SAFE Position of a actuators is considered as there is (a loss of power when system shutdown occurs or fuel continues flow to heaters). Globe valve design that operate pneumatically or hydraulically to open & close when system is failure. Failure mode is detect by changing the spring position & pressure port. The closing of globe valve occurs when pressure applied to pressure port to oppose spring action. Spring action on piston to force valve to its position when system fails or there is loss of pneumatic pressure. When spring is removed to above the piston, inlet & exhaust ports are reversed, pressure that aplied will work against spring action to open the valve.

When the pressure loss control and system fails ,spring force to piston down &close the valve . Hydraulically, electrically, two & three way operated valves also available that operates when system fails.8.7 ACTUATORS They are used to control various type of valves . Two types of pneumatic actuators are 1)Reverse action when lifting the valve against the pressure of valve.2)Direct action when moving the valve down against the pressure of valve.

Depends on valve the pressure can occurs on closing or opening.

Actuators must operate valve against the pressure acting on valve and able to close tightly the valve.THANK YOU