Two port valve-
In globe valves, the flow of the fluid through valve follows an S-path. Due to this, the flow direction changes twice which results in higher pressure drops.
The differential pressure upon which the valve operates depend upon the size of valve and the actuator.
The power required for actuator is given by
Power = Area of the valve plug X Differential pressure
Bellows are also used for high capacities or higher differential pressure.
Double seat-two port valve:
The valve consists of a common spindle consisting of two valve plugs and two valve seats. Forces are balanced on the top and lower plugs
Three way valve-
A three way valve is a constant flow rate valve used for either mixing or diverting application. In these valves, the total flow rate remains constant. In application where three way valve are employed, the liquid circuit will naturally split into two separate loops, constant and variable flowrate.
A undersized three way valve will create unnecessary differential pressure across the ports. It may result in increased pumping cost and short steam travel will have large impact on fluid directed through load changes.
For three way mixing valve, all the ports have to be in equilibrium. The thrust force produced due to flow through each port is countered by the thrust force due to flow through another port. Hence only frictional forces and sealing forces need to be considered while sizing the actuator. The shut off pressure do not play any role in actuator selection.
Dividing Flow:
The flow AB is divided into two exit flows A and B.
The direction of the flow is always against the plug, the water hammer caused thereby can be avoided. Standard diaphragm actuators can be used without special devices as for instance hydraulic brake. The plugs are guided in the upper and lower seat.
Port AB = Port A/ Port B
Mixing Flow:
The entrance flows A and B are mixed to a single exit flow AB. Typical application is temperature control.
Port A/ Port B = Port AB
Both types, mixing and dividing, are built from the same parts of the modular parts system. The plugs for mixing and dividing are identical. With some additional parts like spindle, distance bushing, one type can be converted to other. The seat remains unchanged.
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