Exclusive Control Valve Sequence
Other applications for split-ranged control valves call for a form of valve sequencing where both valves are fully closed at a 50% controller output signal, with one valve opening fully…
Complementary Control Valve Sequence
The first type of control valve sequencing is a mode where two valves serve to proportion a mixture of two fluid streams, such as this example where base and pigment…
Control Valve Positioners
The reason why a pneumatic control valve’s stem position corresponds linearly to the amount of air pressure applied to the actuator is because mechanical springs tend to follow Hooke’s Law,…
Valve Seat Leakage Test
In some process applications, it is important that the control valve be able to completely stop fluid flow when placed in the “closed” position. Although this may seem to be…
Bellows Seal Valve Working Principle
A completely different approach to packing is a device called a bellows seal : an accordion-like metal tube fastened to the valve stem and to the bonnet, forming a leak-proof…
What is Valve Packing ?
Regardless of valve type, all stem-actuated control valves require some form of seal allowing motion of the stem from some external device (an actuator ) while sealing process fluid so…
Laminar Flow Meter Working Principle
A unique form of differential pressure-based flow measurement deserves its own section in this flow measurement chapter, and that is laminar flow meter.
RTD Calibration
R.T.D. Accuracy checks for a resistance temperature detector/device (RTD) is often necessary to validate the accuracy of a new RTD. How They Work There are three basic types of RTDs:…
Thermocouple Calibration
Thermocouples Thermocouples measure temperature and are used quite often in process controls. How They Work When wires of two different thermoelectrically homogeneous materials are joined at one end and placed…
DP Transmitter Dry Leg & Wet Leg Calculations
In any process industry, level measurement is very important for safety and process purpose. The level can be measured by two methods. Direct method Indirect method Here we discuss the…
