Control Valve Split Range Example
As an example of a split-ranged system with opposite valve failure modes, consider the following temperature control system supplying either hot water or chilled water to a “jacket” surrounding a…
Control Valve Sequence Methods
In Control Valve Sequencing, for example, both control valves received the same pneumatic signal from a common I/P (current-to-pressure) converter. This means each valve received the exact same pressure signal…
Progressive Control Valve Sequence
Another form of control valve sequencing is used to expand the operating range of flow control for some fluid beyond that which a single control valve could muster. Once again…
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.
