Analyzers

DOE-HDBK-1132-99

4.7

Analyzers.

When selecting analyzers, sample characteristics including quantity and type of

chemical components should be considered carefully.

To prevent sample contamination, avoid sharing of sample lines between

different analyzers.

Where available, use of automatic calibration feature is desirable to counter drift

in analyzer performance.

Proper sampling conditioning is important for satisfactory operation of an

analyzer.

4.8

Solenoid Valves . Two methods are usually employed to operate solenoid valves:

direct and pilot-operated. Direct operators are those in which the force of the coil core

directly opens or closes the valve. The force required to operate the valve is directly

proportional to the valve's orifice and line pressure. As the size and line pressure

increases, the size of the coil and core increases accordingly. To avoid this limitation,

pilot-operated solenoid valves may be used.

The use of pilot-operated solenoid valves is limited in two ways: by the maximum

differential pressure and by the minimum amount of differential pressure required to

operate the valve. Operational failure may result if either is ignored in the application.

For example, three-way solenoid valves are often used to direct an air supply to, or

exhaust the air from, a pneumatic valve operator. If valve position is critical, two

solenoid valves in the air supply line should be considered, especially when priority

interlocks are necessary. Proper function may not occur if the solenoid valve's minimum

required differential pressure is ignored. In critical cases, the application should be

tested for the various operating modes and the solenoid valve manufacturer consulted

regarding the product's capabilities.

II-48