High-pressure pinch valve

Figure 18. High-pressure pinch valve (Larox Pty Ltd).

Figure 3.16 Schematic representation of (A) NCE with negative pressure pinched sample injection. SP, syringe pump V, 3-way valve, HV, high voltage power supply. (B) View of the connection from the three-way valve to the sample waste reservoir SW [106].

The most widely used control valves for liquid and high pressure gas streams are the various sliding stem valves such as the bevel plug, V-port, parabolic plug, and for small flows the needle valve. For corrosive materials and slurries, pinch-type valves like the Saunders patent valves are used. Rotary stem valves include plug types and for gas flows butterfly valves, dampers, and louvers. 

Steam is flow controlled, with the flow controller setpoint coming from a temperature controller that controls a tray temperature in the stripping section of the column. Low, base level or high column pressure pinches the steam valve. 

Vent line valves This is a deceptively easy duty, butif it is on ahigh pressure blow tank handling fly ash or cement, the valve will have to operate in a very harsh environment. The air velocity will be very high, albeit for a very short period of time, but a lot of abrasive dust is likely to be carried with the air. If the material is abrasive then the choice is between a pinch valve and a dome valve. If the material is non-abrasive, a diaphragm valve could be used. 

If the pressure in the stripper gets too high, an override controller pinches both valves V9 and V3. 

High wet gas compressor suction pressure. An increase in the pressure at the suction to the wet gas compressor backs up through the fractionator overhead condensers and trays, the vapor line, and the reactor cyclones to the riser. Now, for the operator to maintain a proper regenerator slide valve AP (i.e., at least 3 psi), he must pinch back on the flue gas slide valve to raise the regenerator pressure. This, of course, translates directly into an increase in air-blower discharge pressure. 

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