Open bleed/vent valve

The open bleed/vent valve represents a low-pressure spot in the system. Therefore, if there is a release through the closed block valve, the hazardous materials will bleed off before entering the equipment being worked on. If the discharge from the bleed/vent line could itself be hazardous, it can be routed to a safe location, such as a flare header. 

Injection with elimination of solvent the sample is introduced into the cold injector after which the vent valve is opened. Vent flow rate is very high and can attain 1000 mL/min to eliminate all of the solvent. The injector is then heated to permit transfer of the less volatiles compounds onto the column, the bleed valve now being closed (splitless mode). In this way it is possible to inject up to 50p,L in a single injection or up to 500 p,L of sample solution, over several injections. This method eliminates the step of the preliminary concentration of sample prior to injection. 

Development of low and high pressure is a possibility and this may cause malfunction of burner operation. In general, a low-pressme switch (PSL) is installed upstream of the first shutdown valve, and a high-pressure switch (PSH) is installed downstream of the second shutdown valve, hi case of low and high pressures, the signal will close all shutdown valves on the main gas line, as well as the shutdown valve on the pilot gas line, hi most cases, a combination of shutdown and venting is installed together. This operates as a double block and bleed maimer, and under shutdown situations, the vent valve opens and releases the gas trapped within the double-block shutdown valves. 

The kiln operator selects the appropriate sehedule and adjusts the temperature and humidity as necessary by manipulation of the heating eoils (dry heat) and spray valves (steam), with occasional adjustments to the air inlet and outlet vents, which exchange hot, moist air from the kiln for cold, drier air from outside. The steam line raises and maintains the humidity while the kiln warms up. It should be used only infrequently thereafter as economy in operation depends on making maximum use of the moisture extracted from the lumber to maintain the required humidity in the kiln. As moisture evaporates the humidity rises above the schedule value and the vents open a little to bleed off some of the hot damp air. 

A three-valve configuration common in shut-off applications to prevent release of a gas or fluid to the area of isolation by providing a positive means of isolation. Two main shut-off valves (block valves) operate on the main process line to stop flow. A third bleed valve in a T-section between the two block valves fitted with a vent or drain can be opened to relieve pressure of the process fluid from the region between the two block valves. In this fashion, passing of the isolation valve on the active side will not allow entry into the isolated equipment. Typically considered as a one out of... 

From equation (17.6) we can see that open-loop pressure dynamics are essentially first order. Since in most cases the inert gas bleed and the vent flow are fiiirly small, the valve gains, SwjgIBBc and dwJdBc, tend to be small. Together with the first-order dynamics, this commonly leads to large controller gains (small proporticmal bands) and control valve saturation fcM" fairly small disturbances. 

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