Backpressure control valve

Option 2 A backpressure control valve - direct acting is not required... 

Suppose we increase the pressure by partly closing the backpressure control valve. This will quickly increase the pressure in the drum from 10 to 15 psig. The pressure at the suction of the pump will also increase, from 15 to 20 psig. However, will this provide more NPSH to the pump ... 

Answer suddenly increase the pressure in the drum, by partly closing the backpressure-control valve shown in Fig. 25.4. This will instantly increase the pressure at the suction of the pump. It is true, as we said before, that raising the pressure in a drum does not increase the available NPSH, assuming that the vapor and liquid are at equilibrium. The idea of equilibrium assumes that the vapor is at its dew point and the liquid is at its bubble point. 

Let us refer again to Fig. 28.1. Suddenly, there is an increase in the molecular weight of the wet gas. This causes the density of the gas to increase. This results in an increase of the compressor AP. As the compressor AP increases, the compressor s suction pressure decreases. Why Well, if the discharge pressure is kept constant by the absorber backpressure control valve, then a bigger AP must drag down the suction pressure. The reduced suction pressure increases the suction vol-... 

Figure 4.6-4 Scheme of a continuously operated device for high-pressure ethene (co)polymerizations Ex, exhaust RD, rupture disk BPV, backpressure control valve. 

Continuous Pressure Filters These filters consist of conventional drum or disk filters totally enclosed in pressure vessels. Filtration takes place with the vessel pressurized up to 6 bar and the filtrate discharging either at atmospheric pressure or into a receiver maintained at a suitable backpressure. Cake discharge is facilitated through a dual valve and lock-hopper arrangement in order to maintain vessel pressure. Alternatively, the discharged filter cake can be reslurried within the filter or in an adjoining pressure vessel and removed through a control valve. 

In most units, about two-thirds of the flue gas pressure is let down via an orifice chamber or across an orifice chamber. The orifice chamber is a vessel containing a series of perforated plates designed to maintain a given backpressure upstream of the regenerator pressure control valve. 

Condensate pumps are sometimes used to overcome such backpressure problems. However, these pumps are often not kept in good repair, and condensate is still lost to the sewer. Eliminating the steam inlet control valve of the type shown in Fig. 8.4 has helped recover condensate from many reboilers, supplied with low-pressure steam. 

This is where the permeate backpressure per stage is entered. Clicking on the control valve will open up a box into which the backpressure is entered. Minimum and maximum backpressures are given as guides. 

The barometric leg represents one way to prevent process material from flowing back into the vaporizer. The height of the leg should suit the density of the process fluid. When the process operates under pressure or when chlorine enters the process against a substantial head of process fluid, a barometric leg may be impractical. Other devices used include low-pressure shutdown systems, power-operated control valves, backpressure regulators, and vacuum breakers. Check valves are another possibility, but they are not widely recommended and must be used with discretion and with some assurance that they provide positive shutoff. A variation is the use of an automatic value that shuts when the differential pressure between two points in the transfer line reverses, indicating the potential for backflow. 

Control backpressure on the POD LLO and HLO streams by adjusting valves Vila and Vllb, respectively. 

Figure 7.2.4 Experimental set-up used for SFC-NMR experiments (a) modifier pump (b) SFC pump (c) CO2 cylinder with dip-tube (d) cryostat (e) GC oven with mixing chamber and separation column (f) injection valve (g) UV detector (h) NMR magnet (i) backpressure regulator or restrictor (j) hardware control unit...

Another method for controlling both backsiphonage and backpressure is a single check valve (Fig. 4). In theory, a check valve should provide adequate protection. It is, however, entirely dependent on the leakproof integrity of its seals and, as such, is not acceptable for use in situations where backflow into potable-water supplies could include hazardous, noxious or otherwise undesirable materials. 

Figure 5.2.1. Simplified diagram of a Py-GC system (not to scale). The pyrolyser is schematized as a heated filament type. A piece of a deactivated fused silica line is passed through the injection port of the GC and goes directly into the pyrolyser. This piece of fused silica is connected to the column, which is put in the GC oven. The pneumatic system consists of (1) a mass flow controller, (2) an electronic flow sensor, (3) a solenoid valve, (4) a backpressure regulator, (5) a pressure gauge, and (6) septum purge controller. The connection (7) is closed when working in Py-GC mode, and connection (8) is open. (Connection (7) is open when the system works as a GC only.) Connection (9) is closed and connection (10) is open when the GC works in splitless mode (purge off). Connection (10) is closed and connection (9) is open when the GC works in split mode (purge on). No details on the GC oven or on the detector are given.

Membrane Flux Performance for the Hollow Fiber Units. Figures 3a and 3b show the results of a cell separation pilot scale run in which transmembrane pressure was maintained constant at 4.0 psi and linear velocity through the fibers was maintained at 1.0 m/sec (100 1pm). Transmembrane pressure was controlled with a backpressure valve on the combined permeates from the hollow fibers. Note that the flux vs. concentration curve for this run does not conform to theoretical predictions for concentration polarization (see Figure 3b). Flux on this semi-log plot does not decline linearly, but, rather, shows two phases of fouling. The initial phase (approximately 20 minutes in duration) is characterized by a rapid loss in flux, while the second stage (approximately 90 minutes in duration) is more gradual. The initially rapid decline caused an unacceptably low average flux of 10 l/m -hr. 

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