Vacuum positive pressure

Helium leak detection Helium 10" 10" 7 10 7.10" Vacuum, positive pressure Yes... 

The BHS-Fest Filter. A different approach to the use of a dmm for pressure filtration is made in the BHS-Fest filter (Fig. 24). This permits a separate treatment of each filter section, in which the pressure may vary from vacuum to a positive pressure pressure regulation is much less difficult than in the conventional enclosed dmm-type pressure filter. 

The fluid dehvery in an air-spray system can be pressure or suction fed. In a pressure-fed system, the fluid is brought to the atomizer under positive pressure generated with an external pump, a gas pressure over the coating material in a tank, or an elevation head. In a suction system, the annular flow of air around the fluid tip generates sufficient vacuum to aspirate the coating material from a container through a fluid tube and into the air stream. In this case, the paint supply is normally located in a small cup attached to the spray device to keep the elevation differential and frictional pressure drop in the fluid-supply tube small. 

Dilute Phase Conveying. Dilute conveying systems, sometimes called disperse conveying or stream conveying, operate as positive pressure systems at pressures up to 100 kPa (14.5 psig), or as negative pressure systems (vacuum conveying) at pressures up to —50 kPa (—500 mbar). 

Rotary-Siphon Peeler Centrifuges In this type of centrifuge, a partial vacuum is drawn on the outer diameter or tne filter such that the filtrate flows through the cake under both centrifugal force as well as a positive pressure difference of about I atm or less. Thus, a higher rate of filtration takes place due to the increased driving force. 

The ejector is widely used as a vacuum pump, where it is staged when required to achieve deeper vacuum levels. If the motive fluid pressure is sufficiently high, the ejector can compress gas to a slightly positive pressure. Ejectors are used both as subsonic and supersonic devices. The design must incorporate the appropriate nozzle and diffuser compatible with the gas velocity. The ejector is one of the ( to liquid carryover in the suction gas. 

Equipment which can operate under a vacuum, either continuously or intermittently, must be designed to withstand vacuum conditions or otherwise be protected, in addition to any requirements for operation at positive pressure. Vacuum conditions must be specified. In some cases, this may include piping as well as vessels or other equipment. 

If it is extremely uneconomical to design at this point, then proper vacuum control must be installed. However, this is not the usual approach to the design. If the equipment can operate alternately under vacuum or positive pressure, it must be designed for the worst or controlling condition. 

These units are useful in both vacuum and pressure ranges and can usually develop compression ratios of 3 1 to 10 1, depending on the inlet absolute pressure. The units are positive displacement in performance. 

Compressors are available for vacuum as well as positive pressure service. Vacuums are obtained to 29 in. Hg abs and pressures up to 125 psig, with volumes of 2-25,000 cfm. 

Condensate from the low-pressure coil together with that from the flash vessel will then drain to a collecting tank, or direct to a condensate pump, for return to the boiler plant. If the pressure of the flash steam is left to find its own level it will often be sub-atmospheric. As the condensate must then drain by gravity through the steam traps these also must be sufficiently below the condensate drain points to provide an appropriate hydraulic head, and a vacuum breaker fitted above the coil. The alternatives are to allow the condensate to drain directly to a condensate pump, or to supply additional low-pressure steam through a pressure-reducing valve, to maintain a positive pressure in the coil and flash vessel. 

Figure 4-6 A combination vacuum-pressure system. A vacuum is used to withdraw material from a hopper car and positive pressure is used to transport it to storage silos.

Figure 4-4 shows a typical system under positive pressure. It differs from the vacuum system in that the material enters from one source and is distributed directly to several tanks. In this case no cyclone separator is used the air laden with solids enters the process bins directly. The decrease in velocity of the stream and its change in direction will cause most of the solids to drop out. For this system each receiver must have a filter to remove the remaining solids. Note that the blower is placed at the air entrance, instead of after the filter as in the vacuum system. Should a bag in the fiber filter break, no dust will get into the blower or its motor. Another advantage is that no contaminants from the atmosphere can enter the system when it is under positive pressure, except through the air inlet system. 

When a fluid other than air is used, the carrier gas usually must be recycled. Such a closed-loop system is shown in Figure 4-5. This can be operated wilh a vacuum or a positive pressure. 

Rotary valves have been specified for the receivers of the vacuum pneumatic conveying systems (RV-601 and RV-602) and for the feeders (RV-40 1) and receivers (RV-501) of the positive-pressure system transferring powder from the dryers to the extruders. Perry72 gives some recommended sizes for rotary valves. The power required by all these valves will probably not exceed 2 kw and will be ignored. 

After performing these tests with hydrogen and air mixtures at vacuum-level pressures, we posit the following as safety precautions when using hydrogen in a vacuum chamber. In addition, accordance to NFPA 86 section 12.3 and 12.4 is recommended. 

Hydraulic mobilization utilizes positive pressure or negative pressure (vacuum) as the force that transports the focused protein zones toward the detection point. During hydraulic mobilization, it is necessary to apply an electric field across the capillary in order to maintain focused protein zones.78 The main disadvantage of this type of mobilization is the parabolic shape of the hydrodynamic flow profile, which can decrease resolution. For this reason, only weak forces are used. 

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