Ejector position

An ejector provides a way to prevent contaminants from flowing through a fan. An ejector positions a fan so there is a vacuum upstream in the duct as the fan pushes air downstream without having a contaminant flow through the fan. An ejector design positions a fan so it is not in the vacuum flow that captures contaminants and blows air into the downstream flow. 

Typical runner sizes range fi-om 4mm to 7nun (0.157 to 0.276 in.) in diameter. Diameters above 7mm (0.276in) tend only to increase the cycle time and do not significantly assist in ihe filling of the mold. Runner lengths should be kept as short as possible and suitably sized ejectors positioned at runner junctions to ensure that the feed system is removed from the mold without difficulty. 

Compressors using the intermittent compression mode are referred to as positive displacement compressors, of which there are two distinct types reciprocating and rotary. Continuous-mode compressors are also characterized by two fundamental types dynamic and ejector. 

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. 

A further source of stress may arise from incorrect mould design. For example, if the ejector pins are designed in such a way to cause distortion of the mouldings, internal stresses may develop. This will happen if the mould is distorted while the centre is still molten, but cooling, since some molecules will freeze in the distorted position. On recovery by the moulding of its natural shape these molecules will be under stress. 

A useful summary of the typical equipment used for developing and maintaining process system vacuum is presented in Table 6-1. Also see Birgenheier [33]. The positive displacement type vacuum pumps can handle an overload in capacity and still maintain essentially the same pressure (vacuum), while the ejectors are much more limited in this performance and cannot maintain the vacuum. The liquid ring unit is more like the positive displacement pump, but it does develop increased suction pressure (higher vacuum) when the inlet load is increased at tlie lower end of the pressure performance curve. The shapes of these performance curves is important in evaluating the system flexibility. See later discussion. 

Steam jet thermocompressors or steam boosters are used to boost or raise the pressure of low pressure steam to a pressure intermediate bettveen this and the pressure of the motive high pressure steam. These are useful and economical when the steam balance allows the use of the necessary pressure levels. The reuse of exhaust steam from turbines is frequently encountered. The principle of operation is the same as for other ejectors. The position of the nozzle with respect to the diffuser is critical, and care must be used to properly posidon all gaskets, etc. The thermal efficiency is high as the only heat loss is due to radiation [5]. 

Positive displacement pumps are self-priming by their normal operating action and are designed to cope with mnning dry. Centrifugal pumps are not inherently selfpriming, and need to be provided with assistance in the form of ejectors, as in Figure 32.56 or dry vacuum pump systems. In these systems, a dry vacuum pump allows air to be drawn out and where an automatic valve prevents... 

Return ejector pins to retraced position as mold closes for next cycle... 

Other pieces may have to be elevated to enable the system to operate. A steam jet ejector with an intercondenser that is used to produce a vacuum must be located above a 34 ft (10 m) barometric leg. Condensate receivers and holding tanks frequently must be located high enough to provide an adequate net positive suction head (NPSH) for the pump below. For many pumps an NPSH of at least 14 ft (4.2 m) H2O is desirable. Others can operate when the NPSH is only 6 ft (2 m) H2O. See Chapter 8 for a method of calculating NPSH. 

The powder is supplied to the gun by a powder pump at a uniform and consisfent rate. There are two types of powder pumps ejector type, using the venturi principle, and auger pumps, which use positive displacement. A corona charging system is most widely used to electrostatically charge the powder. The electrostatic spray gun has several functions ... 

Check correct function of weighing, package length check, sloping position check, and package ejector, as well as correct range of tolerance. Time interval before daily production start every 2 h during production... 

Figure 3.13. Crude oil vacuum tower. Pumparound reflux is provided at three lower positions as well as at the top, with the object of optimizing the diameter of the tower. Cooling of the side streams is part of the heat recovery system of the entire crude oil distillation plant. The cooling water and the steam for stripping and to the vacuum ejector are on hand control.

By and large, ejectors and motionless mixers have similar mass transfer performance at a given gas-to-liquid flow ratio and energy input. However, ejectors have a number of benefits and drawbacks compared to a motionless mixer. On the positive side, the ejector suction means that a pressurized gas supply is not required. The unrestricted mixing tube means that solid formation due to reaction is not problematic. Against this, the operation is sensitive to changes in the gas-liquid flow ratio and diameter/length ratio. Gas-to-liquid flow ratios are also more limited in ejectors. 

The most commonly used vacuum pumps are steam-jet ejectors and several positive-displacement pumps, which are shown in Figures 5.1 and 5.2. Some of the characteristics of vacuum pumps are given in Table 5.1. A prime consideration when selecting a vacuum pump is the compatihility of a gas with a seal fluid. To avoid these problems, there is a trend toward using dry pumps where a seal fluid or lubricant is not used [60]. 

To operate the Opus analyzer, the operator selects a test and provides other information through an interactive touch screen/LCD display. When prompted, the operator inserts one assay-specific test module per test into the loading port of the instrument. The loader transports the test module to a 20 position incubated rotor where the test module is equilibrated to 37 C. The analyzer prompts for sample cup and pipette tip trays. Once these trays are supplied, the analyzer automatically picks up a new pipette tip, aspirates the sample and dispenses the sample onto the test module. For certain assays the pipettor also transports conjugate, substrate or other reagents from the test module wells to the test module dispense port. After processing, the test module is rotated to the read position where the fluorimeter takes measurements. The rotor then moves the used test module to the loader/ ejector where it is... 

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