Insufficient Vacuum

Obstruction in vapor system. This causes excessive pressure drop. The obstruction is usually a deposit in the noncondensible take off nozzle of the condenser. The obstruction must be removed to correct the problem. 

Air leaks in system. This results in overloading the vacuum system because of excess noncondensibles and water of saturation in noncondensible stream. Air leakage must be stopped to correct the problem. 

Excessive backpressure on vacuum system. This is caused by an obstruction in the noncondensible discharge pipe or the discharge pipe sealed too deeply in the hot well. The obstruction must be removed or the depth of the seal in the hot well reduced to correct the problem. 

Low steam pressure. This applies to steam ejectors only. The cause is low line pressure, wet steam or blockage in the steam line. This reduces the driving force ofthe ejector and reduces its air handling capacity. By removing the cause of the low steam pressure, the problem of insufficient vacuum is corrected. 

Low seal water flow. This applies to mechanical vacuum pumps only. This reduces the subcooling of the noncondensible, increasing the loading to the system. 

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The vacuum in the CST main chamber was insufficient. This was partially alleviated by tightening down the gland seals on either end of the main chamber auger. However, insufficient vacuum levels in the main chamber were a chronic problem during all CST testing and would have to be addressed in any final design. 

In Example 2.12, the method of random balance, factors have been selected by the effects of their significance on dynamic viscosity of uncured composite rocket propellant. The screened-out factors are X3 mixing speed X5 time after addition of AP and Xg vacuum in vertical planetary mixer. Since insufficient vacuum in a mixer causes bubbles to appear in the cured propellant, the value of this factor is fixed at the most convenient one. For the other two factors a design of basic experiment has been done according to a FUFE matrix, as shown in Table 2.103, and aimed at obtaining the mathematical model of viscosity change. 

Insufficient vacuum see Section 2.2/obstruction in vapor system/insuffident cooling water to condenser/temperature of the cooling water to the condensers > design/air leaks. For steam ejectors steam pressure < design. For mechanical vacuum pumps seal water flowrate < design/rpm < design. 

Blisters Insufficient vacuum Excessive moisture Gases entrapped Water inside pipe Increase vacuum Maintain normal of moisture in compound Reduce temperature Stop water access... 

Insufficient vacuum flow leads to hole wall quality problems such as gouging, nail heading, and excessive smearing. Table 25.1 provides a hole-quaUty troubleshooting matrix that addresses these problems. The minimum industry standard for vacuum strength is approximately 20 in. of water measured at the pressure foot. 

Insufficient vacuum reserve to permit one full brake application after engine is shut off. (393.50(b))... 

Inaccurate beam intensity determinations may result from the anission of secondary electrons or from an insufficient vacuum ... 

In terms of analytical performances, the consequences of an insufficient vacuum are numerous and disastrous. All analyzers use a field (e.g., electromagnetic or magnetic) to separate ions according to their mass-to-charge ratios. The trajectory of the ions in the field must be as precise as possible. If the ions collide with residual molecules, they can react with them, deviate from their trajectory, and be fragmented by the collisions. These phenomena will result in resolution, sensitivity, and spectral reproducibility problems. Furthermore, residual molecules are susceptible to being ionized. The resultant ions will interfere with the characteristic ions of the analytes within the mass spectra. 

Capillary Suction Processes. The force needed to remove water from capillaries increases proportionately with a decrease in capillary radius, exceeding 1400 kPa (200 psi) in a 1-p.m-diameter capillary. Some attempts have been made to use this force as a way to dewater sludges and cakes by providing smaller dry capillaries to suck up the water (27). Sectors of a vacuum filter have been made of microporous ceramic, which conducts the moisture from the cake into the sector and removes the water on the inside by vacuum. Pore size is sufficiently small that the difference in pressure during vacuum is insufficient to displace water from the sector material, thus allowing a smaller vacuum pump to be effective (126). 

The actual liquid-to-gas ratio (solvent-circulation rate) normally will be greater than the minimum by as much as 25 to 100 percent and may be arrived at by economic considerations as well as by judgment and experience. For example, in some packed-tower applications involving veiy soluble gases or vacuum operation, the minimum quantity of solvent needed to dissolve the solute may be insufficient to keep the packing surface thoroughly wet, leading to poor distribution of the liquid stream. 

Figure 8.16. Schematic diagram of modulus versus temperature for two materials A and B to be shaped in the rubbery phase in the temperature range T]-T2. In this range the modulus of A is above a critical figure C above which atmospheric pressure is insufficient to shape sheet of a given thickness. Such material could therefore not be vacuum formed. The type B material would, however, present no problem on this score...

Vacuum bag bonding is restricted by definition to less than 1 atm (<15 psi) which can be insufficient to achieve good part contact and prevent bondline voids. Hence vacuum bag bonding is rarely used outside of repair situations. 

When gravity is insufficient to induce flow, the pressure of the atmosphere is allowed to act on one side of the filtering medium, while a negative or suction pressure is applied on the discharge side. This type of filtering device is referred to as a vacuum filter. The application of vacuum filters is typically limited to 15 psi pressure, although there are applications where this value can be exceeded. Note... 

When available land space is insufficient for land farming, soil treatment can be carried out in piles or pits. Typical biopile and biopit constructions are presented in Figure 14.8 and Figure 14.9, respectively. When the soil has relatively low permeability, the pile can be constructed with sequential lifts of soil, approximately 60 cm in thickness, separated by permeable sand layers. These layers are connected with a vacuum pump or blower that is used to produce airflow though the soil pile. Water and nutrients are sprinkled on the top of the pile. 

The appearance of air bubbles in the polymer melt may occur under certain circumstances during processing. This phenomenon is rarely related to obvious faults in the polymer, but sometimes gas bubbles can be observed in cases of decreased thermal stability. Gas bubbles appear due to a certain amount of dispersed gas in the polymer matrix. Insufficient removal of gas from the extruder, particularly from the compression zone, can also cause the problem of air bubbles in the melt. An influence of the extruder screw could be established, because gas bubbles can be removed to some extent by using special screws or changing the extrusion conditions, along with the application of a vacuum. 

The fractions coilected are each run dropwise into 100 ml of stirred methanol to which two drops of concentrated hydrochloric acid have been added.Turbidity or precipitation will be observed from about the 6th fraction to about the 20th fraction.The precipitated fractions are filtered off, washed with methanol and dried to constant weight in vacuum at 20 °C. For each fraction the viscosity is measured in water at 25 °C using a capillary viscometer (capillary diameter 0.35 mm) and at as high a concentration as possible (10 g/l) in order to minimize errors.The limiting viscosity number, and hence the molecular weight, is estimated (see Sect. 2.3.3.3.1). Adjacent fractions for which there may be insufficient material for a viscosity measurement,can be combined where necessary. 

Many early chemists observed that when ordinary white phosphorus was exposed to light, even in a vacuum, it became red. Although the great Swedish chemist J. J. Berzelius regarded the red substance as a modification of phosphorus, others believed that an oxide had been formed by interaction of the insufficiently dried phosphorus with water. Anton von Schrotter isolated the red substance, made a thorough study... 

When the final juice product is a concentrate, the clear filtered or cleaned cloudy juices are automatically subjected to heat treatment during the course of their concentration. (Figure 3.7 provides on overview of the concentration process.) Heat treatment of juices is an area where the design of process requires careful consideration in order to avoid any detrimental effects on flavour and appearance of the product. Early evaporators had demonstrated that high-vacuum-low-temperature processing produced concentrate of good flavour quality, but it was soon discovered that there was a drawback in that the heat treatment was insufficient to deactivate pectin methylesterase, which gave rise... 

In practice, clean (very clean ) cleaved or otherwise smoothed metal surfaces should be made to effect a firm mechanical contact using a strong force but one that is still insufficient to cause macroscopic deformation even at an elevated temperature. This will have to be been done, usually, in vacuum or at least in an inert atmosphere. The problems of hard to get to (inaccessible) joints and possibly objectionable thermal conditions and the resultant undesired microstructures such as Kirkendall voids, for instance, are minimized, if not eliminated all together. Thus, good-quality, distortion-free joints requiring no additional machining or other posttreatment can be achieved. 

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