Pressurization leakage compensation

Pressurization techniques are similar to those used in zones 1 and 2, with the exception that purging shall not be applied. The high flow rate of protective gas during the purging period accompanied by a high velocity of gas may stir up dust layers inside the p-room on components and thus adversely affect the safety of this type of protection. Static pressurization, leakage compensation... 

Figure 6.13 Same as Fig. 6.11, pressurization with leakage compensation, enclosures without moving parts. 

In case of leakage compensation, there is a strong tendency to achieve zero leakage for economical reasons. But very low leakage enclosures (and without a heat exchanger to remove internal thermal losses) tend to exceed the maximum pressure differential, e.g. of 300 Pa (=3.0mbar) during operation under load. 

With inert gas as protective gas and an oxygen content inside the containment system = 2% (v/v), the flow rate of protective gas after the purging phase may be reduced to that necessary for maintaining the minimum pressure differential (this may be considered as a shift towards leakage compensation )... 

In some hydraulic systems, it is necessary to maintain the system pressure within a specific pressure range for long periods. It is very difficult to maintain a closed system without some leakage, either external or internal. Even a small leak can cause a decrease in pressure. By using an accumulator, leakage can be compensated for and the system pressure can be maintained within acceptable range for extended periods. Accumulators also compensate for thermal expansion and contraction of the liquid due to variations in temperature or generated heat. 

In plain bearings, the lubricating fluid must be replenished to compensate for end leakage in order to maintain their load-carrying capacity. Pressure lubrication from a pump-or gravity-fed tank, or automatic lubricating devices such... 

Small capacity pumps commonly referred to as "jockey" pumps are provided on a firewater system to compensate for small leakages and incidental usage without the main pump(s) startup. They are set to start 0.70 to 1.05 kg/sq. cm. (10 to 15 psi) above the start up pressure of main firewater pumps. In some cases a cross-over from the utility water system can be used in place of a jockey pump, however a check valve is installed to prevent drain down of the firewater by the utility water system. Jockey pumps do not require the... 

Rotor Thrust Problems Thrust loads in compressors due to aerodynamic forces are affected by impeller geometry, by pressure rise through the compressor, and by internal leakage due to labyrinth clearances. The impeller thrust is calculated by using correction factors to account for internal leakage, and a balance piston size is selected to compensate for the impeller thrust load. The common assumptions made in the calculation are... 

In the gas room of the manometric drill hole, the two ends of the sealed hole bear the same amount of pressure when the gas pressure achieves balance. According to the law of mass conservation, when the gas pressure in the manometric drill hole reaches balance, the amount of compensate gas in the gas room is approximately equal to the amount of axial leakage of the sealed section. As is shown in the following formula ... 

Chapter 4 discusses the many circumstances in which health and safety problems do not generate compensation costs and where employers thus have no economic incentive to attend to OHS. For example, occupational illnesses with long onset times, such as cancer, tend not to give rise to compensation claims and so impose no financial pressure on employers. Again, dangerous occurrences, such as gas leakages, may not in fact injure anyone, but if not responded to appropriately have the potential to cause death on some future occasion. Such problems require resolute action by the regulatory authorities in order to protect worker health and safety. 

Very important for a valve is, that in a closed position the valve must withstand the possible fluid pressure in the system, without leakage. Since a normally open valve must be active in this situation, one must analyse the open/closed ratio under operation in order to make a choice for a normally open or normally closed valve. It is also possible to design a valve with pressure compensation, such that the over pressure to be controlled is reduced [12] or even be used to enhance the valve position [10],... 

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