Leakage compensation

Fig. 4.1-35. Diaphragm compressor (HOFER). a, Diaphragm b, Gas space c, Discharge valve d, Suction valve e, Diaphragm cover f, Perforated plate g, Hydraulic cylinder h, Oil overflow valve i, Oil return j, Cylinder cooling k, Check valve 1, Crank drive m, Cooling-water in/out n, Oil-cooling coil o, Oil chamber p, Oil injection (leakage compensation) q, Compensation pump r, Check valve s, Oil supply.

The methods described here are illustrated in Figs 6.11 and 6.12 for the continuous flow technique, and in Fig. 6.13 for leakage compensation. 

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

Protective gas air (from a compressed air grid) Mode of protection leakage compensation. 

The protective gas is air, supplied from the compressed air grid in the coal mine. Operational mode is leakage compensation. 

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. 

After maintenance or repair, the door will be closed and subsequently locked, and inlet and outlet valves are opened to start the purging procedure and subsequent normal operation. The mode of operation is leakage compensation, i.e. the protective gas outlet pipe and the common purge flow or volume measuring device are active during purging only. 

Generator-Type of protection EEx p II T2 Protective gas air Operational mode leakage compensation Rated power 1050 kVA, 840 kW Rated voltage 400 V 3 AC Rated frequency 50 cps Rated speed 1000 min-1 Cooling air/water heat exchanger... 

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 )... 

Table 7.2 indicates that a release of combustible substances out of the containment system can be handled in a safe way, even in the case of an undefined flow of protective gas using leakage compensation and continuous flow of protective gas as protective techniques. 

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... 

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