12322 Automatic reservoir drain valve

Discharged air from the compressor entering the reservoir goes through a cycle of compression and expansion as it is exhausted during brake on/off applications. The consequence of the changing air density is the moisture, which is always present in the air, condenses against the cold walls of the reservoir, trickles down to the base of the chamber and thereby forms a common water pool. Permitting water to accumulate may result in the corroding of certain brake components and in cold weather this water may freeze thereby preventing the various braking valves from functioning correctly.

The object of the automatic reservoir drain valve is to constantly expel all the condensed unwanted water into the atmosphere from any container it is attached to.

Operation (Fig. 12.27(a-d)) If there is no air pressure in the braking system, both the inlet and exhaust valves will be in the closed position (Fig. 12.27(a)). Initially, as the compressor commences

ic) Diaphragm in halance

Fig. 12.27(a-d) Automatic reservoir drain valve ic) Diaphragm in halance

Fig. 12.27(a-d) Automatic reservoir drain valve to charge the reservoir, the air pressure rises and pushes open the inlet diaphragm valve. Condensed water collected above the diaphragm will now gravitate to the lower conical sump of the valve during the time the pressure is rising (Fig. 12.27(b)).

When peak governor pressure (cut-out pressure) is reached, the compressor is unloaded, cutting off further reservoir air supply so that the pressure above and below the valve diaphragm equalize. As a result, the diaphragm support below the diaphragm closes the inlet valve (Fig. 12.27(c)). Air is consumed due to the application of the brakes. There will be a reduction in reservoir air pressure so that the trapped air pressure below the diaphragm will be slightly higher than that above.

Consequently the pressure difference between the two sides of the diaphragm will be sufficient to lift the middle portion of the diaphragm and the conical exhaust valve clear of its seat (Fig. 12.27(d)). Thus the air trapped underneath the diaphragm forcibly expels any condensate or foreign matter which has collected into the atmosphere.

Manual draining of the reservoir with the automatic valve is obtained by pushing up the vertical pin situated in the base of the exhaust port.

This type of automatic drain valve is designed for large reservoirs positioned away from the compressor. It is unsuitable for small sensing tanks or small volume condensers mounted near to the compressor.

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