Automatic drain valves remove mixtures of water and compressor lubricants from compressed air systems. An automatic drain valve eliminates the need for a maintenance worker to patrol the plant, manually dumping liquid from the air system. An Automatic drain is a 2/2 valve that closes when the system is pressurized. The Drain opens when liquid accumulates and causes the float to rise, and on depressurization.
Draining contaminants from your compressed air or distribution systems is mostly a simple process, however, some applications can call for more sophisticated draining mechanisms. This tutorial describes several different draining mechanisms and identifies the solution each mechanism provides to specific application parameters, such a low flow, difficult access, or differential pressure.
Semi-automatic Drain:
Semi-automatic drains operate when the airline is depressurized. A semi-automatic drain is basically a NO 2/2 valve that is held closed by pressure acting on it. It is semi-automatic because when the filter is pressurized, the drain can still operate manually by pushing the tube in the filter, which then protrudes outside the filter bowl.
Automatic Drain:
An Automatic drain is a 2/2 valve that closes when the system is pressurized. The Drain opens when liquid accumulates and causes the float to rise, and on depressurization.
Automatic Drains are good for when the filter located in the application makes access for servicing difficult, or for when equipment is in continual use and disruption for draining is not a preferred option. Applications where large quantities of water can accumulate over a short period of time justify the installation of an Auto-drain.
Low-flow Drain:
A low-flow drain can be used when the compressor capacity in the application is insufficient to close a number of standard automatic drains. Low flow drains are less effective at clearing contaminants, and therefore should only be used when a standard automatic or semi-automatic drain cannot be used due to application.
‘Spitter’ Drain:
A Spitter drain is used when there is differential pressure above the drain’s diaphragm and below it. The drain momentarily lifts and ‘spits out’ the condensate collected under the drain. A ‘Spitter’ drain is suited to applications where there are rapid increases in inflow, resulting in differential pressure.
Constant Bleed Drain:
Using a Constant Bleed drain means having a small hole in the bottom of the bowl, allowing condensate to be constantly removed. A Constant Bleed drain should only be used when the flow is too low to use auto-drain and when manual draining is not possible.
Drip-leg Drain:
A Drip-leg Drain is for protecting distribution systems from malfunction or damage. When systems having varying flows or shut down at the end of the day, a Drip-leg Drain can be used to remove water that has collected in the low points of distribution pipework. A Drip-leg Drain is achieved by running a vertical pipe down from the low points into a Drip-leg drain where an automatic drain will expel the water.
