Water tends to build up in compressed air systems. You need to fit a drain valve at the bottom of your air receiver, on your filters and separators and at any point where water would tend to collect .
There are four types of drain valve and there are pros can cons for each.
Manual Drain Valve
 Manual Drain Valve |
You can use a hand operated valve – ball valve, needle or gate valve or other type of valve. Simply go round regularly and open the valve to let the water out, closing it again when air comes out instead of water.Pros – The most inexpensive way in terms of components to drain water from your compressed air system
Cons – Probably costs more than you think in terms of the time it takes each day or week. Will you remember? What happens during holidays or sickness? There is also a large potential cost if you forget. |
Mechanical Drain Valve
 Mechanical Drain Valve |
This type of drain valve has a float. When the water rises above a certain level the drain opens and lets the water out.Pros – Cost. Prices range from inexpensive to very expensive. Good option areas in which electrical items are restricted or prohibited due to an explosion risk. Also a solution if there is no electric supply near by. Does not waste any compressed air.
Cons – Maintenance issues. If there is dirt or contamination in the air supply it can interfere with the float mechanism and cause the drain not to open or to get stuck open. |
Timed Drain Valve
 Timed Drain Valve |
This type has a solenoid valve and a timer combined into one. The opening time and the interval time can both be set. For example it can be set to open for 2 seconds every 45 minutes. When buying a timed drain valve it is important to check the orifice size – a larger orifice will be more reliable as it is less likely to get blocked by contamination. Valves with larger orifice tend to cost more.They often have a strainer fitted immediately upstream. It is better if you can managed without a strainer as this becomes a maintenance item by itself. Rather fit a valve with a larger orifice and no strainer.
Pros – Very simple and normally reliable. Can be inexpensive compared to other types of automatic drain and avoids issues with air locks if the drain point is very near the ground. Cons – Wastes compressed air. As you need to set the times for the worst conditions, the drain time will be generally longer than it needs to be so some compressed air will be exhausted as well as water. Over a 12 month period the cost of this lost air can be considerable. There are also maintenance issues with stainers and contamination and there is no easy way to monitor the operation of the drain or feedback data to building management systems. |
Electronic Level Actuated Drain Valve
 Electronic Level Drain Valve |
At the heart of this item is a capacitive sensor with two set points. When the liquid level reaches the top point a valve opens and lets the liquid drain out until it reaches the bottom point when the valve closes again.This type of valve often contains electronics which can send a signal to a building management system to report that a fault has occurred.
Pros – It does not waste any compressed air and is normally good at handling contaminated condensate. It also has the possibility to be connected to a building management system. Probably the most cost effective way to drain condensate overall in the long run Cons – Initial Cost. |