Bleeder and venting valves remove and admit gases or air mechanically from/to tanks, pipelines and vessels. They are float-controlled valves which closes are the liquid increases and open as level falls.
An increasing liquid level lifts the float and shut down the control devices, in most cases through a structure of levers. If the liquid point downs because air is entering the system or the plant is being started up, the valve will open and either admit air or release the air from the system.
Start-up bleeder and venting valves
Are used to vent low-force plant system when such systems are filed or started up. The float works directly on the cone. They have a big seat diameter to make sure quick venting for forces under 0.1 bar. During work these control devices are kept closed by the inside system force. A quickly happening vacuum leads them to equalise and unlock the force. This stops damage which a vacuum may cause.
Continuous vent valves
Are used to get rid of air which build up as the plant works. They include a lever system which permits them to work at extremely high and low forces.
A non-return control device can be fixed to the exterior side of these control devices to stop air incoming the system. In this example they are real vent control devices, no air enters the system.
Double function bleeder and venting valve
Are combined start-up and continuous bleeder/ venting valves. They have a big seat for start-up operation and a little seat for continuous operation, which are managed by a float through a system of levers.
Both valve seats are unlock while the system is being filled. During system work the big seat is kept closed by the internal force. Any accumulating little air volumes are vented from the system through the little valve seat. If the force drops under 0.1 bar the big valve seat can unlock again. If a vacuum happens which may be caused, for example, by a pump failure, the big seat opens instantaneously and stops damage.
If subsequently a force surge runs back via the pipeline, the big closes causing the air volume which has entered the system to work as a damper while escaping to environment through the little seat.
Operating pressure range
You should pick an operating force range which covers the highest force that may happen, as or else the vent control device will not unlock. You should pick the size and type of vent valve according to the air volume to be removed at operating force. You will find the right tables in the data sheets. The throughout capacities given in these tables apply to a completely open valve i.e. When the system is starting or as long as the liquid point remains under the vent valve inlet. For continuous and steady venting e.g. of filter vessels, the throughput capacity should be decreased by about 30 percent.
To make sure perfect long life and work, continuous vent control devices should not be overdimensioned. If the throughput capability is excessive for a given so-called diameter, a superior operating force coupled with a also lower throughout may give the solution ,refer to this page know more about bleeder valve.