We would like to present a rather rare, but nonetheless – a very advantageous solution included in the WOLFF GROUP portfolio. The solution is a pressure chamber lock with the functionality of explosion decoupling. The solution of this type will be supplied for one the manufacturers of bathroom ceramic products as an alternative for the currently operated rotary feeder which is quickly becoming damaged due to erosion.
In some situations, pressure chamber locks make a great alternative to rotary feeders. They both fulfill the same function, i.e. they are used to evacuate bulk materials from different types of equipment and process devices and at the same time restrict airflow. Both types of machines can also provide the functionality of so-called explosion decoupling, i.e. restrict explosion propagation inside process systems.
In order to protect the process system against effects of the explosion, one should not focus only on individual devices. A process system is a closed system. An explosion in one of the elements, even if protected by suppression or venting, can spread to other elements in the system. This type of propagation is a result of residual flame breaking down through ducts, pipelines and transfer stations to adjacent devices. For this reason it is required to use decoupling systems, also called isolating systems. The chamber lock is an example of this type of systems.
Contrary to a widespread belief, rotary valves do not ensure complete tightness of the system. This is a direct result of their construction – there is always a clearance between the rotor and the body, this is required for the device to operate correctly. For this reason, in systems with pressure difference (dust extraction, central vacuum, pneumatic transport, etc.), the air with dust particles flows through the clearances, causing the body, rotor and rotor shaft to erode. The speed of this process depends largely on the pressure difference between the inlet and outlet of the rotary valve, the abrasion properties of the dust and the material used to construct the rotary valve. Based on experience, it seems that if the pressure difference exceeds 1.5 bar, the use of rotary valves should be seriously reconsidered. Of course, in these situations, abrasion-resistant materials can be used but this results in significantly increasing the prices of the equipment.
There is an alternative, free of the limitations described above – a pressure chamber lock, which guarantees full tightness of the system even in case of pressure differences of 16 bar. The device consists of two butterfly throttle valves installed on both ends of a vertical pipe (chamber). In order to isolate the pressure and effects of explosion, only one of the throttle valves can be open at a time.
When material is supplied to the chamber, the top butterfly valve is open (the bottom valve is closed). Then, the top valve closes and the bottom valve opens, resulting in the transfer of the material from the chamber to the system below the lock. The bottom valve closes and the entire cycle is repeated at set time intervals. Both valves are connected to a single controller in order to ensure that only one butterfly valve is open at a time.
Advantages of the system:
- 100% tightness when the valves are closed,
- low wear due to abrasion,
- low cost of wear parts.