1. Design and Mode of Operation
The Pneumatic Knocker achieves a very high impact energy due to the spontaneously released stored compressed air energy. Figure 1 shows the design of the knocker.
The piston (1) designed as a permanent magnet, adheres in the end-position to the anchor plate (2) until the compressed air fed through the lid (3) overcomes the magnetic force. The impact piston (1) loosens from the anchor plate (2), is very highly accelerated by the accumulated compressed air and hits onto the striker (4) with a speed of 6 to 7 m/sec., which transmits the impact to the silo wall. After deaeration of the knocker, the impact piston (1) is pressed back into the starting position by means of the spring (5).

Figure 1

2. Application
The Pneumatic Knocker is used for bulk goods with material flow problems as for instance bridge, siphon and residue formations, when high speed shakers and vibrators with soft sine-shaped oscillations are no longer effective. The effect of the knocker is comparable to that of the famous “silo hammer”, but without distorted silo spouts additionally impeding the material flow.
The Pneumatic Knocker produces an ideal elastic shock that is specified as the impact energy E = m/2 × v2 [kgm/s2 = Nm] and as impulse J = m × v [kgm/s = Ns]. There is no impact force or out-of-balance such as vibrators generated. The effectiveness of the knocker is evaluated according to the following rule:
If the product can be knocked off or be brought to flow by a hand hammer, the Pneumatic Knocker would also be effective. The knocker is normally controlled by an electrical control system with a solenoid valve.
The area to be knocked should be able to swing so that the impact can expand in all directions. Reinforcements of the silo walls and additional ribs should be avoided, as this increases the weight and the strength of the silo walls and thus reduces the effect of the knocker.