Pneumatic Knocker

1. Design and Operation Principles

The Pneumatic Knocker achieves a high grade of impact energy by the spontaneous release of the accumulated compressed air pressure. Figure 1 shows the design.
The piston (1) designes 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 loosens from the anchor plate, is very highly accelerated vy 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. When deaarating the cylinder, the piston will be pressed back into the starting position by means of the spring (5).

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, referred to as impact energy E = m · v²/2 and impulse J = m · v. There is no impact force or out-of- balance such as vibrators generate. The effectiveness of the knocker may be judged 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."

Material flow problems can be solved by the operating personnel either by actuating a switch or a valve or be totally prevented by an automatic control.

Fig. 2 may provide a rough reference for chosing the adequate size and number of Pneumatic Knockers for round silos of 60° cone. In case of rectangular containers, the knockers are installed at the longer sides. For product conveying out of a silo, cycle times of 5 to 20 seconds are recommended. Too frequent knocking should in any case be avoided, otherwise the product would be compressed. Continuous product flows such as in dust filters and spray towers, should be knocked in cycle times up to 30 seconds. If the layer of product becomes too thick, an avalanche-like break-off could block the outlet or overload the following machines. If there are several knockers mounted at the periphery of a container, they are to be actuated one after the other, in order to have a more constant product flow and compressed air consumption. When emptying container scales, one should knock 2 to 4 times in a cycle time of 1 to 4 seconds. We also supply the respective control units.

3. Sound Insulation

The Pneumatic Knocker has the greatest effect, when the impact is transmitted without damping to the silo wall. It is, therefore senseless to damp the impact in order to reduce the noise, for this would also reduce the effectiveness of the knocker. That is why the noise arising can only be reduced by sound insulation. We supply the necessary Sound Insulation Hoods (KSH) for the knockers, self-adhesive Sound Insulation Plates (KSP) for the container wall, and Sound Absorbers for the deaeration borings of the solenoid valves.

4. Safety against Explosion Accidents

The Pneumatic Knocker may be used in the ex-range, if the solenoid valve and the control system are explosion-proof and the knocker is scavenged by external air through the air-scavenging outlets.

5. Installation and Operating Instructions

5.1 It is only allowed to install and use the Pneumatic Knocker and the Impulse Knocker as a knocking and evacuating device on silos, containers, cylinders and walls, after having paid special attention to the instructions and in accordance with the technical data given therein. Installation, maintenance, pre-operational and operational as well as post-operational handling of the equipment and the accessories shall only be carried out by trained and qualified personal in compliance with the legal prescriptions and safety regulations. The knocker has to be installed, secured and controlled so that - in case of loosened screws, cracked welded joints or other damages whatsoever - there will be no danger for persons, animals, products or objects to be damaged or polluted. If the Impulse Knocker is applied, the space between piston rod and impact wall should be protected against grasping-in and the knocker be fixed in such a way that maintenance and exchange will be possible during operation without any danger.

5.2 The knocker shall be actuated only after having been tightly screwed on, otherwise its own bottom plate may be destroyed.

5.3 The area to be knocked should be able to swing so that the impact can expand in all directions. Reinforcements and ribs are to be avoided.

5.4 It should only be knocked when the silo outlet is open or the following conveying equipment is working, otherwise the product will be compressed.

5.5 The Welding Plate AP is to be welded directly onto the silo sheet at the lower third of the silo cone and adjusted by flattening the round part or by means of large welding seams. If it is fixed to smaller diameters, to insulated, rubberized or aluminum silos, please see our recommendations in leaflet 100-089.

5.6 The Pneumatic Knocker has to be screwed in such a way that the lateral deaeration borings are directed to the bottom. In case of larger dust quantities, the deaeration borings must be protected against dust by screwing in sound absorbers as filters or by wrapping the knocker with filter mats. Humid or aggressive vapors should by no means be allowed to enter through the deaeration borings.

5.7 According to Fig. 3, the Pneumatic Knocker is connected with Solenoid Valve MV, Maintenance Unit WE and Impulser TG. The compressed air is adjusted at 0.5 bar above the release pressure of the knocker (approx. 2.5 to 3.5 bar). The length of the operating time should be so adjusted to make sure that the impact will be released (approx. 0.5 to 2 seconds). The interval time is to be adjusted according to the operating conditions, but as long as possible and at least longer than the deaeration time of the knocker. For shorter interval times, a larger solenoid valve and, in addition, a Quick-Action Deaeration Valve SE should be provided for.

5.8 During operation, all screws must be checked as to their tightness and, if necessary, be tightened by means of a torque wrench. As to the maintenance unit, the condensate must be discharged from the filter, oil with 15 to 30 cSt be refilled, the adjusted pressure and the oiler function be checked again.

6. Pneumatic Impulse Knocker

The Pneumatic Impulse Knocker, a special design of the Pneumatic Knocker, is provided for rotating drums and moving parts to be knocked off, since the piston rod springs forward and backward at a high speed without remaining in the end position.

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