Tornado Grenade – How it Works
For some time I wrestled with the idea of publishing this “How it Works” article. On one hand I didn’t want to hand over a couple years of R&D to some clone shop. On the other, I do want to help my end users come to a practical appreciation of how their Tornado grenade works. In the end I realize that an elegant product usually ends up being simple enough to reverse engineer so I might as well provide a well photographed and clear explanation of how my product works before too much misinformation crops up. My patent will be enforceable soon and I have to admit that manufacturing these things is a bit of a bugger for me and I designed the damn thing so maybe that’ll keep out the copy-shops.
This article is the first of a few practical articles I plan to publish on my Tornado grenade. It will set the stage for a troubleshooting guide that I am working on as well as a maintenance video.
Please familiarize yourself with this annotated section photograph. All of the parts in the Tornado will be referred to by the names indicated here.
Zones of the Tornado Grenade:
- Delay chamber
- BB spirals
Parts of the Tornado Grenade
Bumper: Rubber bumper with integral plug and plug lanyard
Top Cap: Machined aluminum cap which provides timing delay functions
Delay Restrictor: Partially blocked opening in the TC which acts as a timebase for the grenade delay
Shuttle: Grenade SuperPart! The most complicated part which participates in timing, gas storage, gas filling, and firing processes
Fill Valve: Brass valve screwed into the core of the shuttle
Upper Delay Seal: Rubber seal sealing between the reservoir and the delay chamber
Lower Fire Seal: Rubber seal sealing between the reservoir and the manifold
Stem Orings: Orings on the stem of the shuttle
Body Tube: Machined aluminum tube which holds all the pneumatics together
Phases of Operation
The Tornado has several phases of operation. This section will describe these phases in sequence starting from a loaded state with the pull pin inserted into the 3s delay hole in the TopCap through timing stages, ending with firing stage. The last part of this section will describe how the timing pneumatics are reset before refilling with gas.
Initial State: Loaded and pinned
In this state the shuttle stem is firmly pressed against the pull pin. The shuttle has two flanges of different diameter. The upper delay seal has a larger seating diameter than the lower fire seal. This gives the UDS a larger cross sectional area than the LFS. Pressure contained in the reservoir applies equally to all of the surfaces inside the reservoir (i.e. 120psi acting in all directions), but the larger area of the UDS results in a higher force acting on that seal than the force acting on the LFS.
The force applied by pressure on a surface is described by the pressure, acting in units of force per unit area, multiplied by the area it’s applied to. In the case of the shuttle, the forces acting on the UDS and LFS are in opposite directions (pulling the shuttle flanges apart from each other) but the UDS force is higher which results in a net force which pushes the shuttle upwards against the pin.
Intermediate State: Pin pulled and shuttle moving
The net force pushing the shuttle upwards gets the shuttle to move which compresses a volume of air in the delay chamber. This volume is trapped between the UDS pushing upwards and the orings on the shuttle stem. Initially, the shuttle moves fairly quickly until the delay chamber air is compressed until the pressure on the upper side of the UDS counters the net force acting on the shuttle. The trapped air in the delay chamber is allowed to leak slowly out of the delay restrictor which acts as a time base for the grenades timing delay. Pressurized air leaks out of the delay chamber via the DR.
End of delay State (delay blowout)
Shuttle oring stem clears small bore in Top Cap When the lower oring on the shuttle stem clears the shoulder between the small and large diameters in the stepped bore in the top cap, a secondary outlet is provided for the air trapped in the delay chamber. Previously the only outlet for air in the delay chamber was through the DR. When the lower oring clears the shoulder into the larger bore, a comparatively large gap opens which allows the remaining delay chamber air to escape rapidly. This removes the pressure balancing the net force on the shuttle and allows the shuttle to rapidly snap upwards until it bears against the top cap.
In summary, when the shuttle moves far enough, the stem orings act as an opening valve which allows the delay chamber air to rapidly escape at a particular position thereby allowing the shuttle to rapidly move. There are two stem orings, but their functions are essentialy similar. They provide sealing between the stem and the small bore in the topcap. Two are used to provide as seal over most of the travel of the shuttle stem.
Setting the delay pin to a shorter delay setting reduces the amount of air initially in the delay chamber which reduces the amount of time before the shuttle reaches the delay blowout position.
Firing State (reservoir blowout)
Air completely vented from delay chamber When the shuttle rapidly snaps upwards, the LFS is pulled into the larger bore of the body tube. This opens up a gap around the LFS and allows gas to dump into the manifold and pressurize the bb spirals and things get exciting fast. Proxy spherical schrapnel rockets out of the spiral passages which causes the grenade to breakdance and fun is had by all.
Expanding gas pushes into the side holes in the body tube. If the valve cover is removed, there’s an even bigger opening which vents gas outside of the grenade instead of pressurizing the bb spirals. If the grenade is overpressurized, and the relief valve in the shuttle doesn’t pop, the rubber bung in the valve cover is pushed inside out and it pops out of the valve cover providing a failsafe pressure release.
Delay plug is pulled out of topcap and valve tool bears against shuttle stem Before resetting the delay plug is pulled out to provide an unrestricted opening to allow air to flow into the delay chamber when the shuttle is being reset. Don’t forget to put this plug back in or you’ll leave this large unrestricted opening which will immediately put the grenade into delay blowout when you pull the pin.
Whew! Thanks for reading this far. I’m working on the next article in this series: troubleshooting your grenade. The first step is to understand how things work before diving into tearing things apart. Unfortunately producing this content is a lengthy process, but I’m working hard to bring it to publication.