PONGO Started life as a simple experiment to test the validity of the SOG system that seems to be creeping onto many Thetford motorhome loos.
Having had the justification from a SOG sales person I shuddered at the price of over £80.00 and was also concerned that if the SOG system was not a success I would be left with a loo with a hole cut in the emptying spout in a very inconvenient position.
So, the challenge was to produce a system that cost very little and did not compromise the integrity of the loo. The first piece of luck was that I found a container that had the same screw thread and diameter as that of the emptying cap of the Thetford. Using some squashed copper pipe I made a right angled adaptor that was a push in snug fit into my newly drilled plastic cap. It was thin enough to fit in the remaining space between the end of the spout and the compartment sidewall. I fashioned from heat shrink tubing a shaped extension to my copper work that when in place would put the "vent" in the top corner of the loo aperture. This I thought should minimise problems associated with fast cornering! In the event it seems that fast cornering a motorhome does not cause the cassette contents to get into the copper pipe at all.
The second task was to fit a small sealed micro-switch that would operate when the trap was opened. The trap has a rotating mechanism and it was easy to have the micro-switch operated when the trap was closed and to release the switch when the trap was opened.
Task three was to fit a small brushless DC Papst fan motor to extract air from the loo compartment. Unlike the SOG which only extracts from the cassette I took a simpler approach of pulling air from the complete loo cavity. This was well sealed and seems to be OK.
Their already exists a fuse protected 12 volt supply within the loo compartment to power the flushing pump, this was connected into to run the small extractor fan via the micro-switch.
A test week end showed that PONGO performed as we hoped. Perfect operation on site over 4 days. No whiff's whatsoever. The One lesson learnt is that if you are travelling and stop to use the "facilities" in a hurry then it is prudent to let the contents of the cassette settle for a few minutes before opening the trap. Alternatively, open the trap with the lid down for a few moments to give PONGO a chance to extract the vapours from the stirred up .....
REVISIONS NOV 2005
OK, so perhaps PONGO can do with a little more power to enable instant use anywhere. The duct around the fan which together with pipe work turned out to be very effective but fiddly to remove when the cassette had to be removed (same problem as with SOG) so I took the pragmatic American approach, "If all else fails just fit a bigger engine". Hence a fan of four times the suck was fitted.
This fan of course requires a bigger air path hence a deeper outside cover.
And the copper and silver soldered tube work fitted in the spare cap was replaced with another that has a bigger internal cross sectional area throughout and does not require any shrink tubing to provide corners.
But in position it just nestles in position without compromise.
In essence, the system of applying negative pressure works simply if you have plenty of pressure to spare.
The smoking match held over the bowl test now works very well. Smoke does go downhill, quite fast!
Latest revisions to PONGO further down the page.
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