Underground Exhaust

The ground pot was usually supplied if the engine was near humans as it would be for a StartoMatic. They were not usually buried as it stops them moving which can lead to expansion/contraction problems on the exhaust system. The alternative was, and is, to build a brick chamber underground. Either option reduces the exhaust to near silence, and certainly quieter than the inlet. hth Roland

There are three basic methods of silencing internal combustion engines.

1. By discharging the gases into an enclosed non-resonating chamber of large capacity where they will be expanded and where the waves will expend themselves before the gases pass through the chimney to atmosphere.

1. By passing the gases on the way from the engine to atmosphere through a silencer, fitted either with baffle plates to break up the gases or absorption chambers which allow the waves to expend themselves in a sound-absorbent material.

2. By dissipating the energy of the gases in a " snubber," which consists of a silencer having two parallel paths for the exhaust gases, a high velocity path for the slug and a low-velocity path for the following exhaust gases expelled from the cylinder during the exhaust stroke or scavenging period.

Obviously, the wavelength of the sound pulse is critical and with engines rigged for display, a long pipe will frequently be all that's required to do away with the sharp crack of combustion. It has to be the right diameter/length, though, the Reid at Astle Park had a nice long pipe - and a crack like a field gun!

A solid cast iron pot will absorb sound waves of itself and one often sees them mounted on the trolley with a big engine that in real life would have been firmly bolted to a concrete plinth! A brick built chamber underground is even better as long as everything is very rigidly mounted. Even so, I can see that the latter would be prone to leakage despite the best of efforts.

Could be good fun if the beast was hard to start and the chamber filled with combustible mixture .........

regards,

Kim Siddorn.

Could be good fun if the beast was hard to start and the chamber filled with

a pumping station near me has mufflers buried underground. the noise from the engines is acceptable driving by but i understand there's a shock wave through the earth that can be felt/heard in nearby houses. we stopped to look at the engines, they had flywheels six to seven feet in diameter. single cylinder, etc. it's been years since we saw them. no more info on the mufflers. sammmm

(Snipped)

I have often seen buried mufflers, esp. farm lighting sets. Usually consisting of a 44-gallon drum buried outside the engine shed. Very effective they are too, until/unless they blow up - in one case an Armstrong Siddlely Start-o-matic cranked over for quite a few revs before firing, then Whooomp! Showers of dirt & dust, loud ringing in the ears, the tinkling of pebbles descending upon the shed roof and a muffler no longer buried ... Accumulated gas. Not only petrol engines - diesel is just as dangerous.

Ah, we made our own fun in those days!

JW­²